TAB V72a unstable amplification

[el_rhodes]

Hey guys! I'm a happy owner of a racked pair of TaB V72a.
But i'm having troubles with one. Its distorting very quickly and doesnt really reach 34db of amplification. The big problem is actually that the amplification kind of oscillates.. it slowly but constantly increases and decreases.. i already tried other tubes and it behaves exactly the same so its not the tubes... any ideas what it could be?

 

[scott2000]

Electrolytic Capacitors?

 

[Tubetec]

Check if your ht voltages are in the right ballpark . Theres a good chance some of the psu smoothing caps are out of spec at this stage, check for leaky coupling caps too .

Seeing as you have one of those modules open on the bench ,would you mind measuring the enclosure inside dimensions for me?
WxHxD in mm

 

[Michael Tibes]

Isn't there a 10 M resistor at the output tube? Checking / replacing / cleaning it might help. And I'd replace the caps anyway.

Michael

 

[CJ]

original transformers?  silk sleaving can get funky,  phantom power can zap thru insulation due to inductive kick,