The Dsl1l00h Mod To End All Mods..

Discussion in 'Marshall Amps' started by bobpick68, Feb 18, 2019.

  1. bobpick68

    bobpick68 Well-Known Member

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    NOS GE 12AT7's in V1 and V4. Turn treble knob to just below noon. Bias to 83.3 per side. V30's.

    Best amp tone I've ever played through including amps that cost 3x what this amp goes for. Both channels.

    Takes it out of "high gain" territory but the tone and feel gained (pun intended) is immense!
     
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  2. BftGibson

    BftGibson Well-Known Member

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    i have to get you my schematics to mine, have friends who build & mod like crazy..my 100h was made to match my jmp50 on classic green, jcm800 thump on Ultra green & SLX on red..it does it darn close and gigging is a dream..Classic chan can be run plexi style with boost or wicked crunch on its own. They did a plexi mod on classic, choke, sozo caps everywhere applicable & vol tapers..gain is usable from 1 to 10 now and it is a quiet amp..I use 1960bv cab loaded with jcm800 era gt75(65 ish) & earliest made Vintage in X pattern. I know exactly what you mean about this amp. Congrtas on tone seeking results !!
     
    Last edited: Feb 18, 2019
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  3. BftGibson

    BftGibson Well-Known Member

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  4. Bloodrock

    Bloodrock Well-Known Member

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    That’s really hot bias for a dsl! What’s your plate voltage?
     
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  5. bobpick68

    bobpick68 Well-Known Member

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    Thats mv not ma. I just used the 3 test points and my multimeter. Marshall suggests 90mv but I didnt like how it sounded til I got to around 83-84. Settled on 83.3 per side.
     
  6. Bloodrock

    Bloodrock Well-Known Member

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    Volts/amps are the same as measured at those test points. You need to test your plate voltage. Marshalls specs for the bias on the 2000’s was WAY too high back in the day. That’s why so many sounded like shit and burned up tubes and PCB boards.
     
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  7. bobpick68

    bobpick68 Well-Known Member

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  8. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    yes, 90/side 45/tube is too high...

    the 70% rule is much better, but, anyone that has really messed/tweaked, has found their own sweet spot. Ironically, many people like it way cooler than 90, & closer to 60. I tend to like most of my Marshalls at around 78/side 39/tube. Each amp is a bit different though & so bias accordingly. Note that the higher the bias, the quicker you fry tubes....
     
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  9. Moony

    Moony Well-Known Member

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    Yes, the hotter the bias the less time the tubes will last.
    But that was not the reason, why the pcbs burnt up.

    Take a look here:
    http://www.lynx.net/~jc/TSL122.html (scroll down a bit)
    https://drtube.com/modifications/jcm2000-stable-bias-mod

    With 1 Ohms bias resistors mV should equal mA.

    I wouldn't bias a DSL that hot either - but the OP had two 12AT7 in his amp, which are not the best choice for that design - you'll loose a bit gain with these and maybe he compensates this with just a hotter bias.
    However, if you don't see any redplating on the power tubes, it should work fine.
     
  10. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    I find that using ECC81 change the tonal characteristic of most amp's designed for ECC83 in a bad way. If I want to drop gain, I'd opt for running all 5751 tubes, rather than swapping a single tube out for an ECC81 or 82...
     
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  11. bobpick68

    bobpick68 Well-Known Member

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    Sounds phenomenal to me. Best amp tone I've ever heard I wasnt kidding.
     
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  12. Moony

    Moony Well-Known Member

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    I agree, I never had one single amp, where 12AT7 or even 12AU7 have improved something.
    5751 are ok, I would consider the newer JJ ECC83MG, too - would prefer these over 5751 if you can get selected ones. They are also not as dark sounding as the regular JJ ECC83S and really had surprised me in a good way!
     
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  13. ken361

    ken361 Well-Known Member

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    the 40 c is best at 32 they dont need to be hot since its preamp distortion !! set it 60% and put the tubes back in! lol. at7's are horrible IMO it neuters the tone. Thin and less gain :(
     
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  14. Moony

    Moony Well-Known Member

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    If your powertubes show no redplating, you'll be fine. They could need a change sooner than with colder bias - but you won't damage anything of your amp and if you like the sound now, then go for it!
     
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  15. Clifdawg

    Clifdawg Active Member

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    This is slightly left of the topic, but this tube swap intrigues me. Is there a way to drop the gain a little on only the red channel of a DSL40C with a 5751 tube or tubes? If so, what position(s) would I put them in? I'd like a little more usable gain with the Lead 1 setting for rhythms (Lead 2 has more gain than I'll ever use, I rarely push it past 4 on the dial).
     
  16. charveldan

    charveldan Well-Known Member

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    You can always just turn down the gain.
    Stating the obvious.
    12AT7's sound like dogsh*t in Marshalls.
     
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  17. Moony

    Moony Well-Known Member

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    If you want to lower gain on the ultra channel, you could try a JJ ECC823, that is a hybrid tube, first triode is 12AX7, second is 12AU7. V1b is afair a gainstage only for the ultra gain channel, so you could put that tube in V1.
    But honestly I wouldn't do that.
    The DSL40C isn't a amp with real two separate channels, just with one channel and added gainstage for "ultra channel".
     
  18. Moony

    Moony Well-Known Member

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    Yes, that's a way to tame the gain.
    I would do that to the point where I have the lowest gain I need - and then probably boosting with an OD pedal in front of the amp if more gain is needed.
     
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  19. marshallmellowed

    marshallmellowed Well-Known Member

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    Maybe it's the sound of the output tubes running way too hot that you like. Bias the amp at 64 to 70 ma per side (as it should be), and it may no longer sound so good with those preamp tubes.
     
  20. Jethro Rocker

    Jethro Rocker Well-Known Member

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    My TSL was suggested at 90 and it was really hot. I have it set around 84. Too much lower and it loses that liquid tone for leads. But then I obviously play a completely different style and tone from OP.
     

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