Test-driving preamp tubes--do I have to bias?

[cranqued]

I'm looking to take out the 12ax7 preamp tubes in a Valvetech VAC and replace them (just for a test drive) with the 12ax7's I have in my Bogner Metropolis. Any risk in doing that without biasing? I only need to do it for a short while, to rule out preamp tubes as the source of a tone issue.

The Valvetech tubes are Fender and Ei. The Bogner has Chinese tubes.

[VacuumVoodoo]

Tubes in preamps are used in a selfbiasing circuit configuration, you don't need to adjust anything. Just do it.

[cranqued]

Thanks, VacuumVoodoo! :BEER

[tralfax19645]

Hi,
I always put in V1, JJ 12AX7 V2, EI 12AX7 V3, JJ 12AT7 V4, EI 12AX7 It definately did not come stock with a fender tube.
Rob

[cranqued]

Hmm, there was a Fender 12AX7 in the last slot when I got the amp. The other JJ made it here.

By the way, Rob, I'll email you later today about the reverb tank I need to get from you.