Different tube pairs?

Discussion in 'Amps [BG]' started by Al Florenzo, Dec 4, 2013.


  1. Al Florenzo

    Al Florenzo

    Joined:
    Sep 19, 2011
    So I have a Traynor YBA-200. It's got two pairs of 6550s in it. The tubes pairs inside are by different manufacturers. Is this a problem? They're all 6550s and it's been working without a hitch, but I just want to know if this could cause future problems. I don't really know how old they are, so I was thinking of getting new ones sooner or later anyways. Any advice would be appreciated. Thans! :atoz:
  2. T-Bird

    T-Bird

    Joined:
    Apr 29, 2007
    Location:
    Finland (Northern Europe)
    Hi.

    Unless You can bias the individual tubes (/pairs/banks) separately, mixing output tubes is always risky.

    IIRC, one can't on YBA.

    When the bias drifts as the tubes age, one pair can start fight against the other two and that kind of distortion can sound good to some ears.
    Not before long something lets out the magic smoke, and that's always expensive.

    I wouldn't do that.

    Regards
    Sam
  3. beans-on-toast

    beans-on-toast

    Joined:
    Aug 7, 2008
    If all the tubes are matched it isn't a problem. If a single tube goes out and you find one that matches (they would have the same transconductance and cathode current at the plate voltage that the amp operates at). Unfortunately you can't tell if they're matched unless you have a way of testing them. If they aren't matched you might hear a hum that is louder than normal. Unmatched tube can also wear down the others faster.

    If you can get access to an infrared thermometer (automotive and heating/air conditioning folks use them), you could measure the bulb temperature of the power tubes. This can give you an indication as to whether or not some tube are running hotter than the others. This can be an indication that the tubes are not well matched.
  4. InsanityAmps

    InsanityAmps Supporting Member

    Joined:
    Jul 9, 2013
    Location:
    Portland, OR
    If it's running fine now and not humming I would not worry about it unless you see a tube with its plate glowing red. It would most likely be humming at that point though. You're not going to do any damage to your amp having non perfectly matched pairs. Worst case scenario is you lose a tube at some point then it's time for a new set.
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  6. Mosfed

    Mosfed The mighty mighty Supporting Member

    Joined:
    Apr 21, 2013
    Location:
    On the Mont Blanc
    Its clearly not ideal. Especially if you have no way of checking how closely matched they are. But if you can bias them and get them close, it's probably not fatal or anything. The most likely outcome is that you will go through tubes faster. It is possible it could create bigger issues though if you have a serious tube failure.
  7. teemuk

    teemuk

    Joined:
    Mar 1, 2011
    Which version is it?

    First one had an automatic biasing feature. The second one didn't.
  8. Mr. Foxen

    Mr. Foxen

    Joined:
    Jul 24, 2009
    Location:
    Bristol, UK
    Disclosures:
    Amp tinkerer at Ampstack
    Are the valves different shapes? Not super unlikely to be same manufacturer, different brander.
  9. Al Florenzo

    Al Florenzo

    Joined:
    Sep 19, 2011
    Thanks for all the replies. Yes, they are indeed different shapes, that's what I noticed right off the bat. It is the first model, but I've never heard of it having auto bias, you sure about that? I know the YBA 300 has autobias, with tons of glowing light on the back panel. Oh well, I'm probably gonna retube it sooner or later. One pair is TungSol, so I might use those to replace the stock tubes in my EBS Classic T90 head before selling it (if they still have juice in them). Ooor would someone advice against that?

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