Building a Doerle "Signal Gripper" Regenerative Shortwave Receiver

​My Inspiration

​I came across this great book from 1938 on how to build four different short wave receivers. What was even cooler is that someone took the time to format it in Kindle EBook format! One click and a Kindle version of the vintage "HOW TO BUILD 4 DOERLE SHORT WAVE SETS" book was mine!

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"HOW TO BUILD 4 DOERLE SHORT WAVE SETS" Kindle book on Amazon!

What is a Doerle Short Wave Set?

Doerle "sets" were a popular home built regenerative shortwave receivers of the 1930s. Designed by amateur radio enthusiast Walter C. Doerle of Oakland, California. Doerle's regenerative radio designs were published in many amateur radio magazines in the 1930s. Doerle's Short Wave Set designs were so popular in the 1930s because of the ease of construction and use of inexpensive parts in their design.

Not much is know about Walter C. Doerle or if he was even compensated for the designs featured in the book "How to build 4 Doerle Short Wave Sets" and other vintage publications.

The Doerle name lives on as his shortwave set designs are still popular with "Glowbug", amateur radio enthusiasts that enjoy building simple tube radios,  of today.

Can I still purchase vacuum tubes?

Absolutely, there are many vendors that sell vacuum tubes and high voltage electronic components required for vacuum tube circuits. Many musicians and audiophiles even today love the sound of vacuum tube audio amplifiers as they believe they produce a warmer more natural sound. As such, there are many vendors that cater to their vacuum tube needs.

The type 30 and 32 vacuum tubes, and other components used in this shortwave receiver, are available from the two vendors below.
​

​Source of Vacuum Tubes and related components

Antique Electronic Supply

Tube Depot

Building a Doerle "Signal Gripper" Regenerative Shortwave Receiver

Step 1 Source Vacuum Tubes and Electronic Parts

I found everything required to build my Two Tube Doerle Shortwave Radio set from Antique Electronic Supply (AES), the link to this company's web site was provided earlier. ​

My Eico 635 Tube Tester doesn't have the ability to test vintage Type 30 and Type 32 vacuum tubes. So I test them by placing them in an actual circuit. Pictured below is an earlier one tube regenerative receiver I built with Type 30 vacuum tube, to be tested, installed.

​Step 2 Design and Build Cabinent

The cabinet is made of salvaged wood from shelves that used to hang in my garage. I used degreaser to remove motor oil from the surface. Once degreased and dry, I used a palm sander to smooth out dents and imperfections.

​The cabinet for my shortwave receiver is going to be open type. Basically, L shaped with the top piece used as the front panel with all of the controls, and a bottom where the majority of parts are to be installed.

The shafts for the Tuning, Detector, Regeneration, and Filament controls are not long enough to protrude through the front of the 3/4 inch wood. So I decided to carve out cylindrical areas in the wood so that the shafts could protrude through the front. The first step was to mark placement. 

​Next, it was time to layout the parts on the bottom panel then check for fit and placement. I place paper under the parts and mark placement on the paper once I am satisfied with the layout.

Once I am satisfied with parts placement on the bottom panel. I transfer the drill hole positions from the paper layout to the wooden panel using a punch. 

I then use a drill press to machine the bottom panel. The holes for the standoffs are drilled completely through the bottom panel. I set the drill press stop for all of the rest of the holes so that they are drilled to a uniform depth.

I use a Wooden Hole Saw Set to drill concentric holes 5/8 inch deep into the back of the front panel.

I then use a screwdriver, like a wood chisel, to remove the remaining wood between the concentric circles drilled by the Wooden Hole Saws.

​This is how the back of the front panel looks after the remaining wood was removed from the indentations created. The indentations were then sanded to remove any roughness.

I created a paper template of the bottom panel for parts placement and to plan out the wiring.

Time for two coats of polyurethane!

I lightly sand each panel between coats.

 I glue aluminum foil, the same type you use to wrap food in, to the back of the front panel. Elmer's White Glue works fine. This foil will be tied to circuit ground in order to reduce the effects of hand capacitance during operation.

​Finally, some rubber feet on the back side of the bottom panel.

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

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

Step 3 Final Mounting of Electronic Parts

It is easiest to mount the variable capacitors, variable resistor, and ground wires to the front panel before attaching it to the bottom panel. 

I also mount terminals and knobs then label the front panel before attaching to the bottom panel.

​​Finally, I mount the hardware on the bottom panel and apply labels. I then attach the bottom to the front panel.

​Step 4 Wiring

Creating a wiring diagram a head of time makes wiring easier!

Here is my receiver ready for wiring.

​First, I wired all of the ground connections (Black wires).

Followed by the tube filament circuit (Red wires).

