Marshall Valvestate 8100 Questions

Discussion in 'Marshall Amps' started by TheCommonwealth, Mar 16, 2010.

  1. TheCommonwealth

    TheCommonwealth New Member

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    Hey everyone, I've been reading these forums for quite a while, but just recently got around to becoming a member and have a question about my amp.

    It's a Marshall Valvestate 8100 (not sure about the year, I bought it from a friend who inherited it). I recently decided to change out the preamp tube (Marshall ECC 83) for a new one. I brought the amp into a reputable shop in Portland, Oregon and had three or four of the employees there look at it, all of whom decided that the replacement tube would be a 12AX7 Tung-Sol. Following their instructions for the installation, I carefully installed it and let it warm up slowly for a good 30 minutes before playing through it at a lower volume. It sounded absolutely fantastic for about five or ten minutes, at which time I decided I wanted to hear how my Les Paul sounded through it. I powered down the amp, plugged in my other guitar, and powered it back up. Then something odd happened. The distortion was very quiet, almost inaudible. I turned it up a bit, and still it remained quiet enough that I could barely hear it. I decided to troubleshoot a bit and powered it back down, and installed my old tube, which worked fine (it was as loud as it was supposed to be). I reinstalled the new tube again and the same problem persisted. I thought maybe the tube was a dud, so I took it back to the shop and got a replacement, which again has the same problems.

    With both new and old tubes, the clean channel sounds fine, just as loud as it is supposed to be. Do they keep selling me the wrong tube? They look almost identical. They are the same size, etc. although the insides of the tubes look a bit different. The odd part is that with the new tubes installed you can actually hear the distortion, and it sounds fine, it's just very VERY quiet even at very high volumes. The music shop that I've been buying from is over an hour away from where I live, and it's growing very tiresome (not to mention expensive) driving up there to exchange items so often, but the music shops in the town I live in are pretty useless.

    Thank you in advance :) If I left out any crucial information, please let me know.
     
  2. Jesstaa

    Jesstaa New Member

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    Were both the new tubes Tung-Sol's?
    If you can be bothered, take it up there again and try other brands of tubes.
     
  3. Large_Filter_Cap

    Large_Filter_Cap Member

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    I have the exact amp, and have had the exact problem. Valvestates are decent middle of the road Marshalls but are notorious for these sort of things. Like most amps I think, they need to by wrestled around with and to set them straight...

    I use the 12AX7, and I have never replaced the tube in 15 years (but I guess a tube change wouldn't hurt either!). I have not experienced the same distortion problems as you have with the tube swapping situation, but in your case if the old tube model works, just keep that in, and stay with it if is sounds good.
    I found that in my amp, the two large grey resisters exactly on the right of the tube produce too much heat, and perhaps the heat radiating from them can overheat the right side of the tube and negatively influence the distortion quality.
    I straighted these two or three resisters so they were more erect, instead of their original slanted-to-the-right setting on the board.
    If you experience any crackling at all in your pots, then spray them down with a good contact lubricant; also spray the jacks, switches, and buttons.

    I found after I did this, I have never experienced any distortion bleed off or volume changes anymore, and the amp is in great order.

    check to see if those grey resisters are running too hot. Also when you try using the 12ax7 tube, check to see if that is running too hot. You should be able to touch it comfortably and feel a slight warmth, if it is uncomfortable warm/hot, then it is overheated and something is up.
     
  4. TheCommonwealth

    TheCommonwealth New Member

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    Both of the new tubes were the same model Tung-Sol 12AX7s.

    I took the amp in to a tech friend of a friend, and he said that the shop is just selling me low quality, non-tested tubes. He also showed me a site that sells high quality, tested tubes for about a quarter of the price.

    My game plan today is to drive back up again (sigh) and bring my amp with me to the shop, with the new Tung-Sol installed and show them the problem, then replace it with the old working tube to prove that the amp still works and that they are selling me low-end products.

    Checking the transistors is a wonderful idea as well. I actually have noticed a decent amount of heat emanating from my amp when the case is off, I've just never pinpointed it.

    The worst part about this whole situation is that the first new tube that I installed teased the hell out of me by sounding amazing for about 5-10 minutes, lol. I know once I get one that works correctly the whole setup will sound brand new.

    I just hope that the music shop doesn't give me too much guff when I go in to return my second tube in 2 days :p I suppose worst case scenario is that I'll be out $28 (yeah, know it is quite a bit for a Russian made tube, but I'm new at this).

    Thanks for your help guys
     
  5. thrawn86

    thrawn86 Well-Known Member

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    For $28, you're pushing into the realm of NOS tubes instead of CP. That might be the ticket.
     
  6. surface54

    surface54 Well-Known Member

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    i had a similar problem, but not exact. there are two fuses on the board F1 is the tube socket fuse, and sometimes tube swapping can blow those fuses.
    so my suggestion, get the right tube in there, either it be your old one or a different one, and if it works dont touch it anymore! if you blow that fuses its ALOT of labor replacing it.
     
  7. Large_Filter_Cap

    Large_Filter_Cap Member

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    The transister/heat sink area should not be hot, it should not even be warm; mabye more like a touch warmer than the ambient room temperature. If they are hot, then that is a problem. Check out those grey resisters...
     
  8. TheCommonwealth

    TheCommonwealth New Member

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    So, I went back up to the shop with my amp and the problem tubes, and we eventually got to the root of the problem. It was the correct type of tube, but for some reason that brand was just not working.

    The tube that did work was a Mesa Engineering 12AX7 ECC 83. :D

    The whole reason for changing the tube in the first place is that the distortion was starting to get very odd sounding no matter how I had the settings. Individual notes played with the distortion on just kind of bled together and sounded pretty horrible. The new Mesa tube sounds great though, the distortion is nice and punchy, and the amp is louder than it was previously.

    Thanks everyone for your help!
     
  9. surface54

    surface54 Well-Known Member

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    rocking!!
    those valvestates are beasts if you can tame em.
     
  10. guvnor99

    guvnor99 New Member

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    I just bought 2 of these heads, thanks for your posts! Also picked up 2 8412 cabs.
     
  11. TwinACStacks

    TwinACStacks New Member

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    :) Stupid question but did you clean the pins and socket contacts FIRST with some cleaner? It can simply be a contact problem. Tubes/sockets can conform to each other when in contact for that long of a period. The new tube might not be making proper contact as the pins aren't exactly the same as the old tube. This scenario has caused problems for more than one tube amp owner.

    :):) TWIN
     
  12. geeski2005

    geeski2005 New Member

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    Folks following on from this thread I'm trying to replace the preamp tube on my 8100 head but I'm struggling to get the old one out. It appears to be shrink wrapped about 2/3's the way up in black rubber coat and when I tried to remove it it wouldn't budge. I'm afraid of trashing the connections to the board. Did you guys have similar issues removing your tubes or is there something I'm missing.

    Thanks.
     
  13. surface54

    surface54 Well-Known Member

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    ive never heard of a shrink wrap around a tube
    for mine there was only a metal brace that goes on top of it you move to the side and the tube pulls out
     

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