<![CDATA[Radio Boat Anchor

<![CDATA[Radio Boat Anchor - Blog]]>Thu, 07 May 2026 06:31:38 -0700Weebly<![CDATA[AIWA AV-D25U Stereo AV Receiver, when a repair isn't a repair at all]]>Wed, 17 Mar 2021 17:13:28 GMThttp://www.radioboatanchorblog.com/blog/aiwa-av-d25u-stereo-av-receiver-when-a-repair-isnt-a-repair-at-all

I spend a lot of time searching for consumer electronic equipment, that is need of repair, on online auction websites. The more of a "basket case" a piece of electronic equipment is, the more I want it as I enjoy a good repair/restore challenge.

I came across this AIWA Model AV-D25U Stereo AV Receiver, on a charity auction site, and was intrigued. Its listing indicated that it powered on but did not emanate any sound.

I was the only bidder on it and paid $9.99 plus shipping.

The charity auction site did an excellent job of packing this Stereo AV Receiver, for shipment. It was encased in a bubble wrap cocoon that and took me several minutes to unwrap, after removing it from its shipping box.

The AIWA Model AV-D25U has analog audio inputs for Tape, Phono, Auxiliary, CD and Video. Looks like it can also be used to switch audio/video input to an external TV monitor.

There are connections for an AM loop and an FM long wire antenna, required for the radio reception.

This stereo receiver features multiple speaker outputs, including one for an external subwoofer. In addition, there are speaker outputs for Surround Sound, Center, and A and B speakers sets.

I bench test all electronic items I purchase from auction sites, just to verify operation. I connected speakers to A Speaker output, connected an external FM antenna, then plugged it into AC power. I then proceeded to powered it on, switched to FM stereo, and adjusted the volume to mid range. I heard......"nothing", like the auction listing described.

Then, I noticed on the lower left front of the AIWA Model AV-D25U two switches, labeled "Front Speakers", both were set to off. I turned on the one labeled "A" and "presto" I suddenly heard sound from the speakers!

After throughly testing, I determined that there was absolutely NOTHING wrong with this stereo receiver. It would have worked fine with the proper switches configured!

Most likely, a worker at the charity auction site had a finite amount of time to test each piece of consumer electronic equipment. He/she connected the speakers to the A speaker output and didn't realize this speaker output was disabled on the front panel.

Detailing

Even though the AIWA Model AV-D25U worked perfectly, it was quite dirty, so I decided to detail it, inside and out.

First, I removed all the accumulated dust from the inside of this stereo receiver, using compressed air.

After cleaning, I applied a coat of car wax to the outside of the metal enclosure, then buffed with a lint free chamois.

I applied a coat of protectant, similar to Armor All, to the plastic facade of the AIWA Model AV-D25U.

I cleaned the back of this stereo receiver with Windex and a lint free chamois. I used a Q-Tip, moistened with Windex, to get into difficult to reach areas, like at the base of the RCA Jacks.

Here is a picture of the clean AIWA Model AV-D25U chassis, prior to installing the metal enclosure.

I tested the AIWA Model AV-D25U, one more time, after it was all assembled.

Finally, my newly acquired AIWA AV-D25U Stereo AV Receiver took its place in my stereo rack. With my other refurbished stereo equipment.

Conclusion

It is important to first test electronic equipment, acquired from online auction sites, even if it is listed as "for parts or repair". You may also find a "gem" of electronic equipment, that does not require any repair at all.

]]><![CDATA[My Homebrew SuperHet Receiver Build]]>Thu, 18 Feb 2021 02:06:22 GMThttp://www.radioboatanchorblog.com/blog/my-homebrew-superhet-receiver-build

I have built many Regenerative radios and decided to give building a SuperHet radio a try. My SuperHet radio uses hand wound coils in the Antenna transformer, two IF transformers, the Local Oscillator, and the Beat Frequency Oscillator. It covers the 80M or 3.5Mhz band. The Antenna transformer and Local Oscillator coil used in the Frequency Converter or Mixer Stage are pluggable, allowing them to be swapped out to cover other bands. In the future, I hope to create a pluggable Antenna transformer and Local Oscillator coil for the standard AM broadcast band. The blue radio in front has the same number of IF stages as my homebrew SuperHet. I set it there to give you an idea of scale.

SuperHeterodyne Radio Theory

Invented by engineer Edwin Armstrong, a superheterodyne receiver, often shortened to superhet, is a type of radio receiver that uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carrier frequency. Virtually all modern analog radio receivers use the superheterodyne principle.

My Inspiration

I had some trouble finding plans for a vacuum tube superheterodyne receiver on the Internet. I put the question to an antique radio forum, I often frequent. Another forum member suggested I acquire a copy of the now out of print "The Impoverished Radio Experimenter Volume 5", a small booklet that completely covered the topic of a homebrew vacuum tube superheterodyne receiver. This book was my inspiration as it covered the build of such a receiver and included a whole alignment and troubleshooting section.

The Impoverished Radio Experimenter Volume 5 on Amazon:

Circuit Theory

Above is the schematic of the homebrew SuperHet AM (amplitude modulated) receiver I am to build. As you can see, it consists of a Frequency Converter or "Mixer" Stage, an IF (Intermediate Frequency) Amplifier Stage, and a Detector Stage. This radio only has one IF amplifier stage where most modern radios have two. Adding another IF amplifier stage would increase the size of an already rather bulky radio. Tuning is accomplished by adjusting the frequency of the LO or Local Oscillator, the result is always a 400kHz amplitude modulated signal, feeding the single IF Amplifier Stage. The IF transformer before and after the 6SK7 tube "pass" the 400kHz signal, while acting as a direct path to ground for all other frequencies. One triode of the 6C8 acts as the Detector which strips the RF (Radio Frequency) carrier, leaving the AF (Audio Frequency). The second triode acts as a BFO or Beat Frequency Oscillator that, when enabled, allows the detection of CW or Carrier Wave transmissions.

Layout

The base of my SuperHet receiver is a 12" x 20" small wooden "craft" pallet, I obtained from our local craft store. During one of my trips with my wife to the craft store, I noticed that they had a complete selection of small wooden boxes and pallets that are ideal for homebrew receiver construction. I first drew a 1:1 scale layout of the placement of all components on the craft pallet, then I drew the wiring between the components. It's important to get the layout nailed down, prior to construction.

Shielding

The IF transformers and BFO helical coils need to be contained in non-ferrous shielding, so as to prevent crosstalk between one another, and to avoid interference to any nearby electronics. I chose to build the shielding enclosures of cardboard clad in aluminum foil. I carefully cut pieces from an old Chewy (online pet supplier) cardboard shipping box, using an X-Acto knife, and a framing square as a straight edge to cut along.

A 2" x 2" "window" needs to be cut in the cardboard divider, or septum, that separates the two IF coils, within the shielded enclosure. The "window" needs be centered and at the same height as helical coils, allowing for maximum coupling between them.

I proceeded to cut the remaining cardboard pieces, needed for the shielding.

Each shield enclosure was taped together using masking tape, to prepare for gluing.

Elmer's glue was applied to each seam of the shield enclosure. I then used my index finger to remove the excess glue, forming a nice bead.

Each shield enclosure requires "feet" so that it can be mounted to the wooden base. I used a couple blocks of wood to keep them in place, during the gluing progress.

Each cardboard shield enclosure must be clad in a non-ferrous metal, in this case aluminum foil. I used an X-Acto knife to cut the required aluminum foil panels, to be affixed to the shield enclosures.

Elmer's glue was then applied to the sides of the cardboard shield enclosure.

The aluminum foil panels were then affixed to the cardboard shield enclosure.

Here is the finished BFO coil enclosure.

I then tested to ensure that there was continuity between aluminum foil panels.

Aluminum foil straps are required to make contact with the foil panel, affixed to the wooden base.

I built two more cardboard shield enclosures, one for each IF transformer.

The divider, or septum, that separates the two IF coils within the shielded enclosure, needs to be clad in aluminum foil as well. The foil over the 2"x 2" window needs to be cut.

Then folded back and glued on the back side.

The divider needs to be centered then glued in place. The 2" x 2" windows needs to be toward the top of the cardboard shield enclosure.

Aluminum foil straps attached to the divider are required to make contact with the aluminum foil panel, affixed to the wooden base.

I then used Windex window cleaner, and an automotive chamois to remove glue residue from the foil clad cardboard shield enclosures.

Coil Winding

I built a Home Brew Helical Coil Winder Jig, to assist with this project.

It even has a magnetically triggered counter, that counts the number of coil turns.

Click on the link below, to find out more about my coil winder:
Home Brew Helical Coil Winder Jig

Winding the coil is as simple as turning the crank, while guiding the wire on the cardboard tube.

Once finished winding the coil, I placed a piece of masking tape to hold the varnished coil in place. I then applied a thin bead of E6000 clear adhesive, to hold the coil windings in place.

I scrapped the varnish from the end of the wires. I then used my Mega 328 Component Tester, to measure the Inductance and Resistance of each coil, in order to check for consistency between them.

Based on my calculations, each IF coil requires 260 turns of #30 magnet wire on a 1 5/8 diameter cardboard tube. The BFO coil requires 260 turns of #30 magnet wire, with a tap at the 195th turn. Each coil starts 3/4 down from the top of the cardboard tube. Four IF coils and one BFO coil were needed.

An Antenna coil is also required. I wound 13.5 turns of #22 magnet wire on a 1 1/4 inch four pin tube socket. At this point a loop for a tap is created followed by another 13.5 turns. The magnet wire is held in place with E6000 clear adhesive. After the ends of the magnet wire were scrapped clean of varnish, they were threaded thru the hollow pins.

A layer of masking tape was applied, then another seven turns of #30 wire was wound on the Antenna coil form, once again held in place with E6000 clear adhesive.

The ground connections of the primary and secondary winding of the Antenna coil are soldered to the same pin. The antenna input lead, secondary center tap, and secondary connection all get soldered to their own individual pins.

There should be continuity between each pin of the Antenna coil.

In addition, a Local Oscillator coil is needed for the Frequency Converter Stage. This is also #22 magnet wire on a 1 1/4 inch four pin tube socket. The Local Oscillator coil requires multiple taps. I wound two turns, starting at the bottom of the tube socket, and put a loop in for a tap. Then another two turns and another loop for a tap. Again, another two turns and another loop for a tap. At this point seven and a half turns then a loop for a tap. Finally, eleven and a half turns were wound.

The wires at the start and end of the Local Oscillator coil winding were soldered to individual tube socket pins. The third socket pin was soldered to a wire that goes to the tap at turn number four. The fourth socket pin was soldered to a wire that goes to the tap at seven and a half turns, past the tap at turn six.

There should be continuity between each pin of the Local Oscillator coil.

Wiring

Unfortunately, due to an issue with my camera, I lost many pictures of the construction of my SuperHet receiver. So the Saga continues with the wiring of my SuperHet.

Prior to wiring, I dry fit all of the components to the wooden base. I then removed the components and gave the wooden base a two-tone white and grey paint job. I then remounted the components, once the aluminum foil panels were glued to the areas where the cardboard shield enclosures were to be mounted. The white end caps on the aluminum panels hold the coils in place inside the cardboard shield enclosures. In order to neaten the wiring, I ran the tube filament wiring on underside of the wooden base, then drilled holes by each tube socket to run it to each tube socket. The other side of the tube filament wiring is terminated with Fahnestock clips.

I found it easiest to mount the tube sockets, used for connections to the Antenna transformer and BFO coils, upside down when soldering the wires to the terminals.

All resistors and capacitors were tested with my Mega328 Component Tester, before being soldered in place.

After the tube filament wires were connected to each tube socket from the underside, I ran the black wires used for the ground connections on the top of the wooden base. All the ground connections terminate at a central Fahnestock clip, located on the side of the base, where the filament connections terminate. I also wired each component connected to ground to the appropriate connections on the tube sockets.

