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Biasing power amp - compubias

Posted by Heifetz on June 26, 2017 at 23:18:08:
Hello,
I checked the biasing on my power amplifier two nights ago using compubias. The amp has 4 EL34's and are recommended to be biased at 12W -18W which is 50%-70%.
Left tubes where at 13w and 14w and the right tubes 12w and 13.5w.
I decided to adjust them to 14.7w per tube which I managed to do. I noticed an improvement.
Last night I checked the bias again and whilst the left tubes seem to be quite steady at 14.5w the right tubes are reading at 13w and 13.5w.
My question:
Can anyone help me by explaining why the reading is now different. Should I try re-biasing the right tubes again? Why are there fluctuations?
Thx so much, Bob