How To Restore An Arvin 33R78 Vintage Stereo Radio

The Story

As a teenager, I had a paper route. At the end of my paper route lived an elderly brother and sister who moved in together after there spouses had passed away. I mowed their lawn and did odd jobs for them. Even in my college years I would help them if they called. From time to time Joe, the elderly brother, would give things to me as a thank you for helping him and his sister out. Knowing that I was interested in electronics, he would often give me old radios or appliances to tinker with. One day, after helping Joe clean out his garage, he gave me this Arvin 33R78 Stereo that was under a moving blanket in a corner of the garage. With glee, I strapped this stereo radio to the rack over the rear wheel of my bike and carefully rode home. The radio has been in my possession for about 30 years!

---

My Arvin 33R78 Stereo Radio before the restore

​A Brief History of Arvin Industries

Arvin Industries started out as the Indianapolis Air Pump company in 1919, their first product was a reliable air pump used to inflate automotive tires.


In 1927, they changed their name to Noblitt-Sparks Industries and sold "Arvin Heaters" which were specialized heaters used in the automotive field. Back in the day most cars were not equipped with heaters. By the 1930s, Noblitt-Sparks had diversified into making radios for the automobile industry. In addition, they made Silvertone branded radios for Sears.


In 1950, Noblitt-Sparks changed their name to Arvin Industries. While still a leading automotive supplier, they branched out into consumer electronics and appliances. My Arvin 33R78 Stereo Radio was built in 1963.

​
Arvin Industries left the consumer electronics and appliance market in the early 1970s but still has as a reputation for building quality products in Automotive and Research & Development fields.

​The Problem

My Arvin 33R78 worked perfectly back in 1985. But slowly over time it developed an annoying AC hum as the electrolyte in the power supply capacitors dried up. Recently the FM Mono and Stereo modes of the radio ceased to work altogether which made me think it was time to do a full restoration on this marvelous old radio.

****Caution Electrical Hazard****

The Arvin 33R78 Stereo Radio does not employ a transformer to isolate the AC line current from the chassis. AC Power directly out of the wall is rectified/filtered and used for the B+ Voltage for the vacuum tubes. Tube filaments are configured in series so as to drop the line voltage to the proper voltage levels for the vacuum tubes.
Transformerless designs, as used in the Arvin 33R78, had a metal chassis connected to one side of the power line. While the user is perfectly safe from electrical shock due to the insulated cabinet and knobs, you need to take extra precautions when servicing the radio when removed from the cabinet.

​Chassis Removal

FIRST UNPLUG THE ARVIN RADIO FROM THE AC OUTLET! Speakers are removable and come with long speaker cords. Unwind the speaker cords and unplug from the Arvin Stereo.

Remove left and right speakers from the wooden cabinet and set aside. Also remove the knobs from the front of the Arvin Stereo.

Remove the four screws that hold the back cover onto the wooden cabinet.

Notice that the internal speaker wires are soldered to jacks on the back cover and that the electrical cord is disconnected when the back cover is removed.

You have to remove several screws from the bottom of the cabinet in order to remove the chassis.

Two nuts on the left side hold the chassis to the front of the cabinet, the second one is directly below the one circled in the picture.

Two nuts on the right side hold the chassis to the front of the cabinet, the second one is directly below the one circled in the picture.

I recommend unsoldering the internal speaker wires from the back cover then insulating the exposed ends with electrical tape or wire nuts. It is easier to work on the chassis with the back cover out of the picture.

Make sure you unsoldering the second pair of internal speaker wires and insulate the ends as well. The yellow speaker wire just came off without unsoldering. Possibly a cold solder joint.

Finally the chassis is free and clear of the wooden cabinet.

Cleaning and Lubrication

Notice the poor repair job someone did when replacing an electrolytic capacitor.

Here is the chassis and printed circuit board fresh out of the wooden cabinet. Notice how dusty and dirty.

