I have a tube radio that sound great, but after a few minutes when it heats up the speaker sounds distorted.
All the caps were replaced.
I checked all the tubes. there OK. I was thinking of replacing all the resistors.

Do you have any ideas?

Wholesale replacement of resistors is probably overkill. It could be a tube or something else that begins to fail when it gets warm. Can you provide the make and model?

:I have a tube radio that sound great, but after a few minutes when it heats up the speaker sounds distorted.
:All the caps were replaced.
:I checked all the tubes. there OK. I was thinking of replacing all the resistors.
:
:Do you have any ideas?

:Wholesale replacement of resistors is probably overkill. It could be a tube or something else that begins to fail when it gets warm. Can you provide the make and model?
:
::I have a tube radio that sound great, but after a few minutes when it heats up the speaker sounds distorted.
::All the caps were replaced.
::I checked all the tubes. there OK. I was thinking of replacing all the resistors.
::
::Do you have any ideas?

I'd measure all resistors (in circuit ) first..if any are out of 10% tolerance, lift one end and measure again (out of circuit). If still out of 10% spec..replace them. Once that is done a can of freeze spray may help to isolate the problem once the set begins to distort.
Joe

Does the volume also decrease? If so; I would suspect a gassy tube, likely the audio output or 1st audio. You can monitor the control grid of the tube with a meter (needs to be a high input impedance type like most modern digitals) and watch to see if the voltage gradually changes as it warms up. Once it distorts, take something like a 1 meg reistor, clip one end to ground then momentarily touch the grid with the other end, If it clears up the sound, make sure there are no increased value resistors in the grid circuit. Assuming all the caps have been changed; then replace the tube. It's probably gassy. This causes an excessive negative charge to gradually develope on the grid after a time choking off the tube. On the other hand if volume stays good but is distorted, look for increased resistor values that supply negative grid bias to the audio output tube(s). You can also monitor those grids to check for abnormal voltages.

::Wholesale replacement of resistors is probably overkill. It could be a tube or something else that begins to fail when it gets warm. Can you provide the make and model?
::
:::I have a tube radio that sound great, but after a few minutes when it heats up the speaker sounds distorted.
:::All the caps were replaced.
:::I checked all the tubes. there OK. I was thinking of replacing all the resistors.
:::
:::Do you have any ideas?
:
:I'd measure all resistors (in circuit ) first..if any are out of 10% tolerance, lift one end and measure again (out of circuit). If still out of 10% spec..replace them. Once that is done a can of freeze spray may help to isolate the problem once the set begins to distort.
:Joe

:I have a tube radio that sound great, but after a few minutes when it heats up the speaker sounds distorted.
:All the caps were replaced.
:I checked all the tubes. there OK. I was thinking of replacing all the resistors.
:
:Do you have any ideas?
Hi Lawrence, it sounds like you have a leaky cap on or around your output tube , but you say all caps replaced? what is radio and model maybe if we take a gander at the schematic we might find a cause.
E.

Hi,
I just has a small AA5 that was giving me fits like that. Worked fine, then after about 3 or 4 minutes the sound would distort.
It turned out to be the 50C5 tube. No real reason, it "tested' fine on the tester, but under actual conditions it failed.
Before replacing all the resistors, look for something more obvious. You can save a lot of time in case it isn't the resistors.
Good Luck!
Gary.

::I have a tube radio that sound great, but after a few minutes when it heats up the speaker sounds distorted.

Robert had the right idea.

As far as 50C5 tubes are concerned, though, I've had this problem with a few, too. Could be that your tube is gassy, or the elements could be shorting after the tube gets really hot. They are closely spaced. A slightly gassy tube will often test normal. You need a gas indicator light on your tester in order to find gas.

T.