Marshall JCM 800 2203 no distorition

Discussion in 'Marshall Amps' started by PeeJay, Oct 15, 2021.

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  1. PeeJay

    PeeJay New Member

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    Hey.

    Ive recent got a Marshall JCM 800 2203 from my late father. Its with a Marshall 1960 Vintage cab. Ive only played on combos, so I have not much experience with this one.

    Heres to the problem. No matther how I twist and turn the knobs, HI or LOW, I cant get any distortion out of it. Ive searched some youtube reviews on this amp and it sure got alot of crunch to it. Im guessing it needs some sort or repair. Anyone knows what might be wrong with this amp?
     
  2. FutureProf88

    FutureProf88 Well-Known Member

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    Have you tried new preamp tubes?
     
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  3. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Preamp volume to 10. Master to whatever sounds good to you. That should be pretty distorted.

    If not...the first thing to check is the three preamp tubes. Wiggle them in their sockets, be sure they're fully seated, swap them around, test them any way you can or just put in others.

    If it's still too clean sounding, it's time to take it to an amp tech.
     
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  4. DreamerDeceiver

    DreamerDeceiver Well-Known Member

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  5. PeeJay

    PeeJay New Member

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    I havent tried anything but the obvious. Preamp on 10, but no its still all clean. I have absolutly no experience with this, but should I take a check anyway at the tubes? Yeah I have a tech, I was just hoping to pinpoint whats wrong with it first. Thanks for answers!
     
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  6. neikeel

    neikeel Well-Known Member

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    There are a few things that spring to mind.
    Has it been sitting unused for a while? Is it stock or modded?
    The contacts on the input switching jacks may be dirty so you are not getting the cascade between the two halves of V1. Try spraying deoxit into the jack socket and inserting a jack into them a few dozen times.
    Next replace V1 (first small valve - furthest from the bigger output valves) with a new ECC83/12AX7. If that does not work move down the line replacing each valve in turn with the new one.
    If that does not work it will probably need looking at by someone who knows what they are doing!
     
  7. PeeJay

    PeeJay New Member

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    Ive tried to switch some of the tubes, checking if they are in place e.t.c. I cant find anything wrong so Im going to bring it to my tech tomorrow. Thanks for your answers.
     
  8. Leonard Neemoil

    Leonard Neemoil Well-Known Member

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    @PeeJay, the first thing I'd check is whether or not it even has 12ax7 tubes in it. Maybe dad replaced them with lower gain tubes...
     
    Last edited: Oct 15, 2021
  9. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Make sure that you try both input jacks. One is significantly louder than the other. If you have the pre-amp up to 8 and are plugged into the High sensitivity jack and don’t have distortion, something is definitely wrong.
     
  10. Derrick111

    Derrick111 Well-Known Member

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    Maybe he had it modded or used a different (lower gain) tube in the preamp. Check that all three are 12AX7s. If they are and swapping in known good working ones doesn't fix, then you may need to bring it by a shop. Also be sure you are plugging in the High input, not the Low.
     
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  11. Matthews Guitars

    Matthews Guitars Well-Known Member

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    How about cracking it open and posting a few clear pics of the insides?

    It might be something as simple as someone changed resistor values to make it a totally clean pedal platform.
     
  12. Solitary49

    Solitary49 New Member

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    I had the exact same problem with a 1987X that I bought without playing it first. I know, bad idea, but for the price, it was worth the gamble. I tried everything that others have suggested here and nothing worked. It would get extremely loud, but distortion. Everything looked good inside with no obvious abuse. Long story short, I replaced the power tubes and pre-amp tubes and it roared back to life! A good set of tubes aren’t too expensive and a cost of tech to bias the power tubes (unless you can do it yourself) is worth it.
     
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  13. jamvu

    jamvu Member

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    Solitary49 is likely right. An old amp sitting around for years could just need some new tubes. That thing should be a tone monster.

    Jamvu
     
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  14. pedecamp

    pedecamp Well-Known Member

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    Look at the preamp tubes, maybe your dad substituted the 12AX7's with something low gain, report your findings. Tell us what power tubes are in it while youre looking. Also at some point check the bias, it should be around 76mA give or take.
     
  15. pelican

    pelican Member

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    most likely the jack
     
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  16. Derrick111

    Derrick111 Well-Known Member

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    That is another one I forgot about on the MV amps... clean the contacts on the little switched contacts of both input jacks. To do this, I usually cut few thin strips or paper (preferably the thicker stuff like a business card - junk mail has lots of it) about the thickness of a match (so it can fit in the jack contact), and grab it with some needle nose pliers, then get it between the jack switched contacts to slide it out - removing dirt/contaminants. I insert a jack tip till the switch contact opens, then place the paper in there, then remove the jack so the switch closes on the paper and simple slide it out which will clean it great. Bonus if you have an electronics cleaner like you use on your controls (DON"T USE WD-40) or even you could use rubbing alcohol.
     
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  17. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Tubes don't go bad when just sitting there unused. That's why new old stock tubes are so highly prized!

    The connections may get crusty from rust or corrosion or dirt, but as long as the glass envelope is intact and undamaged,
    the tube itself isn't going to wear out when it's cold and dark.
     

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