Just finished stuffing and buttoning up a Rev E board. A transformer malfunction damaged my Rev C, so I simply rebuilt the whole amp. I installed the Zener mod, using 1N4740a 10v zeners, which are 5% tolerance.
I am running some old Amperex EL84s and am having trouble biasing two of the tubes. Can only get down to .38 and .39 volts at the test points before I run out of pot. They are well used tubes, and will be replaced with current manufacturers in the near future. The tubes still test fairly good on my calibrated military tester, so I would like to use them if possible.
Would going to 11v or 12v zeners help? I am trying to avoid removing components like pots, as the pads tend to pull. I could also move the 10 ohms up to 100 ohms if that would work. Anything to avoid pulling out the pots.
Suggestions?