Power tube bias info please

[Jarrodpimentals]

I’m just trying to learn more about these things. I have a evh el34 50w head. When I bought the amp I put in all new jj tubes (el34 and Ecc83) and biased according to Howard kaplans specs at 45mv So I recently decided to try some svetlana el34’s I put them in and check the bias before playing it and the amp was reading 105 instantly. So I biased it back down to 45. So does this mean the svetlana is a much hotter tube than the jj? Or also do you think my amp went that far out of bias in 9 months ?

 

[jeremy]

hard to tell, but different tubes have different characteristics, hence the adjustable bias. id imaging its a mix of a very different tube and maybe some drift over time

 

[JMP/HBE]

Power tube bias is set in relation to plate voltage not just some random number.
And each tube has a diffferent impedance {z}.
I had used the new Svets last 5 years but the last quad i got from the same seller of 10 years would not bias correctly.
The Svets do bias in my JCM 2K DSL 100 but not my JMP and ive never had a set of tubes not bias before.
I brought up the bias issue with the seller and tried to get a refund but he was a horses caulk about insisting he was right and i was wrong.
Happy to report we parted ways.



I broke out my quad of Blackburn Amperex XF2 EL-34's ive been saving as no time like the present.
Things in the vacuum tube world have gone strange.