The Stovebolt Site Forums The Shop Area The Electrical Bay The Radio Bench 1954 radio BUZZZZZZ noise

I obtained a factory 1954 pickup radio at a local auction (and a heater box) for a mere $30. Not knowing the problems I could cause (it's just a radio, right?....um...a very rare radio I discovered), I made a 5.8 volt power supply from a PC power source and connected the radio up. It worked!!! It tuned in the locals and sounded like it should. Good, so far. Wanting to display my find, I mounted it in the truck, disconnected. I spent the winter researching for a voltage reducer (truck is 12 volt). Finally found one from a guy that makes them & sells on ebay. Yesterday, I pulled the radio out and did a pre-check on the bench with the reducer. And...there it was...an awful BUZZZZ...with or without speaker connected. It got loud (the buzz), but I could faintly here the local station. So I turned it off. Hooked it up to my homemade original power supply...same issue, eliminating any question with the voltage reducer.

Spent the evening researching and I think the filter cap(s) (electrolytic was the word I discovered) is bad. Per the chevy radio manual, number 19 (A & B) should be the filter caps. They are P/N 7240612 rated at 20 Mfd, 400 Volt. I think I found number 19 (12 & 17 too just for verification) on my radio. But my 19 shows P/N 1208600 with .01 Mfd, 600 volt. My number 12 has a different P/N 7236841 than shown on the manual, but is rated at the same .05/400, so I think that's ok. But my 17 has P/N 7236841 (same as my 12). The Mfd for my 17 is nowhere near 17 described in the manual.

So, finally to my questions and thoughts:

I read the filter caps can go bad when left alone in the rig over a cold winter (which we had). Would that explain the buzz compared to the previous working condition?

Next, did I locate 19 (and 12 & 17) properly on my radio? I have a pdf pic I can send someone, I can't figure out how to add it to this, sorry.

And, if I located them correctly on my radio, why the different values for 17 & 19? And how did the dang radio work last summer given the vastly different ratings?

And, it looks like two filter caps exist, per the manual, as 19A and B. This really messed me up. Where are A & B?

So finally, again if I located the filter cap correctly (19), should I install the factory rated 20/400 or the put a new one same as the old one (.01/600)?

Sorry for the lengthy post, but I'm not an electrical guy, and certainly not a tube guy!! Any help is appreciated. I can email my pics.

There are two large filter capacitors located in a metal can, I think next to the audio transformer. They will be labeled A and B on the diagram. They are both 20 Mfd. To replace them I disconnect the leads to the can underneath, install a small terminal strip and mount the two new capacitors on the strip.

It is interesting that there is buzzing with no speaker connected. If that is the case it may be that the vibrator is in distress. To see if the problem is caused by a short somewhere, remove the 0Z4 tube which is the rectifier and see if the buzzing stops. If the buzzing continues the vibrator is bad.

The filter capacitors can fail at any time when they are old. So it would be a good idea to replace them regardless.

i'm on it, thx