Then the 45 Volt circuit (Yellow wires).

Next the 90 Volt circuit (Purple wires)

Green wires for the antenna and tank circuit.

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Step 5 Winding the Plug-In Coils

Three windings are required for this regenerative receiver, all wound on Bakelite tube bases. The number of turns required for each coil can be found in the "HOW TO BUILD 4 DOERLE SHORT WAVE SETS" book.
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The tank circuit plug-in coil has a single winding while the regenerative/detector circuits plug-in coil has two separate windings.

We will need a total of six plug-in coils in order to cover the 15-25M, 24-45M, and 40-110M bands. Plug-in coils are plugged into tube sockets, using matching pairs, in order to change bands.

​The plug-in coil below is part of the tuned tank circuit, mounted on a four pin Bakelite tube base. I use 24 AWG enamel coated copper wire for all of the coils. Hot glue is used to secure the copper windings to the tube base.

A tiny drill is used to drill holes into the tube base so that the copper wires have entry points into the center of the tube base.

I scrap the enamel insulation from the ends of the wire using an X-Acto knife. I then solder the wires to the pins of the tube base.

Finally, I check each coil's continuity at the pins.

A label is inserted into each finished plug-in coil to indicate its reception bands. 

​Here is an example of a finished regenerative/detector circuits plug-in coil. As you can see, two windings are wound on the tube base.

Below is an inside view of a finished regenerative/detector circuit plug-in coil. You can see the wires from each winding enter the center of the tube base through tiny drilled holes. The wires then enter the pins where they are soldered in place.

Pictured below are two sets of plug-in coils, one set is for the 24-45M and the other is for the 40-110M bands. I ran out of tube bases and will have to wind the 15-25M plug-in coil set some other time.

​Step 6 Final Prep

Install the two Type 30 Triode Tubes and the Type 32 Tetrode tube into the proper sockets, plug the matching band plug-in coils into the proper sockets.

​​Step 7 Obtain Suitable Power Supply

In my "Battery Box", I use two D batteries for the 2 Volt filament voltage. I connect many 9 Volts in series to obtain the 90 and 45 Volts needed to power the receiver.

Fahnestock Clips on the back of the "Battery Box" provide access to the required Voltages.

The next step is to connect your newly constructed receiver to a suitable power supply, antenna, and ground. I use my external G5RV Amateur Radio antenna and main water pipe that comes into our house as a ground. In addition, connect high a impedance earphone to the front.

Here is a front view showing the Tuning, Detector, Filament, and Regeneration controls. In addition, connections for headphones. You can see my "Vacuum Tube Battery Box" power supply right below the receiver. 

​Step 8 Testing

I am using a crystal earphone for testing. A crystal earphone looks like an "open" to DC current. A 47K resistor needs to soldered accross the Phones terminals for the crystal earphone to work. 

Set the Tuning, Detector, Filament, and Regeneration controls to mid position. You should hear atmospheric "hiss" from the earphone, once the power supply, antenna, and ground are connected. Use the Tuning knob to select AM broadcasts. Once selected, adjust the Regeneration control counter-clockwise to the point of where you hear oscillation  or "squeal", then turn it clockwise slightly until the oscillation stops and the AM broadcast is clear. Use the Detector control to "peak" the signal.

​Turn the Regeneration control further clockwise to reduce receiver gain if the AM broadcast is overpowering the earphone. The only time you should need to adjust the Filament control is if your A+ batteries are getting weak. Adjust the control until there is 2 Volts at the filament pins of the Type 30 and Type 32 vacuum tubes.

​Troubleshooting

Here are some troubleshooting tips if your regenerative receiver is not working as expected.

No sound from earphone:

• Check wiring with power source disconnected.
• Connect power source, check Voltages at the power terminals of the receiver to make sure they are correct.
• Turn out the lights and make sure the filaments of the Type 30 and Type 32 tubes are glowing.
• If using a crystal type headset or earpiece to listen, attached a 47K 1/4 Watt resistor across the Phones leads to ensure the proper current flow.
• Make sure you have high Impedance headphones connected to your receiver. The Impedance must be at least 5K, common 8ohm headphones will not work.

AM Broadcast are weak, Regeneration control does not have any effect:

• Switch the two Type 30 Vacuum tubes, I found that one tube worked better as a RF Amplifier/Detector while the other Type 30 Vacuum tube work better as an Audio Amplifier. Remember, these vacuum tubes are over 85 years old!​

​Conclusion

This was a most gratifying project. When not in use it is proudly displayed on a shelf in my basement "Man Cave". Building a Doerle "Signal Gripper" Regenerative Shortwave Receiver is a great way to learn about electronics past.