Here is the chassis and printed circuit board after I cleaned it with compressed air. Much better looking!

I used contact cleaner to clean the contacts in the variable resistors. There is a small opening next to the terminals of the variable resistors that you can spray contact cleaner into.

I use Labelle 109 model train oil to lubricate the shafts of all variable resistors.

Make sure you lubricate the pulleys for the dial indicators!

​Test 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 too much troubleshooting. In the case of my Ardin Stereo, the filament of vacuum tube V9 (50HK6) burned out. This caused the right channel speaker audio not to work. In addition, FM Mono and FM Stereo modes would not work because the filament of vacuum tube V1 (17C9), which is part of the FM Tuner circuit, is in series with the the filament of vacuum tube V9. Right channel audio and FM Mono and Stereo modes worked again once vacuum tube V9 was replaced!

My trusty Eico Model 635 Vacuum Tube Tester in action!

​Electrolytic Capacitor Replacement

C2A (80uF), C2B (30uF) and C2C (40uF) are all housed in the metal cylinder circled in the picture.

You must jumper together where the grounding tabs of C2 where connected to the printed circuit board. C2C was replaced with a discrete 47uF 25Volt Capacitor as seen in the picture. Make sure you get the polarity correct!

C2A was replaced with a discrete 100uF 150Volt Capacitor, C2B was replaced with a 47uF 150Volt Capacitor. Once again, make sure the capacitors are polarized correctly.

C1 (120uF) was replaced with 220uF 150Volt Capacitor. Get the polarity right!

Don't forget to replace C3, a tiny 4uF capacitor towards the front left of the printed circuit board. I replaced this capacitor with a 4.7uF 50Volt capacitor.

​Testing and Troubleshooting

As mentioned, the chassis of the Arvin 33R78 is "hot", meaning it is connected directly to the AC Line. Care must be taken when testing and troubleshooting. When working on a electronic equipment with a hot chassis, I always wear rubber soled shoes and use the old tried and true practice of sticking one hand in my pocket and using the other hand to manipulate test leads and switches. I also recommend attaching the insulated knobs to the shafts of the front controls. Disconnect the power before making any changes to the chassis or the printed circuit board!As you can see from the picture, I used test leads to connect the cabinet speakers to the audio transformers mounted on the chassis.

Get the Arvin 33R78 Stereo Radio Schematic

Arvin 33R78 Stereo Radio SchematicThe Arvin 33R78 Stereo Radio Schematic with parts listings and troubleshooting documentation is available from SAMs Photofact for around $20.

The Arvin 33R78 Chassis ready for testing and troubleshooting.

​Testing the Arvin 33R78 Chassis

​Cleaning up the wooden cabinent

Arvin 33R78 cabinet before cleaning and polishing.

Look how nice the cabinet looks after several applications of Old English Lemon Oil.

I even treated the inside of the cabinet to the a good cleaning and some Old English!

​Cleaning the Knobs

Here are the knobs before cleaning.

An old toothbrush is the best tool to clean between the ridges of the knobs. It also prevents the knobs from getting tooth decay!

Here is a picture of the freshly cleaned knobs.

​Chassis Insertion

Installing the chassis back into the cabinet is just the opposite of removal.

Make sure you properly fasten the chassis into the cabinet. If a fastener or screw is missing get a replacement from your junk box or local hardware store.

You may need to use a Dremel to cut the shaft lengths of replacement screws.

Make sure you solder the left and right channel speaker connections back to the terminals on the back cover.

The back cover back in place and the speaker wires neatly wound around their caddy.

​My restored Arvin 33R78 Stereo Radio in Action!

Conclusion

The restoration of this vintage Arvin 33R78 Stereo radio was most gratifying. It took my mind off of the stresses of my daily job and reminded me of a simpler time when people had the time to sit around and listen to the radio for enjoyment.

​Radio Restoration Books On Amazon

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