Matched pairs/quads

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by slhguitar, Jun 21, 2006.


  1. slhguitar

    slhguitar Member

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    How important is it to have your power tubes matched? I have 4 EH el34s lying around, but i dont think they are a matched quad. I want to try my Dual Rec with the EL34s, but only if it wont be harmed. So my question is, will it harm my amp to put in 4 un-matched power tubes for under an hour of use?
     
  2. Blue Strat

    Blue Strat Member

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    No one can say. One group of 4 might be fine, another may not be. All it takes is one VERY out of match tube to cause hum, or to possibly self destruct.

    Do you feel lucky today? Well, DO YA!??!?! ;)
     
  3. donnyjaguar

    donnyjaguar Member

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    You can test how close they are by shoving in one tube at a time and seeing what current its drawing at idle. This is best if its a fixed bias amp, and with 4 tubes this is almost certainly the case. I bet they're close enough for rock'n'roll. :)
     
  4. rockon1

    rockon1 Member

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    I have yet to worry about matching tubes in 25 years of playing. Maybe Ive been lucky but I havent had a failure cause of it.
     
  5. slider313

    slider313 Silver Supporting Member

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    You've been lucky and if you have a cathode bias amp it isn't as critical. If your amp is grid bias with higher voltage on the plates,then it sure would have affect on your tone and the wear on the power tubes.One would wear much faster than the other if they are far apart in current draw.
     
  6. rockon1

    rockon1 Member

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    Just plain old vannila Mesa's,Fenders,Peaveys and Crates mostly. For my personal experience I believe the matching and(dare I say) even biasing thing way overblown. I have been pluging and playing thru these amps since I started(27 yrs) zero problems. Lucky maybe but honesty I dont believe so.I found thia a while back on the topic which supports my own experience....Of coarse these days power tubes are matched for free most of the time.However in a case where you dont have a matched replacement its the same thing.

    FREQUENTLY ASKED QUESTIONS

    by Kevin O'Connor of [​IMG]




    Q: What's the deal with matched tubes? Some experts say they're very important, and these days it doesn't seem to be too expensive to get matched tubes. Then they talk about matched preamp tubes, and I don't know where to get those.
    A: You don't need matched tubes of any kind in your guitar amp. If you are trying to achieve vintage Fender, Marshall, Vox, Silvertone, Gibson et al. tones, then you simply plug in the tubes you have, check the bias and play. No manufacturer of musical instrument amps uses matched tubes, with the possible exception of Groove Tubes.
    As discussed in the TUT-series, matched tubes will drift out of balance over time due to electrical imbalances in the circuit and the different response of each individual tube to mechanical stimulus. Drop the amp and one tube may break while the other survives, even though they were electrically "matched" when you bought them.
    As discussed in this FAQ and in our books, asymmetries in the push-pull output stage, and in the handling of the signal throughout the signal path, contribute to the harmonic balance and thus the warmth of the tube amp's sound. You can build in specific asymmetries, or use unmatched tubes or even different tube types to play with asymmetry.
    Matched triode sections are often cited as "beneficial" in the Schmitt splitter used in most guitar power amps. The circuit is inherently out of balance and has skewed values to restore some semblance of output signal balance. Perfectly matched triodes would offer no actual benefit and would contribute to higher levels of odd-order harmonic distortion. These sound "crisp" in small quantities but are "harsh" in large levels. Again, just as with separate output tubes, the two sections of a dual triode will be quite close in their performance since they are made on the same production line, likely one after the other. There is still the possibility that mechanically jarring the tube will upset one side more than the other, so the expensive matching you think you paid for is lost forever.
     

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