1977 Ampeg B15n- pin 4 screen voltage is well over the stated spec

[pbman1953]

My amp seems to have lost some power and this is very recent.


It's had its caps replaced and its been fine. Last night it wasn't the same amp.


A friend told me to check the screen voltage which should be 445 but it's well over at 550


What's to check first?

[SEL49]

Replace 6L6s first.

Measure voltages on both 6L6s pins 3, 4, 5, and 8. What have you?

Is the PT original?

[pbman1953]

I've tried a few sets of tubes.

One side is 519 volts and the other is about 509-  using A Bias Rite meter


PT is original

pins-
3-548
4-542
5- -051


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