Liverpool redplating

[Guus]

Hey Guys,
I have some troubles with my selfbuild liverpool
Did a burn-in test for 10 hours and no problems at all. Amp sounded very nice.
But now, a few days later when the amp is on for an hour or so it begins to redplate at the EL84.

I messured the voltage over the kathode R's and yes the current goes slowly up on the inside and on the outside tubes.

When I messured the DC voltage at the crossing of 220k and 22nF I saw the DC voltage on one side slowly raising from severeal milivolts to several volts. The other side stays on some millivolts.
The 22nF cap is checked and is not leaking.

I've tried also the following things:
- some matched tubes but the problems stay's;
- checked all grounding soldering.
- messured the resistance of the OT. One side is 74 Ohm, other side is 90 ohm.

Anyone cam figger out what is wrong.

grtz
Guss.

[Guus]

Sorry guys,

I think I've solved the problem.
I used 2 different matched pairs. (Tung-sol)

I pulled 2 of the 4 tubes (so one pair of 2 EL84) and the problem comes up after some time. So this set doesn't work.

Replaced the 2 tubes by the other that I had pulled earlyer and no problem aat all. Amp runs fine.

I added 2 new matched EL84 tubes and it seems the problem is gone.
Probably a 'runaway' EL84 tube in one matched pair.

gtz
Guss