I recently purchased an old Bakelite tube radio, an Admiral Model 5R11-N. It works very well except for a slight hum, not too bad but more than I think should be there. OK, the speaker cone has a small tear in it but that has no audible effect until the volume gets pretty loud and by then the hum is pretty annoying anyway!
I have tested all the tubes and they all test as very good. Some of the resistors are off by more than 10% (the worst one is about 15% off nominal value). So I think the hum is coming from the caps.
I would like to replace the caps but the surfaces on a couple of them are so bubbled that any markings have long ago disappeared. Can anyone recommend a way to determine the proper cap values?
I have tried to find a schematic for the radio online but so far, no luck. (It does have the tube layout sticker on the bottom though!)
I have tested all the tubes and they all test as very good. Some of the resistors are off by more than 10% (the worst one is about 15% off nominal value). So I think the hum is coming from the caps.
I would like to replace the caps but the surfaces on a couple of them are so bubbled that any markings have long ago disappeared. Can anyone recommend a way to determine the proper cap values?
I have tried to find a schematic for the radio online but so far, no luck. (It does have the tube layout sticker on the bottom though!)
The most likely culprets are the electrolytic caps. In table radios, the values are fairly common. About 30 ufd for the first section and about 50 ufd for the second section. They should be rated at 160 to 200 volts.
Coupling caps, except for those in the RF section, are not too critical. They should be rated at 200 volts or higher. You might use a lighter or a match and try to melt the bubbled wax on the old caps so that you'll be able to see the ratings.
Happy re-capping.
Coupling caps, except for those in the RF section, are not too critical. They should be rated at 200 volts or higher. You might use a lighter or a match and try to melt the bubbled wax on the old caps so that you'll be able to see the ratings.
Happy re-capping.
Geek said:
Wow! what a great site! My search was obviously too limited. I didn't find an exact match for this radio but I did find one for another radio I'll work on when this one is complete!
Awesome! Thanks!
Frank Berry said:
I was hoping they would be at least somewhat standard! I don't have any experience with these table radios but have picked up a few in the past year. The first was a piece of cake to repair as everything was readable and a schematic was glued inside the back cover!
I wouldn't have thought of melting the wax. Good tip.
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