Problem with cathode resistor

[liberty]

I have a single ended amp lo scherzo and it run good since 1998. Now there is a problem in one channel, it doesn't make sound and burn the cathode resistor. I changed the tubes and the resistor but it burnt again. I measured all parts and amp checked good. The question is, what to do?

Thanks a lot for any suggestion.

Lo scherzo

 

[amperex]

How about a poor tube socket that does not provide good contact to the tube bias pin?

 

[Tube_Dude]

Hi

Inspect if C3/4 are not leaky and if R15/16 and R9/10 are not open.

Ciao.

 

[Geek]

If the above mentioned components are good, use an AC voltmeter or (preferably) 'scope to look for a nasty HF oscillation. If that's the case, check the PSU caps.