Power tubes matched?

Discussion in 'The Workbench' started by Emtbreid, Aug 31, 2019.

  1. Emtbreid

    Emtbreid Well-Known Member

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    Need some assistance please!

    I recently ordered a quad of EL84 tubes from a store, and requested a matched set. They arrived today, and there is a sticker on each side with a number... says bias point underneath. 3 are labeled 29, but one is labeled 28. Is this in fact a matched quad?
     
  2. marshalltsl

    marshalltsl Active Member

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  3. john hammond

    john hammond Well-Known Member

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    -very matched.
     
  4. Emtbreid

    Emtbreid Well-Known Member

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    Thank you sir
     
  5. Lance Chambers

    Lance Chambers Well-Known Member

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    If you use a set of tube socket probes with meters (Eurotubes, etc.,......) you will find they are indeed spot on. I use four probes and meters simultaneously so I can monitor the bias adjustment in real time. The Biasmaster unit will not do that. It will only show one socket at a given time.
     
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  6. LPMarshall hack

    LPMarshall hack Well-Known Member

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    I’ve never gotten a straight answer on the internet on whether power tubes need to be matched or not. Half say yes, half say no.
     
  7. Emtbreid

    Emtbreid Well-Known Member

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    I’m going with yes, it’s better to. What I was looking for moreso was whether the set I got was matched, but that’s been answered.
     
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  8. LPMarshall hack

    LPMarshall hack Well-Known Member

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    I tend to agree they should be matched as well.
     
  9. john hammond

    john hammond Well-Known Member

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    I’ve never gotten a straight answer on the internet on whether power tubes need to be matched or not. Half say yes, half say no.

    I wonder if they actually understand what theyre agreeing/disagreeing with? or just repeating stuff they've read?

    the answer is not difficult to understand.

    if you mismatch( enough ) , the amp will hum...and give you better harmonic output...the more mis-matched, the more harmonic variation, and the more hum. mismatching tubes for the harmonic benefits is like doing a deal with the devil.
    if you match, there is no hum...( there will still be some hum coming from the amp for other reasons, they are gloriously imperfect things.)
    i always mismatch, always. so on a 50 watter one tube will be set at 39ma, the other 32.
    I love it.
    I use 2 different brands in the same amp for enhanced effect...with four tubes, ill use four different brands if theyre hanging around.

    edit- just remember, when you're playing, there aint no hum.
     
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  10. Lance Chambers

    Lance Chambers Well-Known Member

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    When Zakk Wylde was asked how he controls the noise and feedback onstage due to the high volumes he said never stop playing.
    :shred:
     
  11. john hammond

    john hammond Well-Known Member

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    hahaa

    i should add here i said i always mismatch on my own amps, i got a bit carried away, if i get an amp to sound just perfect, I'll try and leave it as it is at that time. Some of my own best amps have matched tubes, ( not too matched i hope)
     
  12. Emtbreid

    Emtbreid Well-Known Member

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    Other than reduction of hum are there any other pluses of using a matched set?
     
  13. john hammond

    john hammond Well-Known Member

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    Techs will use them so they can minimise comebacks, due to hum.
    But for a guy who just mucks around with his own amps, no.
    if you're mucking around with mismatched tubes, remember to try and mismatch them properly, 5ma difference is for pansies.
    And most important of all, make sure the one that's reading the highest number ( the hottest one to touch) is identified as quickly as possible, and THAT tube is the upper limit.

    - use a white marker to write on the tube base..what the number is that your thing that you use to measure bias current is reading..nice big letters.
    this will help you later if you need to remember without re-measuring, also this allows you to monitor drift..there is an irony there , so many matched tubes are no longer matched after a while due to drift.
     
    Last edited: Aug 31, 2019
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  14. Emtbreid

    Emtbreid Well-Known Member

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    Got it, that was very informative, thank you !
     
