Two New Power Tubes for a SC20,… Matching?

Discussion in 'Marshall Amps' started by scozz, Oct 23, 2021.

  1. scozz

    scozz Well-Known Member Gold Supporting Member

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    Do you guys have your power tubes matched? Is there a reason, or is it better in some way to have power tubes matched? Also, does it matter if the amp has only 2 tubes? :shrug:

    I’ve heard people say some totally different things about this. I’ve seen people say there no reason or benefit to have them matched.

    At least one person claimed that an amp could/would actually sound better if the power tubes were not precisely matched!

    And the other sides argument is they should always be matched. Is there a consensus on this here? :cool:
     
  2. Dogs of Doom

    Dogs of Doom >>> Moderator <<< Staff Member

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    I think you're confusing pre-amp & power tubes...

    Power tubes do have to be pretty close. If the tubes are too lopsided for the push/pull circuit, you will get hum. The farther off, the louder the hum.

    You can generally bias each side to make them match, but, then you'll wear the sides out unevenly, whereas if the tubes match pretty well, they'll have a better chance of wearing together...
     
  3. scozz

    scozz Well-Known Member Gold Supporting Member

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    Thanks for the info @Dogs of Doom, no, I’m talking about power tubes, not preamp tubes. Are you saying preamp tubes should be matched?

    I’m not talking about biasing tubes either, this is for a SC20, they’re cathode biases.

    When I put power tubes in a cart somewhere, I’m asked if from the seller if I want matching, that doesn’t happen when I’m ordering preamp tubes.

    So that’s why I’m asking, should I check the box to have the power tubes matched or not?

    https://www.tubedepot.com/products/electro-harmonix-6ca7-eh-power-vacuum-tube
     
  4. GregM

    GregM Well-Known Member

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    Sounds to me like DoD is saying, they don't have to be, but it's better if they are.
    Less noise at higher gain and more durability.
    At least that's what I read
     
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  5. Dogs of Doom

    Dogs of Doom >>> Moderator <<< Staff Member

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    usually pre-amp tubes will ask if you want matched sides in the tube.

    Many stores claim that the PI, which is a pre-amp tube, in the power section, need to be perfectly matched, to feed the 2 ½'s of the power section equally. Some people say that they prefer that tube to be a little off balance.

    Power tubes, should always be matched. Typically, even if you order them matched, they'll not be perfectly matched. On an amp, where you adjust the bias manually, you can balance the sides pretty well & get optimal performance.

    On a cathode bias, the tubes should still be within a certain tolerance, of each other.
     
  6. PelliX

    PelliX Well-Known Member

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    It's quite logical really, your output valves are driven in parallel (to put it simply, room for nitpicking there depending on the exact circuit). Your PI should ideally be balanced (or close, no valve is 100% balanced if you measure closely enough). The rest of the pre-amp valves are used in series, not in parallel, so you can add, remove and replace them however you want.

    What Dogs said, for a cathode biased amp they should be within tolerance. If you can select 'matched pair', do so. It's worth that extra buck or two.
     
  7. Chris-in-LA

    Chris-in-LA Well-Known Member

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    No tubes are precisely matched anyway, and some think that being a little mis-matched makes the amp tone a little more complex.

    I’m confused about why you would ask if it matters that the amp only has 2 tubes.
     
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  8. PelliX

    PelliX Well-Known Member

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    It only has two output valves. Great amp, all the same, though. :applause:
     
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  9. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Right. So why ask if that matters?
     
  10. PelliX

    PelliX Well-Known Member

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    Presumably because there is a notion that it's more important the more output valves you have. :shrug:
     
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  11. ken361

    ken361 Well-Known Member

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    yes matched is best imo I have these https://www.tubedepot.com/products/electro-harmonix-el34-eh-power-vacuum-tube
     
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  12. LCW

    LCW Well-Known Member

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    Matched yes… :p

    366C8EF2-20BD-42C7-8871-DF02C54D9BFB.jpeg
     
  13. marshallmellowed

    marshallmellowed Well-Known Member

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    Never heard of anyone matching preamp tubes, anything goes in the preamp. As for power amp tubes, matched is always preferred in a standard configuration, as the output tubes typically share the same bias circuit. With the Studio amps, I don't think it's nearly as important for the tubes to be matched, but if you're ordering 2 new tubes, why not just order matched?
     
