Mismatched tubes=bad, right.....?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Testudo, Nov 2, 2004.

  1. Testudo

    Testudo Member

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    Clear this up for me. Espacially after reading about Tybone's endless tube-swapping experiments with his Onyx (see thread here ) whatever I thought I knew about the do's and don'ts of tube selection has got very cloudy in my poor ol' brain. So what can you can or cannot do, tubewise?
     
  2. 908SSP

    908SSP Supporting Member

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    Only the power tubes work in pairs. He wasn't swapping any of those. The first, I think was five, were all preamp tubes the last on his list is the rectifier tube.
     
  3. Testudo

    Testudo Member

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    Check out his Sept 4 post:

    V6 and V7 are output tubes.
     
  4. hipfan

    hipfan Member

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    Yeah, that's OK. You can use two different brands of tubes within the same general type with no complications necessarily developing. This Tybone fella is using two different 6L6 variants - no sweat.

    Now, there are different schools of thought when it comes to using *matched* power tubes, whether they are of the same brand or not. Some claim that it is not that necessary to get the best tone. Some claim that matching, within certain parameters, is necessary to best amp performance. I'm not qualified to say which, if either, is correct.

    What I can say is that one of the most hellaciously good tones I ever had was through a pair of terribly matched old Mullard EL34's in a '70 Traynor I picked up. One tube was/is obviously pretty beaten up, but man the tone was good!
     
  5. Testudo

    Testudo Member

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    So the thing to avoid in a 6L6 amp, for example, would be using one 6L6 and one 7581?
     
  6. FlyingVBlues

    FlyingVBlues Gold Supporting Member

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    I believe Tybone can safely do this due to the individual bias and phase-balance adjustment controls the Onyx has for each output tube.

    FVB
     
  7. hipfan

    hipfan Member

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    No, a 7581 is a 6L6 variant, so it would be OK.

    As for the Onyx, yep, if it has individual bias controls, that sure facilitates tube experimentation. That's one reason (of many) I'd love to try the THD Flexi.
     
  8. loverocker

    loverocker Member

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    Seems to me that it's going to depend on the type of tone you like. Well-matched power valves with a well-matched PI (and all the components that surround them) will produce a more properly symmetrical ouput (cleaner). That might sound great, but I likes the asymmetries I get from mismatching (extra distortion). :)

    You do need an amp with separate bias controls for each power valve. Designed in from the get-go this arrangement can let you mismatch valve types, too. The London Power Studio amp lets you mix anyway you want: 6V6 and EL34, etc, etc.
     
  9. Testudo

    Testudo Member

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    I need to revive this thread:
    Can anyone give me an example of a tube combination (in any amp) that would be HARMFUL? I'm not even thinking about tone, just the old adage that mismatching tubes is a bad thing to do.
     
  10. drbob1

    drbob1 Silver Supporting Member

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    Different tube types in an amp with a single bias circuit mean that the tubes may be operating in very different parts of their range. So one may be biased cold (and sound clean and sterile) and the other hot (and melt the plates and short out and take your OT with it). So, if you're going to mix tube types, or use unmatched tubes, it's best with amps that let you set individual bias, second best with a bias tester to make sure you're in parameter range for any given tube...
     
  11. saros141

    saros141 Guest

    I have a stack of old Radio-Electronics and Electronics World* magazines from 1955-1965, the "golden age" of tubes... and they talked plenty about matching back then. Sold 'em matched, too, and guaranteed, at a premium... so the GT approach isn't really new.


    *Ziff-Davis Publishing Company. Yup, that Ziff.
     
  12. saros141

    saros141 Guest

    I was waiting for you to say that. ;)

    1. Those magazines were aimed at hobbyists and technicians alike: the guys who would end up servicing anything that ran tubes. Back in the day, when bands began to play for larger and larger crowds, the guitar amps were not always mic'ed, and the PA amps usually ran tubes too. If they wanted to be heard, they wanted strong matched tubes for optimum power transfer. The Beatles played Candlestick Park with only their AC30s and a pair of 80 watt Altec 1569A tube amps!

    2. Not everyone has the technical skill and confidence to intentionally mismatch tubes for a specific result. Heck, lots of folks are a bit afraid of the guts of their amps, and simply want a no-brainer replacement strategy that will ease their minds, so they can just get on with playing and not worry about failures. If QC is lower today, there's a niche for someone to raise it - GT is just meeting an already existing demand.

    3. Maybe some people want a symmetrical tone from their power section, but they don't have a tube tester.

    4. I've no doubt some GT tubes end up in HiFi gear.

    I'm not necessarily a GT fan... I prefer NOS too. And I'm as intrigued as anyone by what mismatching has to offer. I likes asymmetries too!

    I just don't see a reason to jump on someone who obviously has a passion for tubes, is doing smart business, and is working to keep the technology alive and promote it.

    "What sounds the best is subjective.... they are all a little different" - Aspen Pittman, from a recent article in The Toronto Star, titled "Beauty out of a vacuum", to mark the 100th birthday of the vacuum tube, November 15, 2004.
     

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