Next, I ran the red wires for the 90 Volt B+ Voltage and the green and yellow wires used for coupling between the Frequency Converter, IF Amplifier, and Detector Stages. All 90 Volt B+ Voltages terminate at a central Fahnestock clip, located on the side of the base, where the filament connections terminate.

Wiring was then ran for the two front control panels. It is a lot easier to run the wiring, prior to installing them.

Time to wire the BFO/IF Gain control panel.

As you can see, the back of the control panel is lined with aluminum foil that is connected to ground.

Time to wire the Antenna/Tuner control panel.

The back of this control panel is also lined with aluminum foil that is connected to ground.

Small 6-70pf trimmer capacitors were soldered across the terminal strips that connect to the IF transformers and BFO coils. These will be used to adjust the resonant frequency.

Labels were applied next to the Fahnestock clips, close to the BFO/IF Gain control panel, to indicate the required input voltages, needed to power my SuperHet.

Labels were also applied next to the Fahnestock clips, close the Antenna/Tuner control panel, to indicate the Antenna and Ground connections.

Variable capacitors on the Antenna/Tuner control panel were labeled, as to their function. In addition, a label was added to the top of this control panel, to indicate the purpose of this contraption. I painted a silver line on each dial, to indicate its position.

The above picture was taken while testing my SuperHet, hence the alligator clips. Labels were added to the BFO/IF Gain control panel as well, below the IF Gain potentiometer, BFO Pitch variable capacitor, and BFO on/off switch. Once again, a silver line was painted on the BFO Pitch dial to indicate its position. The Fahnestock clips, that connect to the high impedance head phones, were also labeled.

Coil Installation

Time to mount the four IF and one BFO coils. The four IF coils are the same, while the BFO coil has a center tap. The coils cylindrical forms are pushed down on the circled white plastic caps, that are affixed to the wooden base.

Each IF coil lead was threaded through a white PVC insulator. Then the ends of each IF coil leads were scraped clean of varnish and soldered to the terminal strip. Finally, the white PVC insulators were secured to the wooden base, with E6000 clear adhesive.

A resistance check was done at each terminal strip, after the IF coil was soldered to it. It should read between 10 to 15 ohms, if the IF coil has a good connection.

The BFO coil leads were also threaded through a white PVC insulator. Then the ends of each the coil leads were scraped clean of varnish and soldered to the terminal strip. The white PVC insulators where secured to the wooden base with E6000 clear adhesive. Resistance checks were also done at the terminal trip, to ensure the BFO coil has a good connection.

Here is a picture of the IF and BFO coils wired in place. In addition, I plugged in the Antenna and Local Oscillator coils.

Cardboard Shield Enclosure Installation

Next, the cardboard shield enclosures were installed. Each one is fastened to the wooden base with four wood screws.

A washer was placed under the head of each wood screw, to prevent it from pulling through the base of each cardboard shield enclosure.

I had to shim each cardboard shield enclosure with washers, in order to ensure that it makes contact with the aluminum foil on the wooden base.

Each cardboard shield enclosure was checked for continuity with the aluminum foil, on the wooden base.

Testing and Alignment

The book "The Impoverished Radio Experimenter Volume 5" includes a handy schematic that shows all the proper voltages for each stage. At this point, none of the tubes were installed.

I used a Heathkit Model HP-23A Power Supply, to power my homebrew SuperHet.

I created a custom wiring harness to power my homebrew SuperHet. The HP-23A Power Supply has 6.3 VAC, to power the filaments. I used the -130 Volt DC output for the 90 Volt input voltage, just in reverse polarity. With load, the -130 Volt DC Output was close to -100 Volts DC. A jumper was also required between two points on the HP-23A's output socket, for it to power on.

I also connected a homebrew audio amplifier, with high input impedance, to the "Phones" connection on the BFO/IF Gain control panel.

After one last check of the wiring, I installed the 6C8 tube in the Detector Stage.

In order to test the Detector Stage, I removed the grid cap connection from the 6C8 tube, applied power and turned on the external amplifier. Next, I shut off the BFO switch. You know this stage is working if you touch the metal top of this tube and hear AC hum from the speaker. Don't worry, there is no voltage on the metal top of this tube. If no sound, perform voltage measurements at the tube socket, and compare with the Approximate Voltages schematic. Troubleshoot, if voltage measurements differ from the Approximate Voltages schematic.

I then Installed the 6SK7 in its socket, applied power, and perform voltage measurements at the socket of this tube. I then compared these voltage measurements with the Approximate Voltages schematic. At this point I would troubleshoot, if voltage measurements differ from Approximate Voltages schematic.

Alignment

I used my old Eico Model 324 Signal Generator for the alignment process.

For my homebrew SuperHet, alignment is the process of:
- Tuning all IF(Intermediate Frequency) transformers to the same frequency, in this case 400kHz.
- Adjusting the BFO(Beat Frequency Oscillator) Trimmer capacitor, so that it "Zero Beats" with the BFO capacitor's plates half meshed.
- Adjusting the LO(Local Oscillator) for the correct frequency range, in this case 3.5MHz to 4.0MHz.
- Adjusting the Antenna Trimmer capacitor, connected to the Antenna transformer, for maximum volume, with the Antenna Peek capacitor's plates half meshed.

The dial on my Eico Model 324 Signal Generator is not too accurate, I used my YAESU FRG-7700 to validate the frequency output of the Model 324.

IF(Intermediate Frequency) Transformer Alignment

I set my Eico Model 324 Signal Generator to a 400kHz internally modulated AM signal, then set the signal generator output lead near pin 4 of the 6SK7 tube. Once my homebrew Superhet and high impedance amplifier was powered on, I heard the faint sound of the signal generator. At this point, using an alignment tool, I adjusted the trimmer capacitor on the output side of the second IF transformer for maximum volume. I circled the trimmer capacitor I adjusted in the above picture.

Next, the trimmer capacitor on the input side of the second IF Transformer was adjusted for maximum volume. The yellow lead on the left side of the tube is connected to the signal generator.

Finally, the trimmer capacitor connected to the grid of the 6SK7 tube was adjusted for maximum volume. I then proceeded to "tweak" all three trimmer capacitors again for maximum volume.

BFO (Beat Frequency Oscillator) Alignment

This step is performed with power applied to my homebrew SuperHet and an high input impedance audio amplifier powered on and connected to the "Phones" connections on the BFO/IF Gain control panel. In addition, I set my Eico Model 324 Signal Generator to a 400kHz carrier signal only with no Amplitude Modulation, then set the signal generator output lead near pin 4 of the 6SK7 tube. I move the BFO Switch to the on position and set the BFO Pitch capacitor so that its plates were half meshed. I then adjusted the BFO trimmer capacitor for "Zero Beat". When adjusting the BFO trimmer, you should hear the audio pitch from the SuperHet get lower and lower, disappear then get higher again. The point at which the audio disappears is Zero Beat.

LO (Local Oscillator) Adjustment

The LO(Local Oscillator) trimmer capacitor must be adjusted, to allow the "Tune" variable capacitor to cover the correct frequency range, in this case 3.5MHz to 4.0MHz.

Cut the power to the SuperHet and install the 6SA7 tube.

This step is performed with power applied to the homebrew SuperHet and a high input impedance audio amplifier powered on and connected to the "Phones" connections on the BFO/IF Gain control panel.

Once the SuperHet is warmed up, perform voltage measurements at the socket of the 6SA7 tube. Compare these voltage measurements to the Approximate Voltages schematic. Troubleshoot if voltage measurements differ from Approximate Voltages schematic.

During this adjustment, the Tune variable capacitor's plates should be half meshed.

I set my Eico Model 324 Signal Generator to a 3.75MHz internally modulated AM signal, then clipped the yellow signal generator output lead to the top of the Antenna Coil. Sorry about the blurry picture.

I mounted the LO (Local Oscillator) trimmer capacitor to the Local Oscillator coil's tube socket, circled in the above picture. This trimmer capacitor is adjusted, until you hear a loud tone from the frequency generator. This sets the Tune capacitor to pickup signals at 3.75MHz. Now with the Tune variable capacitor's plates fully meshed my SuperHet should pickup signals at 3.5MHz. With the Tune variable capacitor's plates unmeshed, my SuperHet should pickup signals at 4.0MHz.

At this point, you can adjust the last trimmer capacitor, connected to the first IF transformer's input coil, for maximum volume. The trimmer is circled in the above picture.

Antenna Trimmer Adjustment

This step is performed with power applied to the homebrew SuperHet and an high input impedance audio amplifier powered on and connected to the "Phones" connections on the BFO/IF Gain control panel.

During this adjustment, the Antenna Peak and Tune variable capacitor's plates should be half meshed.

I set my Eico Model 324 Signal Generator to a 3.75MHz internally modulated AM signal, then clipped the yellow signal generator output lead to the top of the Antenna Coil.

The Antenna trimmer capacitor is also adjusted for maximum volume. This will allow the Antenna Peak variable capacitor to be adjusted for resonance between 3.5MHz and 4.0MHz.

Secure Wiring

The final assembly step of my homebrew SuperHet, was to secure the longer runs of wiring to the wooden base. I used tape to hold the wires in position while I applied a dab to E6000 clear adhesive to hold them in place. For shorter wiring runs, I just bent the wires into orthogonal positions, so that the wiring was pleasing to the eye.

Conclusion

My homebrew SuperHet was two years in the making. It took time to build the Helical Coil Winder, wind the required IF, BFO, Antenna, and Local Oscillator coils, and build the required cardboard shield enclosures while trying to work and maintain a family life. It was well worth it and I proud of my radio creation. This whole journey started with the book "The Impoverished Radio Experimenter Volume 5" which inspired me to build a SuperHet of my own.

As an addendum to this project, I will research how my homebrew SuperHet can be converted to the Standard AM Broadcast band (525kHz to1705kHz) as I typically cannot find much going on in the 80 Meter band (3.5Mhz to 4.0Mhz), this receivers intended frequency operation, day or night.

My Homebrew SuperHet in Action!

]]><![CDATA[Fisher MC-3020 Stereo Rebuild]]>Sat, 04 Jul 2020 23:13:59 GMThttp://www.radioboatanchorblog.com/blog/fisher-mc-3020-stereo-rebuild

I rescued this early 80s Fisher Model MC-3020 Stereo from our next door neighbor's garbage. Originally, its was his mother's and had been stored in her garage for many years. It came into my neighbor's possession when his mother passed away. The MC-3020 was known as an Integrated Component System, and incorporates a AM/FM Stereo Receiver, Stereo Cassette Player/Recorder, and a BSR made
3-Speed Turntable.

MC-3020 Problems

Upon initial power up, I found that my garbaged picked MC-3020 had the following problems:

Sound would only come out of the left speaker in AM/FM and Cassette player mode.
The Turntable Platter and Tone Arm would not move at all in Manual or Auto modes.
The Cassette Player played the cassette at slower than normal speeds. When you pressed the stop button the play button would launch into the air.
The Cassette Player counter did not move at all in play, fast forward, or rewind modes.

Disassembly

The first step is to completely disassemble the MC-3020. I started by removing the screws circled in red, these screws hold the chassis in place.

You must remove both the cassette player and turntable assemblies before removing the chassis. Four screws, circled in the picture below, hold the cassette player to the wooden cabinet.

You must detach this AC Choke from the chassis, using the screws circled in red, before removing the cassette deck assembly.

Carefully lift up the cassette player assembly and then disconnect all wiring to the the chassis. The cassette player assembly is then free and clear of the wooden cabinet and can be set aside for later servicing.

The chassis must be slid as far forward until an obstruction is felt. This will allow you to reach inside from the front to free the turntable from the wooden cabinet.

The turntable assembly is held in place on the underside by two clips, positioned diagonally from each other. You must reach in from the front of the wooden cabinet to remove them.

Disconnect the right and left Tone Arm audio connections from the back of the wooden cabinet, noting their color and position.

The turnable assembly can be removed, once the remaining electrical connection has been disconnected. At this point, the chassis can be remove from the wooden cabinet by pulling it forward.