  15. john hammond

    john hammond Well-Known Member

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    prob. been done before.
    experiment.
    get transformer with 6.3 divided by 1.3 = 4.8v taps.
    say..10amp?
    so 4.8vac taps go into rectifier diodes ( high rated ) then into a 5000uf? cap.
    = 6.3vdc. ( some experimenting would be recommended here..maybe 4.68v..maybe 4.73v etc..you really do want precisely 6.3v at the end..under full load)

    feed this 6.3vdc into all your heaters..

    no more heater hum from preamp tubes, no more need to bias tubes for hum.
    in fact, you can now use your bias pot to tune up some harmonics.
    its like a harmonic chicken cooker?

    amp is much quite-er too.

    this idea is growing on me, its hot damn alright.

    i dont want to disappoint anyone, but uh..our amps are made to a budget.
    manufacturers couldnt be bothered to do any of this stuff because you cant add any shiny pots onto the face of the amp by doing so.
    new amps are all about new knobs.
    you get get an easy to find 10 amp 5vac transformer, and just wind off the tap until it reads what you need it to read.
    the mod would cost you about thirty lousy bucks maximum, more like 20.

    edit- brown it up a bit
    have multiple taps...4.73..4.5..4.3

    brown up all your filaments evh style.

    this solves the problem of having no knobs.
    randall would patent this ( he's done that before successfully , several times- just patent something thats been around forever)
    randall, you're welcome.
     
    Last edited: Aug 31, 2019
  16. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Straight answer regarding tube matching: Yes, it matters. The more imbalance you have between the tubes on each side of the output transformer, the more hum you will get. The hum cancelling effect works best when tubes are matched best.

    In the case of amplifiers that use ultralinear output transformers, tube matching is MORE critical. This is why Fender included tube matching controls on the back panel of all their amplifiers that used ultralinear transformers, and some that didn't. If this control is present, it can be used to make the amp dead silent, good enough to satisfy any recording engineer, when it comes to hum level, even if the tubes are significantly unbalanced.

    You may have noted that if you ever get a red plated power tube, it's accompanied by a hum coming out of the speaker. That's due to the imbalance caused by a shorted tube.

    If your power tubes don't cause any significant amount of hum, they're matched well enough.

    Be aware, you don't have to have a perfectly matched quartet in your amp. Two matched pairs that are distributed symmetrically will be sufficient. Not ideal, but sufficient.

    If, for example, you had a pair of tubes that are matched at "15" and another pair that's matched at "30" then you can install them in 15-30-30-15 order or 30-15-15-30 order.

    In fact, there's no reason why you can't have them in 15-30-15-30 or 30-15-30-15 order. As long as there's a 30 on each side of the transformer and a 15 on each side of the transformer, you're good to go.

    What you don't want is a big mismatch between the sides of the output transformer. 30-30-15-15 is a no go.
     
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  17. Guitar-Rocker

    Guitar-Rocker Well-Known Member

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    Very few, if any OT's are wound precisely with the same resistance on both primary coils, from the git go, so "matched" is always off a bit.
     
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  18. john hammond

    john hammond Well-Known Member

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    - Only so if a little hum bothers you, single coil pickups are a lot worse, and that doesn't bother me in the slightest.

    I am eating ass sandwich on the dc to heaters hum cancelling proposal with the ' harmonic chicken cooker'.

    Unfortunately, for my brilliant idea, it will only work in class 'A'..not 'AB.'
    it WOULD work in class ' AB' if I was supplying pure d.c to the plates via batteries, instead of heaters.( lets see, thats only 20 car batteries in series..)
    A rectified filtered dc supply for output tubes would mean a quite-er amp, but not much.

    This guy ' sluckey' on this thread in the link explains it nice and smooth, Mathew guitars hit it right on the head though, the 120hz ripple goes through the output transformer and into the speaker.

    According to sluckey, the hum originates at the filters because they simply aren't perfect at getting out A.C

    https://el34world.com/Forum/index.php?topic=21533.0
     
  19. john hammond

    john hammond Well-Known Member

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    - here we enter territory where a person is telling another what to like, and what to not like.
    please don't get the idea i'm lining you up for a pissing contest mathew guitars, you're a clever dude, to be respected.
    People get into these pissing contests and all they're doing is cut an pasting, typical internet BS back and forth and the punters watching learn nothing.
    I say, if there is no danger to the equipment, if there is added harmonic content ( you may want to check that out, no one denies it )...then why not?
     
  20. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Balance for power output.
    You bias to the hottest tube if all are not equal. The tube with the colder bias will put out the least power at volume.
    If they are within a couple mA it is no big deal but a farther spread can allow hum and will drop overall power output.
     
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