myles111 - tube question...

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


  1. nosajwp

    nosajwp Member

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    Myles,

    First of, I wanted to thank you for putting together such an informative website. All of your information on tubes leaves me with a nagging question...

    1. Which tube vendors (that you know of) test their preamp tubes for gain, transconductance, and current output, and reject tubes that don't meet the tube specs for these values?

    2. Same as above, but checking power tubes for low vacuum, gas leakage, grid leakage, and output current, etc?

    I'm asking, because I know current tube manufacturing has a wide tolerance, and I want to buy my tubes from a vendor who checks for all these things, so that I know I will get tubes that are within original specs, even if I have to pay a little more for them.

    Thanks, Jason
     
  2. myles111

    myles111 Member

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    I know GT tests for these factors and Mesa does it on output tubes but not their EL84's which are not rated at all.

    I know the following folks do a great job at testing.....

    Mike at KCA NOS Tubes
    Doug Preston at Dougs Tubes
    Bob Pletka at Euro Tubes
    Tube Depot
    Penta Labs
    Lord Valve



    and there may be a few more in the tube vendors area of my GAB website.

    There are tons of folks that sell garbage.
     
  3. Tallhorses

    Tallhorses Member

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  4. donnyjaguar

    donnyjaguar Member

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    Here's a question. What percentage of current manufactured tubes don't meet minimum specifications?
     
  5. myles111

    myles111 Member

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    There really is no standard for a minimum spec. Some tube testers have that "good-Bad" scale on them I suppose but what "bad" is I have no idea.

    Typical reject rates at GT are 60% or so but the failure can be for many reasons.
     
  6. drbob1

    drbob1 Silver Supporting Member

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    If you check out Lord Valve's catalog, he has listings of what percentage of tubes fail his tests (which include a 24 hour burn in, and whacking with a rubber hammer :) IIRC it varies from 10% (rare) to 40% at which point he gives up on a tube manufacturer.
     
  7. Blue Strat

    Blue Strat Member

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    I love the "hammer test". See how hard you can hit a tube with a rubber mallet without breaking it. Then tell me how you feel about marketing in general.:roll
     
  8. brad347

    brad347 Member

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    yeah i guess "I give 'em all a good stout flick with the index finger" just doesn't have the same ring to it!
     
  9. myles111

    myles111 Member

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    Actually .... most any tube will exhibit a degree of physical microphonics. I have seen many good tubes tossed when people flick them and decide they are noisy. Do they feedback or squeal when the amp is played? Do they rattle internally where this is audible? If not, they are probably good tubes.

    Wacking with a hammer? Well, I suppose there are pros and cons to this. I may be a bit dull and don't see the pro side. On the conn side, I would never want to try this with a nice set of Genelux KT66 tubes! Power tubes do not like this sort of handling and what may have been a fine tube is not all that great after a grid wire slips from banging on it.
     
  10. AdmiralB

    AdmiralB Silver Supporting Member

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    It's interesting to note that GEC ad copy from the '70s ADVERTISED that they hit them with hammers during burn-in.
     
  11. myles111

    myles111 Member

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    Mesa says the same thing in some photos.

    There is hitting and there is lightly tapping.
     
  12. vinni

    vinni Member

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    Hi Miles,

    JJ has put out the KT77 which I use.
    Do you know if GT is going to produce this tube as well?

    Vinni
     
  13. myles111

    myles111 Member

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    GT does sell the JJ KT-77. It is not on the GT website yet but it is on the GT pricelist. The reason it is not on the GT website yet is because I have been lax in getting a photo.

    I have already posted test results on this tube and it is a great tube.

    GT will not be making a KT-77 as far as I know because they already have their own EL34M dual getter EL-34 tube and the two tube are different and each will have it's own tone. There is no reason to build another KT-77 when there is a great one out there already.
     
  14. vinni

    vinni Member

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    Ok thanks!

    Vinni
     
  15. outtahear

    outtahear Supporting Member

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    Geeze ladies.:)...you hit the chassis (or test rig..) w/a rubber mallet to try to simulate any shock failure that would come from "unusual" occurances like a bumped or knocked over amp. Cesar Diaz taught me that 'lil Q.C. move in the early 80s'.
     

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