Once removed from the wooden cabinet, I recommend propping up the turnable assembly on several 2x4 wood blocks, so that the mechanical undercarriage is not bearing the weight.

Chassis Switch and Control Cleaning

Upon initial testing, I discovered that the right audio output was not working on my MC-3020, I suspected the culprit was a dirty switch or mechanical control. As such, I decided to spray contact cleaner inside every mechanical control in the chassis then put them through the motion several times to clean up the contacts and the resistive elements the contacts may touch.

First I sprayed one Function switch deck.......

and the other Function switch deck.

Both decks of the Volume control.

And inside the remaining Balance, Treble, Bass, and the Recording Level controls. In addition, I sprayed contact cleaner inside the Tape Monitor, Loudness, Mode and Power buttons. Here is a picture of me spraying contact cleaner inside the Tape Monitor button. Don't forget to exercise the control after spraying contact cleaner into it!

Tuner Dial Lubrication

Like many stereos of the era, the MC-3020 uses a dial cord and pulleys to connect the Tuning Knob, Tuning Variable Capacitor, and Analog Dial Frequency Indicator together. While the chassis is out, it is a good idea to lubricate the shafts of each dial cord pulley . I use Labelle 107 Oil as it is safe on plastics and I have it around for my model train hobby.

Chassis Indicator Light Cleaning

The MC-3020 uses many incandescent bulbs for back lighting and for indicators. As the chassis is apart, it is a good idea to clean them using Windex and a lint free chamois.

Here is a "before" picture of the Tuner Dial Backlight bulbs, notice their dirty glass envelopes.

Here is a picture of the Tuner Dial Backlight bulbs after cleaning. Notice the difference?

In addition, I recommend cleaning the Tuner Dial Backlight enclosure as well.

With the Tuner Dial Backlight enclosure removed, you can access the back of the Tuner Dial Bezel for cleaning.

The Record and Stereo indicators use small light bulbs. I recommend cleaning these as well.

I recommend cleaning the Record and Stereo indicators light bulb enclosures as well using a Q-tip moistened in Windex.

The Recording Level Indicator meters can be removed from the chassis, allowing you to clean their meter faces.

Chassis Electrolytic Capacitor Replacement

As electrolytic capacitors age, their electrolyte dries up causing their electrical capacity to drop and leakage current to increase. It is definitely a good idea to replace 40 year old electrolytic capacitors like the ones in the MC-3020!

Electrolytic capacitors should be replaced with one of similar capacitance and equal or above Voltage rating. These type of capacitors are also polarized so make sure you observe the polarity of the capacitor to be replaced and install new the same way.

I check each replacement capacitor with my trusty GM328 Multi-Function Tester before installation.

I replaced electrolytic capacitors on one printed circuit board at a time in the chassis. In this case I am replacing the capacitors on the "AIN Power" board. I mark the replacement capacitors with a permanent black marker line on top to indicate they have been replaced as sometimes the original and replacement capacitors look very similar. The light blue one circled in this picture still needs to be replaced.

In many cases, new electrolytic capacitors of same capacitance and working voltage are much smaller that their older counterparts.

After the electrolytic capacitors on a printed circuit board are replaced, I test the chassis by connecting speakers, antennas for both AM and FM, then connect power and turn it on. You do not need to the connect the cassette deck or turnable assemblies for this step. Just turn the mode switch to AM or FM only. Notice that I did not replace one of the large capacitors on the AIN Power board. I will have to come back to replacing this capacitor as I did not have one with the proper capacitance and working voltage in stock. One of the first things I noticed was that sound was now coming from both speakers now. Looks like applying contact cleaner to the mechanical switches and controls in an earlier step resolved my right audio output problem.

Turnable Repair

As mentioned, the turntable platter and tone arm would not move at all in Manual or Auto modes when the MC-3020 was powered on. In addition, I could not remove the spindle or turn the platter by hand. My experience with turntables has shown me that the culprit is old grease that has decomposed into a glue like gunk. Your best weapon against grease turned gunk is heat. When applying heat to the spindle make sure you do not melt the rubber mat that covers the platter.

The platter bearing was seized as well. After removing the e-clip. I took the solder tip out of my 40 Watt Weller soldering iron then used the soldering iron to heat up the bearing, and by proxy the grease in it, until I could lift the platter off of its shaft.

After reapplying heat several times, the platter finally came off. This exposed the idler wheel, used to control the platter speed, the left and right tone arm audio connections to the chassis, and the tone arm gear.

I had to also apply heat to the tone arm gear using a solder gun, in order to thin the old grease, allowing it to be removed from the plinth or base.

Here's a picture of me using a Q-tip to remove the old grease from the platter shaft.

Time to lube things up on the top side of the plinth. After cleaning out the old grease, I applied Labelle 106 PTFE grease to the platter bearing before assembly. Labelle 106 is safe on plastics and I always have a tube of it due to my model train hobby.

The platter bearing sits at the base of the shaft.

Time to grease the track on the tone arm gear.

Time to oil the remaining components on the top side of the plinth. I put a drop of oil on the platter, idler, and tone arm gear shafts.

It is a good idea to put some grease on the gear at the base of the platter, before assembly.

An e-clip on the platter's shaft holds it in place. As you can see, I accidentally melted the platter's rubber mat during disassembly.

The aluminum BSR logo center just slips in and under the center of the rubber mat.

The aluminum outer ring that graces the platter's rubber mat fell off during disassembly. I had to scrape off the old adhesive then remove the residue with denatured alcohol.

I put E6000 all purpose adhesive on the back side of the aluminum outer ring.

Then I positioned the aluminum outer ring in place on the platter's rubber mat, and held it down with five D batteries, in order to help it adhere.

The back side of the plinth, or base of the turntable, has many mechanical joints that need to be oiled as well. I oiled each and every joint then ensured they moved freely.

The back side of the plinth also contains many gears that need to be greased. First, I cleaned off the old grease using a Q-tip dipped in denatured alcohol. Then, I applied new PFTE grease.

I Applied a drop of oil to the spindle and made sure all parts of it moved freely.

Time to test the turntable assembly. I made the proper electrical connections between the chassis and turntable assembly, then propped it up on several 2x4 blocks, making sure that the mechanical parts on the underside of the plinth were not obstructed.

Turntable Problem

After lubricating the turntable assembly, I had a curious issue in auto mode where the timing was off and the record would drop after the tone arm was already in position. I spent many evenings troubleshooting this issue, thinking that I either bent or assembled something wrong. On a whim, I decided to turn the spindle 180 degrees in its center mount of the platter. Like magic, everything started to work as expected with the record dropping first, followed by the tone arm moving into position. The spindle mount in the platter shaft has a notch, the spindle record dropping mechanism must align with this notch.

Cassette Deck Repair

The adhesive that held the cassette keys in place had grown brittle through the years. When I pressed the Stop key the Play key would launch into the air. I used E1000 adhesive to glue all keys back onto their metal mounts.

In order to get at the cassette desk mechanism and the electrolytic capacitors on the printed circuit board, you must remove it from its mounts. Three screws, circled in red, hold the printed circuit board to the cassette deck chassis.

I replaced all of the electrolytic capacitors on the printed circuit board with new.

There is also one electrolytic capacitor, circled in red, across the motor leads that needs to be replaced.

There is a switch on the printed circuit board that is triggered by the cassette keys, via its mechanism. Access to the contacts within the switch can be obtained through its end. I recommend spraying some contact cleaner into it, then exercising the switch manually, so that the contacts are properly cleaned.

In the cassette deck chassis, I put a drop of oil on all pulley shafts and then made sure each pulley spun freely.

I applied PFTE grease to any metal slides, after the old grease was cleaned away with a Q-Tip dipped in denatured alcohol.

The initial issue was that the cassette player played the cassette at slower than normal speed and the cassette counter did not work. I had determined this was due to deteriorated drive belts. I replaced both of them with new drive belts I had on hand. I purchase drive belt kits on eBay that contain a variety of lengths. Most of these drive belt kits come from China so it takes awhile to be delivered to my home in the United States. Purchasing a drive belt kit from China is a lot cheaper than purchasing the individual belts from an electronic parts distributor.

Time to attached the printed circuit board to the cassette deck chassis using three screws circled in the picture below.

Like the turntable assembly, I also test the cassette deck assembly out of the cabinet by connecting the proper electrical connections to the chassis, propping it up on 2x4 blocks then powering on the chassis. The cassette deck works a lot better now that the drive belts have been replaced.

Assembly

I treated the MC-3020's wooden cabinet, inside and out, to a coat of lemon oil. This is the best time to do it, with all of the electronics removed.

I then buffed the veneer with a lint free chamois.

Next, the chassis was reinserted part-way into the wooden cabinet from the front.

I placed the turntable assembly in place on top of the wooden cabinet, then connected the power connection to the chassis.

You must attach the turntable assembly's tone arm audio connections from the opening in the back of the wooden cabinet.

The two clips that hold the turntable assembly to the wooden cabinet can then be installed.

Time to install the cassette deck. First, I fastened the AC Choke to the chassis with two screws.

Then, I installed the electrical connector that connects the cassette deck assembly to the chassis.

The cassette deck assembly was once again fastened to the wooden cabinet with four screws circled below.

I noticed the cassette deck was running too fast after assembly. I drilled an access hole that allows me to use a small jewels screwdriver to adjust the cassette deck's speed easily from the outside while it is in play mode.

Finally, I replaced the screws that hold the chassis in place.

Conslusion

Getting this vintage Fisher MC-3020 sure required a lot of work! Actually, it is not work if you really enjoy what you're doing. I thoroughly enjoyed getting this vintage integrated component system up and running again. As you can see, it has a place in my "wall of stereos". I will enjoy listening to cassettes and records being play on it while I work on other projects.

My rebuilt Fisher MC-3020 Stereo in action!

]]><![CDATA[SHEJA JH-188 Chinese Radio Build]]>Thu, 06 Feb 2020 01:38:37 GMThttp://www.radioboatanchorblog.com/blog/sheja-jh-188-chinese-radio-buildI am continuing with the Chinese radio builds. This time, I will be building the Sheja JH-188 radio kit.

About the Sheja JH-188 Radio

The Sheja JH-188 is an FM only digital mono receiver kit that is commonly found on sites such as Amazon, eBay, Banggood, and Alibaba e-commerce web sites. I purchased mine from eBay for $7.69.

It is built around the CD9088 integrated circuit. The CD9088 is a Chinese clone of the TDA7088T, which was developed by Philips Corporation in the early 1990s.

The TDA7088T, and Chinese CD9088 clone, is a mono FM integrated circuit intended for use in battery operated pocket radios. With the CD9088, no specialized parts such as IF coils or ceramic filters are required, making the parts count built around this integrated circuit low. It has builtin tuning capability if used with an external Varicap BB910 diode. The CD9088 has builtin FM station scan and reset functions. In addition, it has all the necessary stages to process RF input from the antenna to audio output. The CD9088 can be operated with as little as 1.8 Volts DC.

SHEJA JH-188 Circuit Theory

Unfortunately, my JH-188 didn't come with assembly instructions or a schematic. If I would have inventoried this kit upon arrival, I would have noticed the missing assembly/schematic documentation. I was, however, able to find a picture of a schematic on a listing in Alibaba, and included it below. Note: The bottom schematic is an extension of the top one.

Based on my years of electronic experience, I'll try to extrapolate what the discrete components do in this circuit.

C3 - Possibly used to debounce scan reset switch SW2.

C5 - Used to debounce scan switch SW1.

BB910 and L1 - Varicap diode and coil used for the LC tank circuit used for tuning.

C4 - Decoupling or Bypass capacitor, shunts noise caused by other circuit elements to ground.

CD9088 - Integrated circuit used to convert a Radio Frequency(RF) modulated signal to Audio Frequency(AF).

SW3 and LH2 - Built in flashlight circuit.

SW2 - Switch clears all radio stations from memory.

