V1 voltage variance with different tubes

[johndandry]

So i've been rolling some 12AX7 in V1 of my Rocket build. Some interesting findings.

With some Silverplate Mazdas, a Amperex BB and a couple of other 12ax7 tubes, I am getting about 77v on the plate of V1
with a Tungstram, RCA getting about 90v on the plate.

What ya think?

[martin manning]

The V1a triode is drawing current through some 250k ohms (power string and plate load). The difference you are seeing is just normal variation in current draw among tubes of the same type and/or their state of health.

[PaisleyTube]

just like powertubes; biasing is unique to every tube

[johndandry]

Cool, thanks. Just thought it was interesting.

[randalp3000]

different plate resistance?

[martin manning]

No, plate resistance is an AC property and this is just about the DC operating point.