RCA 8T

© Copyright Alexander D. Schapira, 2014, All rights reserved

Here is an account of how I restored and repaired an RCA 8T receiver that belonged to the parents of a friend.
It was on this radio that news of the start and progress of World War II was heard,
and so this radio holds a special place in their memory.

I hope this will be of some interest to other RCA afficionados.

Click on any picture for a larger view.


The 8T arrived in rough shape. There were no knobs, and all but two decals were gone. The eye tube was hanging loose in a bag, and the chassis was not bolted to the cabinet. Fortunately the tubes were still in their sockets and unbroken. Two tubes (including the 6E5 eye tube) turned out to be defective.

The volume control had been removed and was included in a bag along with the eye tube and some other small parts. The set was extremely dirty, but there was no rust. My first task was a cleanup.


The power transformer, the speaker field coil, voice coil, output transformer and the IF and RF coils checked out okay. It was worthwhile to proceed.


All of the knobs were missing, but I was able to obtain a set of original RCA knobs for this model via a contact on the Antique Radio Forum. These knobs had red nail polish painted on them, but cleaned up nicely with acetone.

As received
After cleaning

The knobs also got a set of felt washers behind them when I reinstalled the chassis in the cabinet.


The Volume Control had been previously removed and was electrically open, the shaft was seized, and the solder tabs were broken off. Having nothing to lose, I attempted a repair.

The metal back of the control was attached with a solder tab and came off easily. The works were held in place with a nut identical to a standard control mounting nut. Since the shaft had seized up, previous attempts to turn it had loosened the interior nut, and this allowed the internal parts of the control to become loose rendering the control inoperative. But disassembly was easy.

I cleaned and reassembled the control and it is fully functional.


The Tone Control is very unusual. It incorporates two switches -- one ON/OFF for the AC power (NC when not fully CCW), and another in series with the variable resistance, for a preset TONE setting (NC when fully CW). Both switches were non-functional (open) -- the set could not be powered on. Fortunately!

I injected DeOxit into the control and after repeated clicking, both switches began to conduct. After letting the DeOxit completely dry out, I tested the switches on AC using a 100 watt bulb for a load. The switches worked and the Tone Control is fully functional.

The Tuning Capacitor really needed a cleaning; removing it required removing the dial glass and pointer assembly and unsoldering three wires and a ground braid.
I disassembled, cleaned and relubricated the tuning shaft and ball bearing reduction drive, and reassembled them.

As removed
After a hot bath.

After cleaning, I replaced the rubber mounting grommets with new ones ordered from Renovated Radios.

The speaker/field-coil/transformer checked out okay electrically, but it needed a cleaning.

The wiring to the voice-coil and hum-bucking coil had been altered to include an external series switch which was mounted inside of the cabinet. I removed the switch and restored the original wiring.


The speaker cone had a couple of tears which I repaired.

The front bezel was heavily oxidized and discolored. And the plastic window was a bit yellowed.
The plastic window was riveted to the metal bezel in many places, so replacement was not an option. Plastic polish worked well on the window and the bezel cleaned up nicely.
The glass dial and black paper backing cleaned up well.
Dial glass
With black backing

The underside of the chassis had a bad case of friction-tape disease, brittle wiring, and old components.


After I rebuilt the power supply section and the 6F6 audio output section, I wanted to test them in isolation. Only the rectifier, new filter caps, field-coil/choke, 6F6 and the output transformer were live. To my surprise and disappointment I heard crackling noises and smoke and fumes emerged.

The culprit turned out to be the 6F6 wafer socket itself which was contaminated with grease and dirt and had become conductive! The conductivity among the various pins was low enough to dissipate sufficient power to heat up and arc.
6F6 Wafer socket
Wafer socket removed
Wafer socket conducting!

I replaced the socket (which required grinding out its rivets) and rewired it. All was now well with the power supply and 6F6 audio section. (I had to replace two other wafer sockets for similar reasons later.)


I cleaned up the chassis and the topside aluminum cans. The transformer top shell also got cleaned, primed and repainted.

Below chassis, I replaced all of the wax capacitors, and the old dog-bone resistors. I left the original electrolytic capacitors in place, for appearance, but disconnected electrically, replaced below the chassis with modern equivalents.

One of the wire-wound candohm resistors was open, and I left it in place, but disconnected, and replaced it with modern resistors.

The speaker/field-coil cable was frayed and had been cut into to wire up an external speaker. (Recall the wall switch inside the cabinet in series with the voice coil.) I fabricated a new cable braiding wire appropriate for the period.

I added X1/Y2 capacitors from line to chassis, and added a series 20 ohm 12 watt series line resistor to reduce the effective primary voltage from 123VAC to about 110VAC. (The measured current draw under normal listing conditions was 0.6 amps.)
Topside
Underside
With mounting brackets

Of course there were lots of little additional things which needed repair or replacing that are not pictured or described here.

Finally, I gave the set an alignment per the RCA instruction sheets.

I found that the set requires an antenna of at least a couple of feet for standard AM reception. I added an internal antenna around the inside of the back of the cabinet.

It was very satisfying bringing this set back to life and restoring a radio of sentimental value to friends. I hope you enjoyed the story. Please feel free to contact me at w2ads@arrl.net

    -Al Schapira, W2ADS


Page last modified 10/31/2014