SW1 - Switch used for radio station scan.

PL1 - Audio jack for ear buds. The ear bud wiring is also used as an antenna.

KW1A/B - Audio volume control and main radio power switch.

Q1 - Transistor used to amplify audio signal.

L2 - Possible RF choke, preventing Radio Frequency (RF) signal from entering the audio amplifier stage.

Packaging

My JH-188 came in an international mail envelope, direct from mainland China. The mail envelope contained a plastic bag with all of the radio's discrete components.

Inventory

It is important to inventory all parts, prior to starting the assembly process. Immediately reach out to the vendor if any parts are missing. If I had taken my own advice, I would have noticed that assembly instructions and schematic documentation were missing. I use an old plastic food container that contained a salad mix to contain all of the radio's parts so they don't get lost. A mistake in this picture is that I should have stuck the CD9088 integrated circuit and transistor, circled below, in anti-static foam to protect them from damage. You can wrap these components in tin foil if anti-static foam is unavailable. Granted, the supplier did not protect these components by sticking these component's metal leads into anti-static foam, but it is a good practice to get into.

Soldering

You will need a soldering iron with accurate temperature control and an ultra fine tip, in order to solder the surface mount CD9088 integrated circuit to the printed circuit board. I use the ZENY 862D+, which is a soldering / hot air surface mount rework station, available from many e-commerce vendors.

First, I soldered the surface mount CD9088 integrated circuit to the foil side of the printed circuit board. I started with this component as it was the hardest component to solder in place. It is easier to mount when no other components are already soldered to the printed circuit board.

I then tested all other components, using the Mega 328 Component Tester, before soldering to the printed circuit board. The Mega 328 can test resistors, capacitors, inductors, transistors, and diodes. It cannot, however, test integrated circuits such as the CD9088. I find that these inexpensive radio kits often have discrete components that are either out of tolerance of just simply defective. I replaced any defective or out of tolerance components with spare parts I had on hand.

Next, I soldered all ceramic capacitors and inductors in place. The rest of the components are of the thru-hole type, where the component is inserted from the component side and soldered on the foil side.

I then soldered the single resistor in place.

Next, I soldered the transistor and Varicap diode in place. These components are polarized, meaning they are have to be installed in the proper direction.

All three switches were then soldered in place.

The audio jack, volume control/power switch, and the incandescent light bulb were soldered in place. I placed plastic insulators around leads to the light bulb.

Finally, the wires that connect to the batteries were soldered to the foil side of the printed circuit board.

Testing

It is important to test the printed circuit board assembly before mounting it into the radio's case. I connected two AAA batteries to the power connection leads and the supplied ear buds to the audio jack. I then turned the volume control clockwise until I heard the click of the power switch then adjusted the volume control to mid point. Push the SW3 button should turn on the light bulb. Push SW2 should reset scan and then push the SW1 scan button until you hear a radio station. If you don't hear a radio station, check component placement and orientation.

Defluxing the circuit board

Solder contains flux, an agent which aids in the soldering process, but leaves a sticky brown residue behind. Before mounting the printed circuit board in the radio's case, I spray defluxer on the foil side, use a tooth brush to free any stubborn flux, then blow it off with compressed air to remove any residue and to completely dry it.

Look how clean the foil side of the printed circuit board looks after defluxing. At this point, I also soldered the battery connectors to the end of the wires. The spring terminal goes on the black wire while the plate terminal goes on the white one.

Final Assembly

Place the radio's front cover face down on a smooth surface and then install the Light, Reset, and Scan buttons.

With the radio's front cover still face down, place the printed circuit board foil side up in the top area of the radio case. Route the wires inside the case so they don't get crimped when the back cover is installed. Install the AAA battery terminals into the battery compartment. The battery terminals just slide in place into the provided slots.

Install the back cover and belt clip, secure with the single provided Philips head screw.

Now turn the radio over and install the silver plastic plate labeled "SHEJA JH-188" it just clips in place.

The knob for the power switch/volume control installs with a single Philips screw in the center. The knob is installed correctly if you hear the click of the power switch opening its contact when at the 8 O'clock position.

A chrome plastic cover clips in place over the top of the screw hole of the power switch/volume control knob.

Place two AAA batteries into the battery compartment then install the battery cover over it.

Radio Operation

Plug the supplied ear buds into the audio jack. Turn the volume control knob clockwise until you hear a click of the power switch then move until about mid point. Click on the Reset button, then click the scan button several times until you hear a station. Your radio is now complete!

Station Reception Issue

I noticed that during the testing phase I was picking up a lot more stations than after final assembly. I had determined that I was touching the positive battery lead during testing and my body was acting like a natural antenna. In order to improve radio reception, I connected a 2 ft long blue wire to the positive battery connection then routed the antenna through a small hole I drilled at the bottom of the radio cover.

Conclusion

Below is a picture of the finished SHEJA JH-188. At a price point of under $8, the JH-188 is a great little kit for a hobbyist or a STEM program. It can be used to teach soldering and assembly skills. However, because the JH-188 performs all signal processing using a single integrated circuit, this kit really does teach radio principals. In addition, the JH-188, even with the addition of an external antenna, lacks the sensitivity of most standard FM radios. The low sensitivity of JH-188 only make it suitable for serious radio listening in metropolitan areas were strong radio signals are present.

]]><![CDATA[HX-6B Chinese Radio Kit Build]]>Sun, 12 Jan 2020 16:23:43 GMThttp://www.radioboatanchorblog.com/blog/hx-6b-chinese-radio-kit-buildToday on Radio Boat Anchor, I am going to build the HX-6B Chinese Radio Kit, otherwise known as "the little blue one" by many electronic hobbyists. This kit can usually be found for a few dollars on many e-commerce sites such as Amazon, eBay, Banggood, and Alibaba. I purchased my HX-6B on a "buy it now" auction for $4.59. It shipped directly from China and three weeks later it arrived with my mail.

About the HX-6B Radio

The HX-6B is of standard Superheterodyne or "Superhet" radio receiver design. The Superhet radio design was invented by Edward Armstrong, an Electrical Engineer from the United States, in 1918. It has been used widely in analog AM and FM radio receivers for most of the 20th century until it was supplanted by SDR (Software Defined Radio) in which all single processing is done through code on a one or more integrated circuits. The HX-6B would make a great kit for an educational STEM program as it has all of the building blocks of a basic AM radio receiver. This kit is great for education purposes but will probably lack sensitivity as most AM radios of the Superhet type have two IF (Intermediate Frequency) stages where this kit is only designed with one IF stage. Station reception may not be a problem if you live in a metropolitan area were AM station signal strength is strong.

HX-6B Circuit Theory

The instructions you get with the HX-6B radio kit is primarily in Chinese. However, the schematic and parts list in the instructions are printed in english. In addition, the component side of the included printed circuit board has english destinations for the components. You can easily assemble this kit without the need to read Chinese. All of the circuit theory is written in Chinese, so I am going to extrapolate the circuit theory of the HX-6B, based on my 30 years of electronic experience.

Transistor V1 acts as a mixer between the incoming AM (Amplitude Modulation) modulated RF (Radio Frequency) signal and the LO (Local Oscillator) circuit. This producers a constant 455kHz AM modulated signal that is fed into transistor V2. Capacitor CA is the Tuning control and forms a tank circuit with T1, allowing the radio to pass a certain RF frequency while rejecting all others.
Transistor V2 is an IF (Intermediate Frequency) amplifier circuit. Transformers T3 and T4 "pass" the 455kHz signal and reject all others.
Transistor V3 is what is known as a "Detector", it strips the RF carrier signal from the AF (Audio Frequency) signal.
Transistor V4 is the AF preamp. Its purpose is to amplify the audio signal. Potentiometer RP is the volume control.
Transistors V5 and V6 form a Class A push pull amplifier, providing enough power to drive a 8 Ohm speaker or external headphones.
Typically radios have an AGC (Automatic Gain Control) circuit, this prevents radio stations from fading in and out during listening and giving a fairly stable audio level. I believe R3 and C5 might be an AGC circuit, but am not %100 sure.

Unpacking:

The HX-6B radio kit comes in a clear plastic wrapper. All of the components, including printed circuit board and instructions, are housed in the blue plastic shell of the AM radio.

As mentioned, the instructions are primary in Chinese. However, the schematic and parts lists are in English.

It's a good idea to inventory an electronic kit, such as the HX-6B Radio Kit, before assembly. Make sure all required parts are present and accounted for, before assembly. If any parts are missing, reach out to the vendor, before starting the assembly process, to acquire any missing parts.

I like to put all small discrete parts in a plastic container before assembly. That way they are all contained and it is less likely that I might lose one.

Assembly

When assembling radio kits, I usually do it in a certain order. First, I solder the resistors to the printed circuit board. Before soldering a resistor to the printed circuit board, I check its resistance value with my Mega 328 component tester. This handy device can check resistor, capacitors, diodes, transistors, and inductors. I often find resistor, capacitors, and inductors either defective or out of tolerance in these little kits. I don't believe they use "top shelf" components. I replace any components that are either defective or out of tolerance.

I solder each resistor, one at a time, to printed circuit board. This is a fun activity and I am in no real hurry.

Once a component is soldered to the printed circuit board, I cross it off of the parts list.

Finally, all of the resistors have been installed in the printed circuit board.

Next, I install the ceramic disk capacitors. Checking each one with my Mega 328 component tester before soldering to the printed circuit board.

Time to install the electrolytic capacitors. Once verified with the component tester, I solder them to the printed circuit board. Electrolytic capacitors are polarized. The negative lead side is denoted on the printed circuit board by a side half of the circle colored in white.

There are three types of NPN transistors included in this kit:

9013H (Quantity 2)
9014
9018 (Quantity 3)

Transistor type is printed on the flat side of each transistor.

As with other components, I check each one with my component tester before soldering to the printed circuit board. Note, transistors have three different connections, Collector, Base, and Emitter. It is important that you install the proper transistor into the proper holes in the printed circuit board. The locations are labeled on the component side. In addition, you must install them in the proper orientation. You must match the flat side of the transistor with the flat side of the label printed on the component side of the printed circuit board. See areas circled in the picture below:

All of the transistors are now installed.

I then installed the 5K potentiometer with built in power switch. This is labeled RP in the schematic and it will serve as the volume control. There was no way to test the potentiometer with my component tester. I just checked with my VOM (Volt-Ohm-Meter) that it measured 5K Ohms between the two outer leads of the potentiometer. You should see the resistance change from 0 to 5K Ohms or 5K Ohms to 0 if you place the meter leads between one of the outside leads and the center lead.

Next, I installed the audio transformer. I did some resistance checks with my VOM meter to determine if there were three windings, two should have a lower resistance while the third has more windings and should be slightly higher in resistance. The audio transformer must be installed into into the printed circuit board in the right orientation. If you look closely, there is a little raised bump on the bobbin of the transformer, this should line up with the white dot on the component side of the printed circuit board. See areas circled in the picture below:

The audio transformer is installed in the corner of the printed circuit board. In addition, I installed the oscillator coil and the first and second IF transformers. The oscillator, first, and second IF transformers slugs are color coded. You must install them in the proper locations.
T2: Red Slug (Oscillator Coil)
T3: White Slug (First IF Transformer)
T4: Black Slug (Second IF Transformer)

Time to install the audio jack, circled in the upper left-hand corner.

The next step is to install the variable capacitor, used for tuning, to the printed circuit board. The mounting screws used for the variable capacitor are also used to hold the nylon loopstick antenna mount in place.

The two screws provided secures both the loopstick antenna mount and the variable capacitor to the printed circuit board. You will need to solder the three variable capacitor connections to the printed circuit board.

The HX-6B has a Red LED (Light Emitting Diode) power indicator, circled in the picture below. It must be routed though the hole in the printed circuit board from the component to the foil side.

The LED is polarized, the flat side of the component corresponds to the side the arrow points to on the printed circuit board.

