Random Bias Drift - Need Expert Advice

[SonicExplorer]

Hello,

 

Is it possibly normal for an amp to have a random bias drift of 6ma or so?

 

I just put in a new set of matched EL34 tubes and the bias measures differently depending on the time of day I measure it. I've checked all tubes and the drift follows all the tubes equally. I also swapped the phase inverter tube, no change. I also tried two different meters. Also checked the AC feeding the amp - and its always within a 5v range (122v-127v).

 

Anyone have a clue what may be going on here?

 

Thanks,

 

Sonic

[Duesentrieb]

Those 6mA drift - how much percent is that? >10% ?

I'm asking for two reasons:

a) your prim. has a drift of 4%, which will cause the sec. to drift 4% too, which will cause the bias to drift.

b) new tubes need time to burn in. Play the amp at good volume for 2-3 hours and check again.

[Dropsix]

It's gremlins, tiny little gremlins having sex orgies in your map.

 

Every time a guy gremlin splooges he shorts something out and it's {censored}in your {censored} up.

 

Call for gizmo, NAO.

[SonicExplorer]

 

Those 6mA drift - how much percent is that? >10% ? I'm asking for two reasons: a) your prim. has a drift of 4%, which will cause the sec. to drift 4% too, which will cause the bias to drift. b) new tubes need time to burn in. Play the amp at good volume for 2-3 hours and check again.

 

 

6ma would be 20%, or 10% in either direction of a "center" (although I honestly can't determine what exactly the "center" is technically).

 

The tubes were burned in prior to purchase on a burn-in machine. My understanding is that if it were normal drift due to lack of burn in, it would generally drift in one direction and never backtrack, but that's not what I'm seeing. Furthermore, normal drift due to lack of burn-in would not cause ALL the tubes to follow in common. In my case, the tubes have been burned in and matched, and they are staying matched in terms of the bias reading regardless of the direction or magnitude of the drift . This doesn't apper on the surface to be an issue with the tubes but I cannot figure out what else would be causing this, or if this is normal side-effect of something else (doubtful).