  14. ken361

    ken361 Well-Known Member

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    when you bias a tube say at 32 on one tube and the other is not matched and only can get it at 25 your distortion will probably sound off.
     
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  15. jeffb

    jeffb Well-Known Member

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    Matched preamp tubes help simply because it ensures every tube has the same gain characteristics.

    There are a bunch of new production pres that the gain value varies like crazy from tube to tube to tube of the same exact tube (Tung Sols are the worst I've encountered). If you have a V1 that's low on the gain factor, buy a replacement t hat rates much higher, your tone and settings change. CF and PI I think are more sensitive to gain factors.

    Is it necc? No, but if you want consistency....

    @Dogs of Doom already gave the good word on power tubes. It decreases life expectancy, and increases noise.
     
  16. scozz

    scozz Well-Known Member Gold Supporting Member

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    Thank you very much, this is what I thought but I wanted assurances that it’s correct.
    Bingo! The answer to Chris’ question.
    Right, I had never heard about matching preamp tubes either. That’s why I was a bit confused in @Dogs of Doom first sentence of his first post, suggesting I’m “confusing preamp tubes and power tubes”.

    Ive highlighted a sentence in your post that touches on part of what I thought, but I wasn’t sure of. Thank you for that also.
     
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  17. Dogs of Doom

    Dogs of Doom >>> Moderator <<< Staff Member

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    not necessarily at higher gain...

    If the power tubes are out of balance, the 50/60hz cycle hum will be loud, no matter the gain. At some point, it will be louder than the signal...

    as far as pre vs power tubes, matching, etc., here's tubedepot's JJ 12AX7 page: (pre-amp)

    https://www.tubedepot.com/products/jj-ecc83s-12ax7-preamp-vacuum-tube

    upload_2021-10-23_8-51-40.png

    notice that the tubes are $12.95/ea

    x's 2 = $25.90

    Now, add on all the extras:

    upload_2021-10-23_8-53-34.png

    almost doubles the price.

    Now, in theory, the tubes, if they were any good, in the 1st place, would have matching triodes, high gain, low noise & they'd be consistent in mfgr, so they'd match... (within tight tolerances anyway)

    To charge extra, for things that should be inherent in the product anyway, is a rip-off...

    Find a dealer that offers all that, at no extra charge...

    I've seen posts on here, saying that people have ordered from them, matched, etc., & the tubes were not even close, & trying to get it resolved was a hassle...
     
  18. jeffb

    jeffb Well-Known Member

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    Yep- Tube depot nickel and dimes for all that stuff. They have got worse over the years for matching on the power tubes. Especially if you order from their Amazon store. Last couple of purchases were less then stellar. But they have good sales fairly often, so you can sometimes get a very good deal even when adding in all the extras on the preamps tubes.

    Dougs tubes for ruby/new sensor or for JJ's-Euro tubes are my go-to.
     
  19. marshallmellowed

    marshallmellowed Well-Known Member

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    I see no reason to pay extra for "matched" preamp tubes. Hell, people are putting 12au, 12ax, 12ay... tubes in their pre's to get the balance they want. I guess if a guy thinks he needs balanced preamp tubes in a guitar amp, and wants to pay the prices, go for it (not me).
     
  20. Dogs of Doom

    Dogs of Doom >>> Moderator <<< Staff Member

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    well, for one, in the newer SVT's, you use 3 "pre-amp" tubes in the cathodyne power section. 1 is a driver, that, needs to be balanced & then 2 tubes that need to be matched, or you'll never get the green light bias & the yellow balance done...

    I know that this is the power section, but, the tubes are "pre-amp" tubes...
     
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