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Half-Tubing

Discussion in 'Amps [BG]' started by Calaverasgrande, Jan 14, 2013.


  1. So this is an old story. Or rather an old trick that I dont hear too much about. I have an old Traynor tube combo that I play my synthesizers through. It's a 2x12 guitar combo, goes by the name of YGL3.
    I recently moved all my music equipment to a new space, and on firing up the amp it sounded kind of off.
    I peeked at the tubes and one of them was off. Not funny off, OFF off.
    So I did the normal thing. I pulled half the power tubes and plugged it into a an 8 ohm cabinet (the previous speaker impedance was 4 ohms).

    The only trepidation I have about this, is that in my experience, Traynor amps brutalize EL34 tubes pretty good. Some sources I have read on the interwebs claim that half tubing is fine, but you have shortened tube life. Conflicting sources claim it makes no difference as long as you double the impedance.
     
  2. Passinwind

    Passinwind ......Charlie Escher Supporting Member

    B+ goes up a little, so a 100 watt amp may measure 60-65 watts with half the output tubes pulled, at least with the particular ones I've measured (Fender and Laney guitar amps).
     
  3. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    The remaining tubes see the impedance they are expecting by you changing the output impedance. They'll work quite happily.

    Your sources, I suspect, pulled the tubes but did not compensate by changing the load.
     
  4. Passinwind

    Passinwind ......Charlie Escher Supporting Member

    +1

    I ran my Laney for a couple of years that way.
     
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  6. jastacey

    jastacey Supporting Member

    Feb 8, 2009
    Houston,Tx
    If I'm not mistaken, the bias scheme on the old traynors is done in a different way, there is 100+ bias volts and when taken out of standby it slowly drops to the set bias voltage, removing tubes my upset this bias Scheme
     
  7. Hi.

    Or the source forgot to at least check whether the bias was still in the range.

    That's about the only thing giving grief with the "pulled" tubes.
    IMLE Marshalls (+clones) are very forgiving, the bias usually stays within' the parameters, but I have no experience about the various other bias circuits behaviour when used in this manner.

    Regards
    Sam
     
  8. M. Owen Santy

    M. Owen Santy Banned

    Aug 10, 2011
    Springfield, MA
    Disclosures:
    Michael Tobias Designs Kingston Series & Traynor Amps Artist
    I would personally just change the tubes. It's not that expensive compared to even the slightest chance of loosing that old Traynor.

    They are selling @ $700+ on EBay - and even more on the Vintage market depending on condition. Can do with reasonably high quality JJ's from http://www.thetubestore.com/EL34-6CA7-Tube-Types under $70.00 US. A small investment for an already valuable amp that's only going to become more valuable - unless of course it gets fried.
     
  9. B-string

    B-string Gold Supporting Member

    Deep fried Traynor, sounds like a county fair dish.
     
  10. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Just make sure that you remove one push and one pull tube. You DON't want to remove the pairs (V6 and V7) or (V9 and V10).

    If the two remaining tubes sound good with the 8 ohm cab, enjoy the tone.
     
  11. I puled the rear pair. They are set up in a kind of square (well a parallelogram) with one pair behind another.
    I really need to move teh "good" tubes to the rear sockets to confirm it is a bad tube and not a bad socket.

    Yes I SHOULD just buy a new quartet of tubes. But I just had my car go toe up on me a few weeks ago so I am under self imposed austerity measures until I can afford another used car. Plus it's kind of hard to get my amp to a tech to be biased for a new set.
    I know I can run them without getting the amp rebiased. But it sounds better.
    Besides, my bass amp needs new tubes too! My next 3 paychecks already spent.