The loop stick antenna consists of two windings on a ferrite rod. The windings act like a step-up RF transformer. It is important to connect the wires to the right connections on the printed circuit board. As you can see from the picture below taken from the instructions, connections a and b connect to 100 wire turns while connections c and d are only 10 wire turns. It is easy to identify a and b connections using a VOM (Volt-Ohm-Meter) as the resistance between these connections are higher than between connections c and d.

The easiest way to make the proper connections from the printed circuit board to the windings is to lay it out as shown below.

Once all of the connections to the windings are made, it is time to slide the cardboard tube that secures the windings over the ferrite rod. Next, attach the ferrite rod to the printed circuit board using the nylon loopstick antenna mount. I also attached the dial to both the volume control and the turning capacitor, so that the radio is ready for alignment.

There are several places on the printed circuit board foil side that have broken traces. This is intentional so as to allow current checks of different stages of the radio. My recommendations is to just put a solder bridge across them as I found the current ratings listed in the schematic to be inaccurate. If you don't bridge these connections with solder, the radio will not work!

Time to attach the two provided blacks wires between the printed circuit board and the speaker. The yellow wire to the +3V point and the blue wire to the -3V point. I circled the points in red, on the sparsely populated component side of the printed circuit board, to show you where to make the connections.

On the ends of the yellow and blue wires, you must solder the battery contacts.

Soldering leaves sticky flux residue on the foil side of the printed circuit board. I spray flux remover on the foil side then use an old tooth brush to loosen the flux. I then use compressed air to blow away the flux residue and to dry the board.

Assembly

I found it easier to assemble the HX-6B radio in its case before performing alignment activities. Double-check the tightness of the screw that holds the dial to the tuning capacitor.

Place the tuning indicator sticker over the tuning dial. I recommend temporality placing the printed circuit board into the radio enclosure then rotating the tuning dial back and forth so that you can determine the proper dial indicator sticker placement.

Next assembly steps:

Lay the front half of the radio shell on a soft cloth.
Place speaker in as shown in picture.
Install printed circuit board as shown.
Secure printed circuit board with single provided screw.
Install battery clips, they simply press in the mounts.
Check tightness of screw that holds the volume control dial in place.
Apply several dabs of adhesive, such as E6000, to keep the speaker in place.

Install the batteries, the HX-6B radio is now ready for alignment!

Alignment

You must align a Superheterodyne receiver, in order to get maximum sensitivity and selectivity, and so that the tuning indicator indicates the correct station when being tuned.

Note: Do not use a regular screwdriver with a metal shaft to adjust transformer slugs and trimmer. It will skew your adjustment. It is best to use a non-metallic radio/TV alignment tool.

Note: If an RF Generator is not available, satisfactory results can be obtained by tuning into stations on the low and high end of the radio dial.

Here are the steps to align the HX-6B radio:

Turn on your RF Generator, set for a 530kHz carrier with AM (Amplitude Modulated) audio signal.
Place the lead of the RF Generator close the HX-6B's loop stick antenna.
Turn on the radio using the switch attached to volume control, adjust volume control midpoint.
Turn the HX-6B tuning capacitor fully counter-clockwise.
Adjust the red slug on the local oscillator transformer for maximum volume of the audio signal.
Adjust the white slug on the first IF transformer for maximum volume of the audio signal.
Adjust the black slug on the second IF transformer for maximum volume of the audio signal.
Set RF Generator for 1600kHz.
Turn the HX-6B tuning capacitor fully clockwise.
Adjust the trimmer on the tuning capacitor for maximum volume.
Repeat steps 1 through 10 so as to double check adjustments.
Turn off RF Generator.

Antenna Alignment

In order to further maximize the sensitivity of the HX-6B, you must adjust the antenna trimmer and loop stick antenna.

Turn HX-6B radio on using the volume control, adjust volume control midpoint.
Find a station midpoint on the tuning dial.
Adjust the antenna trimmer for maximum station volume.
Using an insulated tool, move the antenna coil back and forth along the ferrite core until maximum station volume is achieved.
Repeat steps 1 through 4 so as to double check adjustments.
Apply a dab of adhesive, such as E6000, to keep the antenna coil in place.

Conclusion

Below is a picture of the finished HX-6B. Simply install the back cover after the alignment process. At a price point of under $5, the HX-6B is a great little kit for a hobbyist or a STEM program. It can be used to teach basic radio principals, soldering, and assembly skills. However, with its only single IF stage, it lacks the sensitivity of most standard AM radios. The single IF stage makes the HX-6B only suitable for serious radio listening in metropolitan areas were strong radio signals are present.

The HX-6B in action

]]><![CDATA[Zeny F2C 2in1 862d+ SMD Rework Soldering Station Review]]>Sun, 27 Oct 2019 02:56:14 GMThttp://www.radioboatanchorblog.com/blog/zeny-f2c-2in1-862d-smd-rework-soldering-station-review

The Need

In addition to restoring antique radios, I also service household electrical and electronic devices. Recently, I serviced my Magnavox LCD Television, it needed an 8 pin surface mount EEPROM replaced and I didn't have the right tools to replace it. That is when I decided to invest in a SMD (Surface Mount Device) Rework Soldering Station.

The Zeny F2C 2in1 862d+ SMD Rework Soldering Station

The Zeny F2C 2in1 862d+ SMD Rework Soldering Station at the time of this writing was the cheapest combo hot air gun and soldering rework station on Amazon. At the time of purchase the price was $53.88. You could pay in excess of several thousand dollars for a good SMD rework soldering station and it might be worth it if you serviced printed circuit boards with SMD mounted components on a daily basis. I chose the inexpensive Zeny F2C 2in1 862d+ SMD Rework Soldering Station because as a hobbyist I rework printed circuit boards with SMD components on an infrequent basis. The Zeny F2C 2in1 862d+ SMD Rework Soldering Station boasts the following features:

Independent control of hot air gun and soldering iron.
Uses control circuitry to accurately maintain heat of hot air gun and soldering iron.
Hot air gun and soldering iron are fed by a low voltage DC power supply.
Rapid warm up of soldering to selected temperature.
Hot air gun rapidly comes up to prescribed temperature then cools when put into cradle.
Hot air gun includes four tips sizes to accurately direct the heat only at the required component(s).
Soldering iron comes with six different tips including a micro tiny tip used for SMD rework.

Note: This SMD rework station displays temperatures only in Celsius, there is no switch to change to Fahrenheit.

There is a person who claims you can add a jumper inside this workstation to change it to display in Fahrenheit. I will include the link to this later in this blog.

Unpacking

Zeny F2C 2in1 862d+ SMD Rework Soldering Station comes in an individual box only slightly bigger than the rework solder station itself.

This rework solder station comes with an instruction manual, four hot air gun tips of various sizes, six soldering iron tips of various sizes, some sort of tool with wire ends that I am not sure what it is used for, and the manual. The manual attempts to instruct you on the operation of Zeny F2C 2in1 862d+ SMD Rework Soldering Station. In my opinion, you're better off watching YouTube videos covering operation of this rework solder station. I think you will find them more useful.

Top view of the rework solder station before I lift if out of its box. The black cable to the right is attached to the hot air gun. Unlike the soldering iron, the hot air gun is permanently connected to the rework solder station. There is not connector that will allow you to detach it.

Here are all the discrete parts in the package. The solder iron stand (blue rectangular object and to the right) is supposed to include a tip cleaning sponge. It is noticeably missing. The hot air gun holder (black plastic piece in the center) needs to be mounted to the rework solder station cabinet before operation. The rework solder station senses when the hot air gun is in the cradle and turns off the heating element, leaving the fan on until it has sufficiently cooled.

Quality Control Check

I like to perform a quality control check on dubious branded electronic equipment from China before initial operation. This equipment is typically well designed but hastily assembled. The first step is to remove the machine screws on both sides that holds the cover in place.

The company "ZENY" that assemble this rework workstation uses some sort of red adhesive to keep the wire connectors firmly attached to the main printed circuit board.

During assembly, they never applied heat to the heat shrink tubing that covers the high voltage AC connections.

This was an easy fix.

I didn't like how they soldered the two ground connections together. They soldered the second ground connection to the first in order to save a lug.

I fished out another solder lug from my junk drawer then soldered the second ground connection to it. I then fastened it back down using one of the screws that holds the step-down transformer in place.

There were no other issues with my rework solder station. I went ahead and reattached the cover then installed the hot air gun holder.

This is how the holder looks with the hot air gun in place.

Some buyers complained that the ceramic heating element in the soldering iron did not make good contact with the solder tip, causing poor thermal heat transfer, this was not the case with the solder iron that was included with my rework solder station.

The soldering iron connects to the rework workstation with a screw on connector and can be easily replaced.

Electrical Testing

I like to perform an electrical test on dubious branded electronic equipment from China before initial operation. The first checks was to measure AC Volts between the rework solder station cabinet and a grounded electrical socket. I did this in my basement bathroom as it has an AC outlet that is most easily accessed. Note to self, install a GFE outlet in basement bathroom in the future. The multimeter measured 2.5 Volts AC between rework solder station cabinet and the electrical socket ground. This is within safe levels.

The next test was measuring AC Volts between the metal tip of the hot air gun in holder and the electrical socket ground. The measured voltage was 0 Volts AC, very good!

The next test was measuring AC Volts between the metal tip of the hot air gun out of holder and the electrical socket ground. The measured voltage as 1.8 Volts AC, this is acceptable.

I measured AC Volts between the metal tip of the soldering iron and the electrical socket ground. The measured voltage was 38.1 Volts AC, this seemed a little high and it concerned me.

Until I performed the same electrical testing on another temperature controlled soldering iron and found it to be close to 30 Volts AC as well.

In use

Zeny F2C 2in1 862d+ SMD Rework Soldering Station's soldering iron worked great on soldering a surface mount integrated circuit on the printed circuit board of radio kit I purchased from e-bay.

In addition, I was able to replace this surface mount 8 pin EEPROM in my Magnavox LCD Television using this rework soldering station. Using smallest tip I was able to direct the heat of the hot air gun on the pins of the surface mount integrated circuit then lifted it off the board with tweezers. I was able to dial in the soldering iron temperature where it had just enough heat to solder the surface mount integrated circuit back onto the printed circuit board without damaging the component or the board.

Conclusion

The Zeny F2C 2in1 862d+ SMD Rework Soldering Station would be a great asset to any hobbyists' workbench who has the occasional need to do rework of surface mount printed circuit boards. The integrated soldering iron with multiple tips can replace your current workbench soldering iron.

Youtube Video 862D+ Celcius to Fahrenheit conversion

]]><![CDATA[Home Brew Helical Coil Winder Jig]]>Sat, 24 Nov 2018 16:46:36 GMThttp://www.radioboatanchorblog.com/blog/home-brew-helical-coil-winder-jigOne of my hobbies is building radios from scratch. I construct them in bread board style fashion. So far my "home brew" radios have all been of regenerative type that require few custom made coils that have 50 turns or less.

My next project is a Super Heterodyne receiver with custom built 400 KHz IF (Intermediate Frequency) transformers. Each IF transformer will require two 620 turn helical coils wound on a cardboard form. This project will require two IF transformer plus a LO (Local Oscillator) coil for a total of five helical coils. As you can see, a Helical Coil Winder Jig will come in handy for this project.

Below is a picture of the finished Helical Coil Winder Jig in action:

Step1: Main Body Construction

I started with a miniature crate I purchased from a local craft store. Woodworking is not one of my strong skills so I always try to start with a finished wood product then modify it for my needs.

I then cut the crate down to size using a jigsaw. The smaller piece to the right in the picture below will be used as the body of my Helical Coil Winder Jig. The rest of the crate will be broken down into its discrete pieces and used in this project.

The end piece from the unused part of the crate was nailed in place to form a small box 4 1/2 x 5 x 6 Inch in size. The nail holes were filled in with wood putty. The wood putty will be sanded down in a later step.

