Driver tube bias?

[jlschweiger]

Still wet behind the ears here, should I be checking the driver tube bias every so often as a "check up" or does this only need to be done if the driver tubes are replaced?  Really enjoying the Paramounts...
Thanks for any replies!

[Doc B.]

No checkup necessary. The only indicator of needing a new tube is if the one in the amp sounds like it is worn out, i.e. the overall sound is getting flat. Even if a tube is getting long in the tooth sonically it won't hurt anything.

[jlschweiger]

I'm considering trying some tube rolling with some WE396A's as the driver tubes.
Would I need to check/adjust the bias if I substitute these for the original driver tubes?
Thanks!

[Paul Joppa]

Yes, the bias should be adjusted when a new tube is substituted. I would check it again after about 100 hours - it probably won't have drifted, but if it does, adjust and check in another 100 hours. After it's stable, most tubes will go for years with very little drift. But each tube is different - even the same brand, date, and type - so re-check when you change tubes.

I think you want to be within 5% if you are set up for 2A3s; the 300B with cap coupling can be off by 10% with little audible effect.

[jlschweiger]

Mr. Joppa,
Thank you for your reply, Sir!