Strange LA2a problem

I have a re-issue Teletronix LA2a on the bench with a problem I have not been able to figure out, maybe someone has encountered this before?
It works fine when turned on, then after some time (could be 10 seconds or 10 minutes, totally arbitrary) there is a huge & gnarly buzz on the output.
A secondary power resistor (R35) was toasted, I replaced it, the primary power resistor R29 and the power diodes. All power caps test good. All other components look good, I have changed all tubes.
When the noise happens, the power at R29 does not change but after R35 I can see a sine wave looking ripple component. I also see a small amount of input signal there all the time...
I can not find any component heating up...
Heater power is not affected

any ideas?
thanks!

Perhaps a tube socket going rouge?

Mark

I will look into that, are you thinking a burnt or corroded socket contact?
I have tried jiggling all the connections and tubes, with no effect...

Yes, that's what I'm thinking. Had a similar run away problem with an Ampeg amp that turned out to be tube sockets.

Mark

nielsk said:

I will look into that, are you thinking a burnt or corroded socket contact?
I have tried jiggling all the connections and tubes, with no effect...

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