3/8 Inch holes were drilled for the main shaft using a drill press. The holes were drilled approximately 7/8 Inch from the top and centered horizontally.

The surface of the crate was rough. I used an orbital sander with fine grit sandpaper to smooth all surfaces and to remove excess wood putty.

Step2: Main Axle Construction

The main axle is made from a 3/8 Diameter 24 Inch Aluminum Rod. I drilled/tapped a hole on one end. A 10-32 x 4 Inch long screw will serve as the crank handle.

The 10-32 x 4 Inch screw is threaded into the aluminum rod until the head is almost flush with the rod. I then secure it in place with a lock washer and 10-32 nut.

I use a vise to bend the screw 90 degrees in order to form the crank handle. The bend starts about 1 1/4 Inch away from the 10-32 nut.

A 7/8 Inch Diameter dowel is cut down to 1 1/2 Inch and a hole is drilled down the center. This will serve as the crank handle. The hole down the center has to be just big enough to allow the dowel to move freely on the screw without binding.

Step3: Coil Arms Added

Two 10 inch x 1 1/2 arms were made from scrap pieces of the miniature crate then nailed to the base of the main body, flush with the bottom. These arms will hold the copper wire spool.

Here is a picture with both arms nailed in place.

Once again, wood putty was used to cover the countersunk nail heads.

Step4: Counter Added

My Helical Coil Winder Jig will incorporate an electronic counter, in order to keep track of the number of turns of wire, on the coil form. I created a small 2 Inch x 1 1/2 Inch arm to hold the counter. It is nailed to the side of the main body with it pointing up at a 35 Degree angle. Again, wood putty was applied to hide the countersunk nail holes.

The base of the electronic counter was temporarily mounted for fitment. Two small brass screws will hold it in place.

Here is what the electronic counter will look like when it is finally mounted. The counter runs on a watch battery and does not require external power.

The green and yellow wires coming out of the back of the electronic counter are soldered to the printed circuit board inside. Each wire is soldered to a point on the printed circuit board so that I can emulate the count button being press externally.

The green and yellow wires are soldered to a reed switch that will be triggered by a magnet.

The fragile reed switch is encased in heat shrink tubing for protection.

The magnet will be attached to the axle with the reed switch nearby so that the count on the electronic counter is incremented with each turn.

Step5: Coil Holder Construction

I needed a way to hold a variety of different size tubes on the axle during the coil winding process. I established that a cone shape would work best to hold the tubes centered on the axle. Once again a trip to our local crafts store yielded these small bird houses with 3 Inch diameter conical roofs.

A few swift hits of hammer removed the bottom part of the bird houses, leaving only the conical roofs. The rope hanging loops on top were cut off.

3/8 Inch diameter holes were drilled through the centers so that they could be threaded on the axle.

I reinforced the base of each cones with a generous amount of wood glue.

Step6: Protect the Wood

The main body of the Helical Coil Winder Jig was treated to two coats of Minwax Water-Based Semi-Gloss Polyurethane. I use semi-gloss because it is better at hiding imperfections than gloss. Water-based Polyurethane is much easier to cleanup and does not smell as bad as oil-based. Once dry, I lightly sand the pieces with fine grit sandpaper in between coats.

The conical coil holders are also treated to two coats of Polyurethane.

Even the hand crafted wooden knob received two coats of Polyurethane!

Once dry, all the holes in the main body where reamed out with a drill to remove residual Polyurethane that dripped in them during the coating process.

Step7: Final Assembly

A circular magnet was attached with Super Glue to one of the Drill Stop Collars. The magnet was attached opposite of the set screw.

I expanded the center hole in three 1 1/4 inch fender washers to 3/8 diameter so that I could slide them on the axle.

The Drill Stop Collar with the magnet attached was first threaded on the axle and cinched down about an inch from the crank handle. Next, a fender washer was threaded onto the axle. The axle was then threaded through the first hole in the main body.

Then another fender washer was threaded on the axle followed by a spring, fender washer, and another Drill Stop Collar. Finally, the axle was threaded through the other hole in the main body.

The the spring was compressed, then the second Drill Stop Collar to be threaded on the axle was cinched down. This assembly will keep tension on the axle and prevent it from moving backwards when you remove your hand from the crank.

The electronic counter was then attached to the main body. I used hot glue to keep the reed switch in close proximity to the circular magnet attached to the Drill Stop Collar. In addition, the hot glue was used to secure the wiring to the side of the main body.

Time to test the electronic counter, first I press the small silver button to set the counter to zero. Then I rotated the crank four times to made sure the counter reflected the correct number of turns.

Two more 1 1/4 fender had their center holes expanded to 3/8 diameter so that they would slide on the axle. I then mounted them to the base of each conical coil holder with two wood screws.

Automotive hose clamps will hold the conical coil holders in place on the axle.

A second 3/8 Diameter 24 Inch Aluminum Rod is threaded through the two coil arms. This rod will be stationary and hold the copper wire spool. The rod is held in place by two decorative hinges I had left over from another project. Two brass screws hold the hinge to the coil arm. I drilled a hole through the other part of the hinge then through the aluminum rod. A 1 Inch 4-40 screw holds the rod securely to the hinge.

The rod was also secured to the other coil arm in the same fashion.

Step8: Coil Winder in Action!

The conical coil holders can be used in various ways to hold a coil form. Below is the coil form configuration I use when only one side of the coil form is open. I did have to drill a 3/8 hole in the center of closed end in order to thread it onto the axle.

I use the conical coil holders in the following fashion when the coil form is open on both ends.

Typically, I drill two small holes then thread the copper wire through the holes at the starting end.

Before I start winding the coil, I click on the small silver reset button to zero the counter.

When winding the coil, I pinch the copper wire between my thumb and index finger to keep tension on it. You may want to wear gloves as this could cause a blister to form on your finger and thumb tips.

As you start winding the coil you may notice small gaps in the windings. While keeping tension on the copper wire, use your other hand to push the windings together to remove the gaps.

When I get to the proper amount of turns, I place a piece of masking tape on the end to secure the copper wire. Failure to do so will cause your coil to loose tension and unwind. I then use a bead of E6000 clear adhesive to keep the copper wire in place. I typically run beads of E6000 clear adhesive at 0, 90, 180, and 270 degree positions of the tube.

Finally, I use my Mega328 Component Tester to check the Inductance of my newly wound coil. The Inductance should be close to coils with the same number of windings on the same diameter coil form.

Conclusion

You should consider building my Home Brew Helical Coil Winder Jig if you find the need for creating numerous homemade coils for your electronic hobby projects.

]]><![CDATA[General Electric T1284A AM/FM Radio Remodel]]>Mon, 02 Jul 2018 18:30:25 GMThttp://www.radioboatanchorblog.com/blog/general-electric-t1284a-amfm-radio-remodelA friend of the family gave me this GE T1284A AM/FM tabletop radio. She knew that I restored old radios and thought I would like this one.

The T1284A is unremarkable and is of very common design for a radio from the mid to late 1960s. It is of superheterodyne (superhet) design with an AM IF (Intermediate Frequency) of 455kHz and an FM IF frequency of 10.7 MHz.

It is powered from 117 Volts 60Hz line current, common in the United States, and uses a transformerless design that incorporates a wire-wound resistor to step down the voltage and and a single diode to rectify the current required to power the transistor circuits.

The T1284A incorporates eight transistors, one being of the power transistor type housed in a metal case, that drives the speaker. The audio stage uses a 4 ohm PM (Permanent Magnet) speaker driven by an audio impedance matching transformer.

As unremarkable as this radio was, it did have a handsome wood cabinet and a pretty facade, which motivated me to take this radio on as a remodel project.

Step 1 Disassembly

The first step of any remodel project is to tear down the radio to see what you have to work with. The back cover is the disassembly starting point for the T1284A, one screw, circled in red in the picture below, holds it in place. The back cover fits in a slot, simply pull the back panel down and then straight up to remove.

Below is a picture of the inside of the T1284A.

The Volume, Tone, and Tuning knobs need to removed from the T1284A. They just pull off.

In addition, the AM/FM and AFC switch covers need to be removed.

Two screws, accessible from the back, hold the chassis in place inside the wooden cabinet and need to be removed. There is one in the upper right-hand corner of the cabinet.

The other is located in the upper left-hand corner of the cabinet.

Once the chassis screws are removed, you can tilt the front panel with attached chassis down.

The audio transformer is attached to the bottom of the cabinet. You must first unwind the wire leads from around the transformer in order to gain access to the screws holding it to the cabinet.

Remove the two screws that hold the audio transformer to the base of the cabinet.

You should now be able to pull the back panel through the front of the wooden cabinet. The chassis/front panel and back panel should now be free of the cabinet.

Step 2 Electrolytic Capacitor Replacement

As electrolytic capacitors age, their electrolyte dries up causing their electrical capacity to drop and leakage current to increase. It is definitely a good idea to replace 50 year old electrolytic capacitors like the ones in the T1284A!

Electrolytic capacitors should be replaced with one of similar capacitance and equal or above Voltage rating. These type of capacitors are also polarized so make sure you observe the polarity of the capacitor to be replaced and install new the same way.

I check each replacement capacitor with my trusty GM328 Multi-Function Tester before installation.

The electrolytic capacitors, circled below, were replaced.

One electrolytic capacitor, that was close to the front panel, had to be soldered to the bottom of the printed circuit board. I was able to get the original out but was unable to thread the replacement through the holes in the printed circuit board from the component side.

Here is a picture of all of the electrolytic capacitors that were replaced.

Step 3 Cleaning and Lubrication

The Volume control caused static to be heard from the speaker while be rotated during initial testing. As such, I decided to spray contact cleaner inside both the Volume and Tone potentiometers then rotate them back and forth several times to clean up the contacts and the resistive element the contacts touch.

Both the exterior and interior of the wooden cabinet were treated with lemon-oil base furniture polish.

Mr Clean MagicEraser sponges work miracles on cleaning vintage electrical cords! I apply an Armor All like protectant to the cord after it has been cleaned and dried.

Volume, Tone, and Tuning knobs are cleaned with a toothbrush and water then throughly dried.

No amount of metal polish is going to clean up the AM/FM and AFC switch covers. Their chrome finish is pocked and badly corroded. They will have to be painted.

I used Windex to clean the front panel including the speaker grill. Windex is my go-to universal cleaner.

Q-tips moistened with Windex work great for cleaning crevasses and hard to reach corners.

Look how dirty the paper towel was, just from cleaning the front panel.

I took this opportunity to lubricate the shaft of the Volume and Tone controls as their rotation was very stiff. I use Labelle 107 Oil as it is safe on plastics and I have it around for my model train hobby.

I also lubricated the shaft of the Tuning control.

In addition, I lubricated the Tuning control shaft on the back side of the front panel that connects to the variable capacitor and Tuning dial via a dial cord.

Step 4 Prep and Paint

I am going to paint several things on my T1284A:

AM/FM, AFC Switch Covers
The outer border of the front panel
The silver ring on each knob

The AM/FM, AFC switch covers were wet sanded with a 800 grit sandpaper to smooth out the surface and remove the pock marks due to corrosion.

I mounted the AM/FM, AFC switch covers to the end of Q-tips then degreased their surface with Prep-All. They are now ready for paint.

Two coats of silver paint and the switch covers look like new!

The first step on painting the outer border of the front panel is to mask off everywhere you don't want painted. I use a product called Frog Tape and brown paper to mask off the areas to be painted. Frog Tape has something called PaintBlock which makes crisp lines between painted and unpainted areas. I then degrease the surface to be painted using Prep-All.

Two coats of silver paint were applied to the area of the outer border.

Here is the finished product, once the Frog Tape and brown paper have been removed.

A lot of vintage radios I restore had painted accents on the knobs that have worn off due to normal wear/tear. I have tried to hand paint the accents but my hand is not steady enough and they look "amateurish".
I came up with a new way to paint the accents using a Sharpie Paint Pen and a drill. I mount the base of the knob in the drill and then apply the paint pen while the knob is spinning.

