Power tube matching...??

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by tedjac, Feb 1, 2006.

  1. tedjac

    tedjac Guest

    How important is it that power tubes "match" each other? What happens if they don't match... can you actually hear the result? Can the bias adjustments be made to compensate for tubes that aren't matched? Is it more important in a four tube set up (4 6V6s)? What percentage tolerance is considered "matched?"

    Thanks
     
  2. amper

    amper Member

    Messages:
    550
    Joined:
    Jan 3, 2005
    Location:
    US
    Depends on the amp.

    Some amps can bias tubes separately, some can't. None of mine can, they're all fixed, non-adjustable bias.

    There are several schools of thought on the importance of matching tubes, the which I do not have enough time to get in to. The big thing with Class AB amps is to try an eliminate crossover distortion, which is generally a bad thing.

    I would recommend you read the information from the tube and amp dealers on the subject, like Mesa/Boogie, Groove Tubes, KCA, Lord Valve, Randall Aiken, Myles Rose, etc, etc, to gain an understanding of some of the different viewpoints
     
  3. donnyjaguar

    donnyjaguar Member

    Messages:
    4,243
    Joined:
    Nov 4, 2005
    Location:
    Canada
    The short answer is, the closer the tubes are matched, the more efficient your amplifier will run.

    Whether this is a good thing will depend upon who you ask. :)

    DJ
     
  4. tedjac

    tedjac Guest

    So, with four power tubes (as in my Fuchs ODS30SLX), it would seem to be even more important... good to know.
     
  5. trisonic

    trisonic Member

    Messages:
    13,164
    Joined:
    Mar 24, 2003
    Location:
    NJ out of England
    Interestingly you can bias each tube on Maven Peals individually - you do not need matched pairs as most other amps.

    Trust this helps.

    Best, Pete.
     
  6. donnyjaguar

    donnyjaguar Member

    Messages:
    4,243
    Joined:
    Nov 4, 2005
    Location:
    Canada
    After putting in separate bias adjustments for each output tube I guess to really do the job properly you'd need some means of balancing the output from the phase invertor to compensate for the difference in transconductance of each tube. I'm envisioning a 500k pot with the wiper to ground in place of the bias-to-ground resistors. To get this contrivance operating properly would also call for removal of the negative feedback circuit and use of an oscilloscope. This is starting to sound like more work than just using a pair of matched tubes.

    DJ
     

Share This Page