Tube Sets & single failing tubes

Originally Posted by TryHiFi

How many folks collecting tube radios have found that a large number of old tube sets tend to fade out signals, have volume issues or similar problems?

You hear a lot about capacitor hum and that's definitely a problem but after twenty tube sets, I'd say that most of my tube sets benefit from a new primary detector/amplifier/AVC type tube. When that's changed out it seems most perform fairly good without much further tinkering.

I think non-tube folks just know the radio doesn't play or tune right and so pass them on for next to nothing even if the repair is a 6 dollar tube.

Am I alone in this "single tube replacement" phenomenon?

On another note, does anyone know of a good site which lists compatible/workable twin diode-triode to triode heptode exchanges?

Thanks for listening.

Is this akin to the "lone gunman" theory? Seriously, I have a Zenith table top radio that started to have trouble "locking into" a station. I'd tune in a station, then the sound would fade out--until I turned the tuner dial to get it back. Replacing the 12AT7 tube with a new one solved the problem. The old 12AT7 tube tested good but marginally good, so I just replaced it on a hunch. The single tube theory worked for me.

Incidentally, except for the 19T8 and now the 12AT7 tubes, all of the tubes in this are original Zenith marked tubes. I agree that tubes last longer than people give them credit for. From a vintage tube manual I've read (from the early 1960s when tubes were current technology), it was documented that many tube failures were secondary to other electronic failures or poor design of the circuit in general (such as insufficient ventilation being provided for in the chassis).