The results look very professional!

Step 5 Assembly

Time to mount the chassis/front panel back into the wooden cabinet. You will need to thread the back panel through the front of the cabinet first.

Time to install the two screws that hold the chassis/front panel to the cabinet. There is one screw on the left-hand side.

Another screw needs to be installed on the right-hand side.

The audio transformer was reattached to base of the cabinet with two screws.

I wrote the model number with permanent marker on the back of the heat sink attached to the chassis.The original sticker on the back panel that held this information had been bleached out by the sun and was unreadable.

During assembly, I noticed that the nut that holds the earphone jack on the back panel was rusted.

I treated the nut to a coat to silver acrylic enamel paint I had on hand for my model railroad hobby.

Time to reattach the back panel. A single screw on the bottom holds it in place.

The AM/FM and AFC switch covers were reinstalled.

I noticed some grime around the holes where the Volume, Tone, and Tuning controls protrude from the front panel. I used a Windex moistened Q-tip to clean.

Finally, I installed the Volume, Tone, and Tuning knobs. Here is the final result.

My General Electric T1284A AM/FM Radio in Action!

]]><![CDATA[Hallicrafters S-72 Battery Box Construction]]>Mon, 19 Mar 2018 01:19:43 GMThttp://www.radioboatanchorblog.com/blog/hallicrafters-s-72-battery-box-constructionIn a previous blog on radioboatanchor.com, I restored a Hallicrafters S-72 portable receiver. Here is a before and after picture of my S-72.

Click on the button below to visit my blog about rebuilding my Hallicrafters S-72.

Hallicrafters S-72 Portable Receiver Rebuild

What made the S-72 "portable", besides the carry handle, is that it could be operated under battery power. I am not talking about a 9 Volt or two AA batteries, this radio had a compliment of eight miniature tubes which required a 90Volt "B" battery for the tube's anodes and a 7.5Volt "A" battery for their filaments. A battery pack was designed to combine the A and B batteries into one convenient package. In the picture below, the empty area behind the chassis is where the battery pack was installed, a black cloth strap held it in place.

Below is a list of compatible battery packs for the S-72, straight out of the manual. Your local hardware or DIY store will not have them as these battery packs have not been produced since the 1960s!

Below is a picture of the completed S-72 battery box, which will replace the original battery pack. I will be wiring 9 Volt batteries in series to simulate the 90 Volt DC "B" battery. In addition, I will be wiring several D batteries in series to simulate the 7.5 Volt DC "A" battery.

Battery Box Contruction

I started out with this 15 Inch mini wood crate I purchased from a local crafts store.

Mini wooden crates on Amazon!

I partially disassembled the mini wood crate. With some carefully placed cuts I was able to reduce the crate's overall dimensions to 2.75 in x 11in x 5.25in. This was approximately the size of the original S-72 battery pack. I used finishing nails and wood glue to hold the new structure together.

Time for a quick check to ensure the new battery box fits into the S-72. Looks like it is a perfect fit!

I was able to reuse a scrap wood piece I cut off the original mini wood crate to fabricate a hinged top piece. This hinge piece is required to ensure the structural integrity of the battery box as it is being strapped down to hold it in place inside the cabinet. It is hinged so that you can easily access the batteries inside. The tiny brass hinges, screws, and hasp were all acquired at a local crafts store.

The S-72 chassis connected to the original battery pack using a single connection. I found that a standard octal tube socket mates perfectly with the S-72's connection. Here I used two pieces of scrap wood from the crate to fabricate a mount for the octal tube socket. The wood pieces are held in place with finishing nails and wood glue.

Tube sockets on Amazon!

A leftover hinge and brass screw reinforce the octal tube mount from the inside of the battery box.

I will be connecting ten 9 Volt batteries in series for the 90 Volts DC "B" battery. The batteries will be aligned facing up for easy access to their terminals.

I am using a wooden paint stirrer, cut to the proper length, to hold the 9 Volt batteries in place. At each end, I bent a solder lug in order to form a make-shift right-angle bracket. The right-angle bracket can be adjusted slightly then tightened down to form a tight fit against the 9 Volt battery cases.

We only need five "D" 1.5 Volt batteries wired in series to achieve the required 7.5 Volts for the "A" battery. I have mounted three twin D battery holders, one battery slot will not be used. I also added a 9 Volt battery holder, circled in red. This will hold an extra 9 Volt battery connected in series to boost the B battery voltage back up to 90 Volts DC as the 9 Volt batteries start to drain.

The nail-gun countersunk the finishing nails I used to assemble the battery box. I used wood putty to conceal their holes.

I used an orbital sander with fine (150 grit) sandpaper to sand the wood putty flush with the wood and to smooth out the rough cut wood used in the original mini wood crate.

I also used the wood sander to sand smooth the hinged tops and to remove the labeling on the wooden paint stirrer used to hold the 9 Volts batteries in place.

Here is a picture of the battery box parts after sanding.

I then treated all wooden battery box parts to two coats of water based polyurethane, followed by light sanding and then a final coat.

As mentioned, the 1.5 Volt D cells must be connected in series in order to achieve the required 7.5 Volts DC for the "A" or filament power supply. I wire the D cell battery holders in series except for the one slot, circled in the picture below, that will not be used.

The eleven 9 Volt battery clips are connected in series. While ten fully charged 9 Volt batteries in series will achieve 90 Volts DC, I included an extra battery clip to introduce another battery in the circuit to boost the voltage back to around 90 Volts as the 9 Volts battery's voltage drops as they discharge. This eleventh battery clip is jumpered when fresh batteries are used.

I used a gold paint pen to label each 9 Volt battery clip.

I attached rubber feet to the side of the wooden paint stirrer that comes in contact with the 9 Volt batteries.

This will prevent the batteries from shifting sideways in their mount.

Time to wire the octal tube socket I am using as a female connector. I plugged the male connector from the S-72 chassis into the tube socket in order to determine the proper connections for 90 Volts DC, 7.5 Volts DC and Ground. For reference, here is how the the male connector from the S-72 chassis is wired.

Time to mount the octal tube socket used as a connector to the battery box.

Here is a picture of the battery box with 9 Volt and 1.5 Volt D cells installed. Eleven 9 Volt batteries are installed as they are older batteries and their Voltage is dropping under load. Five D cells are installed with one battery slot left open.

Batteries on Amazon!

Time to test before installing the battery box into the S-72. I first test for the "B" battery voltage, which should be around 90 Volts DC.

Then I test for the "A" battery voltage, which should be around 7.5 Volts DC.

Time to do some initial testing, I already had my S-72 chassis out of the case for cleaning. This made it easy to connect the chassis to the battery box. After a brief warmup, the S-72 sprung to life and I could immediately hear a local sports talk station in the standard AM broadcast band.

Note, the plug on the line cord must be plugged into the chassis, in order to run on battery power. See area circled in the picture below.

After the S-72 chassis was once again safely installed in the cabinet, it was time to install the battery box. Once the battery box is in place, you secure it with the black cloth strap built into the cabinet. You must also connect the chassis to the battery box. The connection point is circled in the picture below:

A final test is to see if the S-72 cabinet side door closes properly with the custom battery box installed. Looks like it is a perfect fit as the side door closed and latched properly.

Finally, here is a picture of the finished product!

Here is a video of my battery powered S-72 in action!

]]><![CDATA[Hallicrafters S-72 Portable Receiver Rebuild]]>Sat, 10 Mar 2018 23:54:33 GMThttp://www.radioboatanchorblog.com/blog/hallicrafters-s-72-portable-receiver-rebuildBelow are before and after pictures of the chassis of my Hallicrafters S-72 Portable Receiver. I think you'll agree that my rebuild was a complete success!

About the Hallicrafters S-72

The S-72 is a Superheterodyne radio receiver built by Hallicrafters and sold from 1949 to 1953. This model covered the standard AM broadcast band. In addition, it covered three shortwave bands with continuous coverage from 540Khz all the way up to 30Mhz.

An internal loop antenna was used for standard AM broadcast band reception while a telescopic whip antenna is used for shortwave reception.

This radio employs eight miniature tubes and one Selium rectifier.
Here is the miniature tube compliment:
1T4, 1U4, 1R5, 1U4, 1U4, 1U5, 1U5, 3V4

The S-72 has an RF Amplifier, Mixer, Two IF (Intermediate Frequency) Amplifiers, Detector, and Audio Output stages. These stages are common in most AM radio receivers. In addition, it has a BFO (Beat Frequency Oscillator) for CW (Continuous Wave) or Code reception. Band change is accomplished by a four position selector switch that connects in different LC resonant tank circuits in the RF Stage.

Controls of the S-72 are fairly common, it has a Tuning, Band Spread, Band Selector, and On-Off Volume controls. The Voice-Code controls wether the BFO is on for Code reception and the frequency of the oscillator. There is also a "phones" jack for listening in noisy areas.

Powered could be derived from a dry cell battery pack. You have to insert the line cord plug into a receptacle located on the chassis to run on battery power.

The S-72 could also be powered from 105 to 125 Volts AC or DC line power as apparently direct current was still used in some areas.

The S-72 electronics were housed in a portable luggage style cabinet with a carry handle on top. I am not sure if "portable" is the proper term given that it weighs a whopping 16 pounds without the battery pack!

Access to the controls and dial is achieved by opening of the top cover. Access to the battery, line cord, and electronics is done through a side cover.

The S-72 retailed for $109.95 the first year of sale (1949).

Before pictures

The inside of my S-72 was in pretty good shape, although very dusty. All the vacuum tubes were in place and the two air capacitors, one for tuning the other for band spread, looked like they didn't have any bent plates. The empty area in the bottom is where the battery pack is housed. The black strap in cinched down and keeps the battery pack from moving around during transport. A single plug connects the battery pack to the chassis.

As you can see from the picture below, the faceplate, knobs, and whip antenna are missing from my S-72. The chassis was hastily put in place inside of the case and the two nuts that hold it in place were missing.

The external phone jack was just floating freely inside the case. See area circled in the picture below.

The manual, including schematic and alignment instructions, for the S-72 can be obtained from radiomuseum.org at no cost. Click on the button below to go to the web page.

Hallicrafters S-72 Manual

"Old Time Radios! Restoration and Repair" book on Amazon

I consult this book often during radio restoration. I grew up in the transistor and diode era and this book taught me a lot about vacuum tube and selium rectifier technology.

Step 1 Chassis Removal

As mentioned, just two bolts hold the chassis in place. The nuts that secured the chassis to the inside of the cabinet were missing from my S-72.

Here is a picture of the bottom of the chassis. The discrete parts (resistors, capacitors, transformer, coils) are dirty but in fairly good condition. Notice the blackened area in the lower left area of the chassis. It looks like there might have been one or more component failures in this area. I will need to investigate the components carefully in the blackened area before ever applying power.

Step 2 Chassis Cleaning and Lubrication

Contact cleaner was applied to all of the Band selector's contacts. I then moved the selector to all four positions in order to clean the contacts.

I applied Labelle 107 Oil to the shafts of all dial indicator pulleys. I have this oil on hand due to my model train hobby. This oil will will not harm plastic components.

In addition, I applied this oil to the shafts of the Tuning, Band Spread, Band Selector, On-Off Volume controls and Voice-Code controls.

Labelle 107 Oil was also applied to the shafts of the Tuning and Band Spread Variable Capacitors.

Labelle 106 Grease was applied to the bearing located to the front of the Tuning and Band Spread Variable Capacitors.

Labelle lubricants on Amazon

I use Labelle oil and grease for my radio restoration projects. I already have these products around as I am also a model railroad enthusiast. These products will not harm plastic.

The exterior of the chassis was cleaned with paper towels moistened with Windex glass cleaner. I use Q-Tips moistened with Windex to get into hard to reach places.

Step 3 Check Vacuum Tubes

Unlike semiconductor transistors that have a near infinite lifespan, vacuum tubes age and become less efficient. In addition, their filaments burn out rendering them inoperable. It is always a good idea to test all vacuum tubes in a radio you are servicing before doing any more troubleshooting.

