Marshall SC20H weird problem! I am getting desperate so please help...

Discussion in 'Marshall Amps' started by CroTone, Mar 4, 2021.

  1. pedecamp

    pedecamp Well-Known Member

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    The amp has 3 preamp tube positions, pop your good tube into each slot one at a time and try the amp each time, doesnt matter what order.
     
  2. CroTone

    CroTone Active Member

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    Ok! Will do and will report back. Thank you so much!!!:wub2::hug:
     
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  3. ampeq

    ampeq Well-Known Member

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    Yep, try tubes 1st. I have no idea why the effects loop would do such a thing to the amp, I'v never even heard of such a problem.
    But if you can don't wait, have them replace it asap. If it's a good outfit you should have no problem. Sorry to hear about that, sounds like my luck!
    This is why I use Sweetwater. If something like this happens I will get a new one within 2 days, then they pick up the bad one. I had a bad Mesa and what I thought was a bad Marshall and both were replaced within 1 day. They also will beat any price, in fact they have always given me a better price than anything I have seen.
     
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  4. solarburnDSL50

    solarburnDSL50 Well-Known Member Platinum Supporting Member

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    My neighbor years ago laughed at how the shit(amps) I got always broke down or arrived that way. Then I had to return them. Mine were all mail order. It was daunting at first but learned how simple the process is and that I always got taken care of.

    Now if there is a hint(short of a bad tube)I contact them and make them take care of me. And that means telling them I found a bad tube in the amp. They send a new tube. Sweetwater has the best CS. I also you zZounds. Both of these have made sure I'm a happy customer. And the process is simple, fairly quick and usually painless other than controlling my buyer remorse.:D

    I think it's prolly a bad preamp tube. If it turns out it's not? Make them take care of any issue.
     
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  5. Jethro Rocker

    Jethro Rocker Well-Known Member Silver Supporting Member

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    What you have done is bypassed the preamp so you knpw the power section is working. So likely a preamp tube, probably V1 or V2 but again, other thkngs could arise i the preamp section. Input jack issues, a partial short at the jack etc.
    Try pre tubes first.
    Don't worry about the SC20 as a model though, most of us have had no issues with ours.
     
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  6. Old Punker

    Old Punker Well-Known Member

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    I have to admit that the packaging system used by the Marshall factory is the best I have ever seen. Mine was in the original factory box from England when I got it. It had the most elaborate and well thought out suspension and anti-shock system ever!
     
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  7. Maggot Brain

    Maggot Brain Well-Known Member

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    If you recieve a tube amp by mail it's wise to check to make sure all tubes are seated and undamaged prior to firing it up. My first thought was a loose or bad preamp tube by your description.

    Mail and package handlers are there to earn a paycheck, they don't give a fk about fragile stickers. Chuck it, toss it, get the job/day over with fast. Those tubes can rattle and knock loose pretty easy.
     
  8. marshallmellowed

    marshallmellowed Well-Known Member

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    Did you put a jumper from the FX Send to Return, as I suggested. Plugging a guitar into the Return only tells you that the power amp is working. Putting a jumper from the Send to the Return will check the FX loop jack contacts. I'd to that, before replacing tubes, as it can be done very easily. If there's no sound with a jumper in the FX loop (loop on), then I'd move to preamp tubes.
     
  9. CroTone

    CroTone Active Member

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    Ok, guys, so I took one 12AX7 tube that I know is working from the Origin's preamp and then I removed the first one on the left (when you are facing the back of SC20) from the SC20H (the one and only that is protected with metal cap)--is this V1? I am always confused by the ordering.
    Anyhow, the thing now works...it looks like that tube was faulty! I've tested it for a few minutes and the amp does what the Marshall was supposed to do.
    Should I be worried about anything else, maybe replace the remaining preamp tubes? They are Marshall JJ's dated to 2019.
    Obviously, I will need to be getting some more tubes anyways because now my Origin lacks one.
    I have no spare (working) tubes lying around.

    I deeply appreciate all of your comments and I would wish to thank you all for the great help!

    Cheers!:band::)
     
  10. solarburnDSL50

    solarburnDSL50 Well-Known Member Platinum Supporting Member

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    Yep you replaced V1 which is closest to the guitar input jack. That can tell you where V1 is. Plus it's the only one with a shield in this amp.

