Bias balance pot?

[Blair]

I finally got this fella wired up with the ST70 front end. I need to change the plate resistors to closer to 43K (using 68K now). It sounds much better and much more powerful.

The curious issue I see is in the bias. When fired up, it is fine, nothing abnormal. The issue is that the tubes take forever to settle down.

Example: tube 1 may be at 45mA while tube 2 is at 57mA. Walk away for 5-10minutes, and they are almost perfectly biased again.

Any ideas?

I like these 7591 tubes. Really nice!

I will post an image soon of the finished amp.

Thanks!

Blair

[battradio]

7591's are very picky , the gird resistor has to be 220 k ohms or less the will bias drift

[Blair]

OK. I will take a look. Bette question is whether it is bad to leave it alone?

Thanks!

Blair