Tubes Asylum

Newbie question: How often does the bias need to be set/checked on a tube amp?

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psgary

I don't have much experience with tube amps and just wanted to get an idea about how much fussing needs to be done with tubes. Can a tube amp basically be set up, biased, and then forgotten? Or does it require frequent checks of the bias?
I did a search and didn't find an answer to this.
Thanks for any information.

Edits: 08/19/14

Follow Ups:

RE: Newbie question: How often does the bias need to be set/checked on a tube amp? - Caucasian Blackplate 12:38:25 08/23/14 (0)
Some amps require no biasing. That might be a nice place to start.
If you buy a lowish power cathode bias PP amp you'll never need to. - Timbo in Oz 19:04:13 08/19/14 (0)
:-)!

Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger
RE: Newbie question: How often does the bias need to be set/checked on a tube amp? - Jim McShane 11:38:28 08/19/14 (4)
If the amp (or power tubes) is/are brand new check it fairly frequently - after 5-10 hours, and again after 25 and 100 hours of use. If your amp uses a tube rectifier check the bias whenever you change rectifiers - as well as whenever you change power tubes.
For an amp or tubes that are not new I check it every 3-6 months, depending on use. Some amps are more stable than others, so once you get to know yours you can make a judgement call. That holds true for a new amp or tube set too, after there's some use on it/them they don't need as frequent checking/adjusting.
There is no exact specifications on how often to check, but what I described above works well for me.
There are some biasing tips in the FAQ, check out the link below.
Edited to clarify...
- http://www.audioasylum.com/audio/tubes/messages/25/253369.ht (Open in New Window)
Edits: 08/19/14 08/19/14
- RE: Newbie question: How often does the bias need to be set/checked on a tube amp? - tube Tom 14:20:32 08/20/14 (1)
  Hi Jim, you may have noted the post below that I'm getting (gotten) my first set of manual bias amps? I pretty much figured changing power tubes would require re-biasing, but what about rectifiers? I plan to use the power tubes that came with the amp, but change the rectifiers to something better (NOS!) Will I have to re-bias when I change the rectifiers? Thank you! Tom
  - RE: Newbie question: How often does the bias need to be set/checked on a tube amp? - Jim McShane 14:25:06 08/20/14 (0)
    Yes! By all means re-bias after a rectifier change. The voltage output from the rectifier varies some from tube to tube (even if they are the same brand and number) - which in turn changes the bias on the power tubes.
    
    Please check out the link in my first post, it's full of info you can use.
- RE: Newbie question: How often does the bias need to be set/checked on a tube amp? - ahendler 16:50:58 08/19/14 (1)
  Once an amp is broken in Jim's suggestion of 3 to 6 months is right on. Don't let checking bias become an obsession. I also would check bias if you hear a change in sound of your system. Enjoy
  Alan
  - Except when - Frihed89 03:37:18 08/20/14 (0)
    You have an amp that has an unstable bias, in which case you can have it fixed, or as i do with a garage-made amp that I love, but have already sunk more time and money than it cost (not much) into repairing this and other parts of it, hook a DVM up to it and check it regularly.
    
    Hopefully, this is not the case with 90% of the fixed bias gear we buy. On the one other custom amp i have with fixed bias and other two i have sold, Jim's suggestions are 100% on...in my experience...unless you buy JJ power tubes.
    
    Observe, before you think. Think before you open your yap. Act on the basis of experience.

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