    Good job man. If the others are not noisy/staticky leave them in. Always good to have spares. I'd make the store send you a new 12AX7 explaining it had to be replaced as the amp was not working. If they ask which one you tell them V1 preamp tube.
     
    Last edited: Mar 5, 2021
  11. Chris-in-LA

    Chris-in-LA Well-Known Member

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    V1 is usually the tube closest to the input jacks.
     
  12. Madfinger

    Madfinger Well-Known Member

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    Shippings sometimes not good for amps/ tubes. Purchased a 68 Princeton Custom RI online & delivered from a reputable shop a few years ago & was bitterly disappointed, like devastated, until I pulled & re-seated the tubes. It's a keeper.
     
  13. CroTone

    CroTone Active Member

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    Hey, thanks for dropping by!

    Other than what we would presume as normal "static" hiss that is present and that goes up as I turn the volume up and drive the preamp harder or get closer with my single coil telecaster, I did not notice anything out of the order so far.
    There is no crackling noise, any type of "popping" sounds when I switch from standby to any of the attenuator modes, or anything like that.
    Amp operates normally on the high and low input jacks as well.

    So I guess the problem, in the end, was in the bad preamp V1 tube, and hopefully, that's the end of my drama with this one.
    I did call the guy from the store to make sure we are all on the same page, I did tell them that the amp came with the bad preamp V1 tube and that I will likely take care of that since we identified the problem is with V1. I basically told him if this is all there is to a problem, I will keep the amp and if everything OK from now on I won't be giving them more calls or requests, however, if anything gets complicated I will send them back the whole thing. They were, of course, OK with that so let's hope that this is all to it. I like to keep things transparent and be fair and square so that they know I haven't received this one in optimal shape as I should have as a customer since this is a brand new item under warranty

    Speaking of preamp tubes, do you guys have any specific recommendation for this type of amp or any good combination of tubes that you might attest works well with this circuit?
    Is there anything I should pay attention to?
    I am mostly a hard rock type of guy (that's why I bought this little beast) so mostly oriented towards good and organic distortion sound.

    Since I am in the market for new tubes, obviously, would like to hear your recommendations as Marshall experts!

    Thank you!:jam:
     
    Last edited: Mar 5, 2021
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  14. CroTone

    CroTone Active Member

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    Yes, tube amps are of course sensitive machinery and I can totally see that things can move in the transport, especially if tossing, etc.
    But I am happy that the fault was likely the V1 tube and that should be an easy fix.
     
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  15. CroTone

    CroTone Active Member

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    BTW, the most important thing I did not comment on...and that is the sound.
    It sounds phenomenal...and cleans up really nice.
    I am a single-channel guy and with this one, I can jump around to a myriad of sounds just by playing with the volume knob. It is truly a classic!
     
  16. fitz288

    fitz288 Apprentice Fermi's Paradox Analyst Silver Supporting Member

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    Well I would recommend... Oh, wait, you asked for expert opinions, never mind.

    If you're not looking to change anything tone wise, or gain wise, just go with a JJ ECC83 / 12AX7 like the stock tube.
    They are inexpensive and can be found just about anywhere that sells tubes.
    Get a pair and have a spare.
     
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  17. CroTone

    CroTone Active Member

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    I meant more knowledgeable than me on this topic, and that's pretty much the whole forum...so yes, that makes you an expert.
    More than myself for sure!
    Thanks for the tips man! My local store only has JJ's, nothing else lol
    However, I can always purchase something else online.
    Cheers! :cheers:
     
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  18. dro

    dro Well-Known Member

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    Only Marshall I've ever had any kind of issue with besides general maintenance. Is my Mini Jubilee. Maybe the 20's have a glitch.
     
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  19. matttornado

    matttornado Well-Known Member

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    What attenuator do have that uses tubes?
     
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  20. fitz288

    fitz288 Apprentice Fermi's Paradox Analyst Silver Supporting Member

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    I'd tell you where I buy my tubes, but someone would probably rip me a new one (again) about making Bezos richer.
    Last tube I bought was direct from Antique Electronic Supply (tubesandmore.com) and the USPS lost it for over a week.
    At least the free shipping from "the vendor that shall not be named" is reliable.
     
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