RCA - Q36
Written by Russell Sher   

Coaxing life back into an RCA receiver - From Russell Sher
 

A month or two ago a colleague of mine mentioned that he had an old radiogram which was due to be dumped since it was providing little more activity other than dust collection in a garage. Perhaps there’s something that enthusiasts have in common when it comes to having a soft spot for such items, but needless to say it found its way to my location. The chassis arrived first and then a few days later the cabinet followed after loading it up onto our boat trailer and having an understanding other half cart it home.

On the back of the chassis it was stamped ‘RC585’ and it turned out to be RCA Victor from about 1946. After a brief bit of Googling, I turned up some very useful information. Apparently the chassis is also referred to as a Q36. The difference may be due to the different options - table model or radiogram model. The information included a schematic as well as alignment instructions. It was published by John F. Rider who was the CEO of John F. Rider Publications and publisher/engineer/writer of radio/electronic textbooks.

The next step was to dust off the chassis and speakers and have a good look in and around. The chassis had several wires leading off to the dial indicator bulbs, magic eye tuning indicator and speaker sockets. The mains cable needed replacing.

Soon after this, one of our club members gave me some insight about the typical audio output stage of the time which used a PI filter type arrangement in the DC path with large chokes forming both the filtering and the speaker magnetics. This was identified on the schematic.

The electrolytic caps were replaced and the speakers connected, the unit was fired up and… nothing.

The schematic was very helpful and showed that the 95V DC was not present where it should have been. The next Saturday I spoke to another club member who had a look and also gave some good suggestions – namely about the 95 Volts is being pulled down. It was also discovered that the audio output transformer had a high dc resistance on the primary on one side of the centre tap. Again the schematic proved useful as it gave the static DC resistance that should be measured. The same club member came to the rescue as he provided me with a spare audio transformer. The elusive 95 Volts had still not appeared;

After some tracing, the area was narrowed down to an RF coupling coil and it was proved that there was a short between the primary and secondary coils. This is perhaps a less common fault, but it appeared that where the primary winding was led to the solder tags, it passed over the secondary and perhaps insulation broke down at some point due to age or overheating. I picked at a piece of the winding which flaked off, but I managed to reconnect it at another point and insulated it from its mate.

Then after reconnecting and switching on – life! CapeTalk came through on 567 KHz.

The magic eye glowed with a satisfying green and we were in business.

I had had big plans to reconstruct a new cabinet, but realism set in and I took the old cabinet and did a few changes. Spiders were evicted, the record player section was cut off, the ball and claw feet were removed and I now had a smaller cabinet which housed the radio.

All of the above is by no means true restoration; true fanatics will replace most passive components (often restuffing the original capacitor housings), sandblast the chassis and lovingly tweak and poke. In this case it is really just a repair.

At this point, a short piece of wire formed the antenna, but a brief search turned up plans for a 4 foot loop antenna. This antenna consists of a wooden cross with supports at the end of each leg to accommodate the windings. Construction was begun with sawing and drilling. Each arm is about 1.8 metres long.

With some enthusiastic help from my son Justin we wound 9 turns of wire around the ends and fitted a tuning capacitor. The loop was attached with co-ax to the radio via a separate pick-up look around the main loop.

Now reception really improved. All in all this was a very rewarding exercise. To date only one problem remains – The antenna has lice! The wood seems to have been infected (before I bought it). Oh well I suppose every system has a few bugs in it!

73-Russell-ZS1RUS

 
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