In addition, make sure that that the right tube is in the right socket. This will save you troubleshooting time later.

Pictured below is my Eico Model 635 Vacuum Tube Tester testing a tube from the S-72.

Step 4 Electrolytic Capacitor Replacement

As electrolytic capacitors age, their electrolyte dries up causing their electrical capacity to drop and leakage current to increase. It is definitely a good idea to replace 65 year old electrolytic capacitors like the ones in the S-72!

Step 4a - Restoring the Multi-Section Capacitor

Multi-section capacitors, which were aluminum cans containing several discrete capacitors all connected to a common ground, were popular in the 1950s. There were used mostly in the power supply sections of vintage electronic devices. You can purchase replacement multi-section capacitors but they are expensive. I typically rebuild them by replacing their guts with inexpensive discrete capacitors of the same or slightly greater capacitance and working voltage. The multi-section capacitor in the S-72 is circled in the picture.

The multi-section capacitor in the S-72 contains the following discrete capacitors:

Capacitor A 60uF @ 150Volts
Capacitor B 20uF @ 150Volts
Capacitor C 20uF @ 150Volts
Capacitor D 2000uF @ 15Volts

The components connected to it's base terminals, circled below, must be desoldered before removing it from the chassis. I labeled each connection during the desoldering process.

The phenolic base is held in place with two rivets, they must be drilled out. Later, they will be replaced with machine screws, lock washers, and nuts.

Here is a picture of the multi-section capacitor removed from the chassis. The four solder lugs in the center connect to the positive side of the internal electrolytic capacitors. All internal capacitors share a forth common solder lugs at the rim for their negative connection.

I use wire cutters to uncrimped the bottom of the multi-section capacitor. Then I use needle nose pliers to pull the crimped sections away from the base. This allows me to pull the guts of the multi-section capacitor out of the aluminum can.

The anatomy of a multi-section capacitor. The four internal electrolytic capacitors are rolled up into one assembly.

I was able to fit all four replacement electrolytic capacitors inside the aluminum can. A dab of hot glue holds the components in place. I use tiny brass screws I get from a local craft store as solder anchor points.

Pictured below is the refurbished multi-section capacitor installed back into the chassis.

All of the components attached to the multi-section capacitor have been soldered to its bottom terminals.

I use a Dremel with cutoff tool to remove the area from the base of the multi-section capacitor's aluminum can that I bent with needle-nose pliers.

I then use the Dremel with wire brush tool to remove burrs.

I spray the external cardboard wrapper of the multi-section capacitor's aluminum can with some flat black paint to make it look as good as new.

Hot glue holds the aluminum cover in place over the multi-section capacitor's base. You will never know it was refurbished once the aluminum cover is installed!

There is one other 100uF capacitor capacitor, circled below, that also needs to be replaced.

The top electrolytic capacitor in the picture below is the original 100uF 25Volt capacitor, the bottom one is its modern equivalent. Notice how the new modern equivalent is in a much smaller package?

Circled below is the newly installed 100uF 25Volt capacitor.

Step 5 Replacing Paper Capacitors

Paper capacitors, like the ones circled below, become very unreliable with age and should be replaced with one of similar capacitance and equal or above voltage rating. Paper capacitors are not polarized although they may have a black band on one side indicating which lead is connected to the outside foil.

I replace paper capacitors with new Polypropylene type. Circled in the picture below.

I almost forget to replace the paper capacitor that is on the top side of the chassis. This capacitor is part of the antenna circuit.

Here is a pic of the new Polypropylene capacitor soldered in place.

Step 6 Selenium Rectifier Replacement

The S-72 employs a Selenium rectifier, circled below, to convert household AC (Alternating current) current to DC (Direct current) required by the receiver. As Selenium rectifiers age, their forward resistance increases to the point where it causes the power supply voltage to drop. Initial testing while powered by household current showed that the B Voltage, measured at capacitor C38c, was below the specified 90 Volts DC.

Below is a comparison in size of a Selenium rectifier compared to its modern replacement, a 1N4005 Silicon rectifier. The 1N4005 has a forward current rating of up to 1 Amp where the original Selenium rectifier only have a forward current rating up to 150 Milliamps.

When replacing the Selenium rectifier with a modern 1N4005 Silicon rectifier, I had to install a 100 Ohm tapped wire-wound resistor in series with it as a Silicon rectifier is much more efficient. I then adjusted the tap on the wire-wound resistor until I measured the desired "B" Voltage of 90 Volts DC at capacitor terminal C38c.

I was having issues with filament or "A" Voltage being below the specified 7.5 Volts DC. This voltage is measured at capacitor terminal C38a. With the power off, I performed some resistance checks and determined that part of the tapped wire-wound resistor, R29 in the schematic, had increased in resistance and was out of spec. I connected a 75 Ohm 25 Watt wire-wound resistor in parallel to decrease its equivalent resistance. The filament Voltage once again rose to the required 7.5 Volts DC.

Step 7 Marking the Hot side of the AC plug

Depending on how the non-polarized line cord plug of the S-72 is plugged into a power outlet, an high voltage potential can exist on the metal chassis. Below my Multimeter is reading 120 Volts AC between the chassis and ground, in this case ground is the metal enclosure of the household sockets. This poses a potential shock hazard!

Now, if I reverse the line cord plug, I get a very low voltage (less than one Volt) AC between the chassis and ground.

Normally, I would install a polarized plug on the end of the radio's line cord, ensuring that the chassis was at or near ground potential. I can't do that with the S-72 as you have to plug the line cord plug into the slots on the top of the chassis in order to operate on battery power.

Since I could not install a polarized plug, I marked an "H" for Hot on the side of the plug that should go into the smaller slot on the AC socket. If properly wired, the smaller slot on the household AC socket is "Hot" or 120 Volts AC with reference to ground. The larger slot on the household AC socket is "Neutral" and it should be less than 1 Volt AC with reference to ground.

Step 8 Alignment

btuIf is a perfect time to perform the alignment procedure, as the S-72 chassis is already removed from the cabinet. Alignment involves injecting a AM modulated signal, of frequency specified in the manual, then watching for maximum AC Voltage measured at the speaker terminals. This is done while tweaking variable capacitors if the input frequency is at the high end of the band or ferrite slugs in RF coils if on the low side of the band. You must perform this process for each position on the Band switch. Page 6 of the S-72 manual explains the process. There is button called "Hallicrafters S-72 Manual" in the beginning of my blog that will take you to a web page where you can obtain the manual.

Step 9 Cabinet Cleaning and Restoration

The S-72's cabinet is covered in a leatherette material with brass accents. I sprayed the exterior with Windex then wiped it down with a paper towel. I repeated this process, discarding the paper towel and getting a new one, with each cleaning cycle. The process was repeated until the paper towel showed very little evidence of dirt. Below is a picture of my paper towel on my first cleaning pass.

Meguiar's Motorcycle All Metal Polish was used to remove years of oxidation from S-72's brass plated feet.

Meguiar's Motorcycle All Metal Polish was also used to shine up the brass plated air vents in the side access door and the pull handle.

Meguiar's Chrome Polish on Amazon!

Meguiar's Metal Polish works great on the brass and chrome fixtures on vintage radios.

The air vents and pull handle on the side access door cleaned up pretty good. Unfortunately, this was not the case for the brass plated hinges, they were badly rusted with most of the brass plating gone.

I decided it was best to paint the hinges on the side access door. First, I applied masking tape around the hinges to ensure that I would not mar the leatherette exterior. I then used my Dremel with wire brush attachment to remove as much rust and corrosion as possible in order to prep for paint.

I wiped down the hinges with Prep-All, a degreaser and de-waxer used for automotive paint prep. I then masked off the side access door, so that only the hinges were exposed. The hinges were treated with a coat of brass colored Acrylic Enamel spray paint.

The hinges turned out really great! The brass colored Acrylic Enamel spray paint adhered really well to the old hinges.

I also wire brushed the heads of the screws that attach the side access door to the cabinet, degreased with Prep-All, then treated them to a coat of brass colored Acrylic Enamel spray paint.

The leatherette material that covers the cabinet was coming off in places. I used Elmer's School Glue to adhere it back to the cabinet.

I cleaned the inside of the cabinet with a lemon-oil based furniture polish.

I sprayed then wiped down the outside of the cabinet with an "Armor All" like protectant that I purchased from a local auto parts store.

The lid was also sprayed and wiped down with an "Armor All" like protectant.

Step 10 Front Panel Replacement

The front panel was missing from my S-72, I believe a previous owner was using this as a "parts" radio.

Luckily, I have a father-in-law with a CNC router setup in his garage. He was more than happy to fabricate a new front panel for me. First, I needed to plot out the dimensions for the panel to give him. I put my drafting skills to work.

Next, I created a paper template from my dimensions to double-check for fit.

I then scanned to PDF my front panel drawing with dimensions then e-mailed it to my father-in-law who lives on the California. A few weeks later I received the finish faceplate in the mail. It was beautiful! My father-in-law machined it out of a composite material that consist of a layer of plastic sandwiched between to sheets of thin aluminum. I checked the new faceplate for fit, by temporarily installing the chassis into the cabinet and installing the knobs.

The new front panel fit perfectly. I decided it was a good idea to install the dial lens and to glue the new speaker grill cloth in place before installing the front panel.

The front panel is going to be glued to the top of the S-72 cabinet. I am going to use large fender washers secured with screws and bolts to hold the face plate in position while the glue dries. I put electrical tape on the side of the fender washer that is to comes in contact with the front panel so that is does not mar the surface.

I put a bead of E6000 adhesive on the back of the front panel.

Once the front panel was aligned properly on the cabinet, I used the fender washers with nuts and bolts to secure it in place while the adhesive dries. I used the phone jack to secure the upper right-hand corner.

Here's how the front panel looks once the fender washers, nuts, and bolts have been removed. Notice that the holes in the front panel are slightly out of alignment with cabinet holes. The knobs will conceal this alignment problem.

E6000 Adhesive on Amazon

This is my main go-to adhesive for use around the shop. This adhesive is strong, flexible, dries clear, and works great for bonding wood, metal, fiberglass, and ceramics.

Step 11 Assembly

The original antenna mounting bracket was missing from my S-72. I fabricated a new one from an aluminum heat sink I had in my junk drawer. This heat sink already had a solder lug attached to it which made it easy work to solder it to the external antenna connection on the chassis.

In order to make handling the chassis easier, I removed the phone jack. Now, I had to connect it back in before the chassis was inserted into the cabinet.

The chassis slips in through the side panel and is held in place by two bolts built into the inside of the cabinet. I had to supply my own lock washers and nuts as the originals were missing.

I found a suitable replacement telescopic whip antenna on Amazon. My fabricated antenna bracket is held on the side of the cabinet with tiny brass screws I purchased from a local crafts store.

When mounting the knobs, I place a slim piece of cardboard underneath them while tightening the set screw so that each knob is a uniform distance from the front panel.

Time to attach the side panel. It is held in place with four screws. These screws are the ones I painted earlier in my blog.

With the side panel in place you must solder the two connections between the chassis and the built-in loop antenna (circled below).

I built a battery box that contains 9 Volt batteries connected in series to supply the required 90 Volts DC and 1.5 Volt D Cell batteries connected in series to provide the required 7.5 Volts DC. A tube socket is mounted to the side of the battery box. The battery connection from the chassis plugs into the tube socket. I have a separate blog that covers the battery box construction.

You must plug the line cord into the chassis in order to operate from battery power.

Hallicrafters provided these handy leather straps in order to tame the line cord.

Here is a picture of my S-71 with custom battery box installed.

A final test is to see if the side door closes properly with the custom battery box installed. Looks like it is a perfect fit as the side door closed and latched propertly.

Finally, here is a picture of the finished product!

Video of my newly rebuilt Hallicrafters S-72 in action!

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