In the picture is an RCA 85TA 5-tube table radio manufactured around 1938. My grandfather bought it new and the radio sat on my grandparent's kitchen counter for as long as I can remember and then the radio eventually ended up in my hands.
The cabinet finish required a complete restore and the radio emitted a loud hum when I switched it on - loud enough that I switched it off right away. A sure sign that the electrolytics in the power supply had dried out. Fortunately the tubes all checked out OK and all the mechanical parts were fine. I obtained a schematic for the radio and set to work.
Once the chassis was opened up, inside looked more like a kind of electronic stew - a jumble of brown, waxy tubular capacitors and resistors connected point to point with every connection hand soldered. Not as neat and tidy as modern PCB construction but functional.
I replaced the wiring as the rubber insulation had badly deteriorated. I replaced all of the resistors, "paper" capacitors and the electrolytics. In addition, the power transformer showed signs of having been overheating. This would have been due to the radio being left on when the power supply electrolytic capacitors had dried enough to cause them to short. I replaced the transformer - fortunately suitable replacements are still being made for guitar amplifiers. The transformer I chose, and closest to the original specs, was the Hammond 290AX, made for a Fender guitar amp but a perfect fit.
Here is a view of the inside after restoration. The chassis was a mess (see picture below); rusted in some areas. I cleaned it up and painted it. I also added a fuse. Notice the new electrolytics. The originals were the height of the IF transformers on the left and were about 1.5" in diameter and had completely dried out and had to be replaced. I know that radio restore purists would have kept the original cans and put the electrolytics inside the chassis. However, as I had already replaced the transformer, all the the wiring, resistors an paper capacitors and grid-bias battery (see below), it made sense to me to take the approach that I did. I made some printed circuit boards to mount the electrolytics in the existing cut-outs as shown. Again, not true to its original form, but resulted in a very clean job.
The cabinet is furniture grade with beautiful matched dark walnut veneer. The four controls: power/volume, tone, band (AM/SW) and tuning have unassuming brown Bakelite knobs. The tuning dial is lit from a bulb that sits behind the dial pointer. It is clear that this radio was intended to be a really nice addition to the home. A few interesting things about this radio. The tuning dial has presets for popular radio stations. One button is labeled "KOMO" and that station is still broadcasting from Seattle WA.
The other interesting thing about the radio is that it uses a "grid bias" battery for the audio stage. The acorn sized battery had long since dried out. I replaced the battery with an adaptor I made that uses a CR1220 lithium coin cell and a voltage divider made from two 4.7M ohm resistors to get the 1.25V needed to bias the grid.
One final detail: Inside the radio cabinet is a warning that a license was required to operate the radio. The $50.00 fine would be about $750 in today's dollars. Or, the option of serving a three month prison sentence was offered!
