1992LEM vs 1973 Super Bass

Discussion in 'Marshall Amps' started by Clammy, Dec 20, 2013.

  1. MartyStrat54

    MartyStrat54 Well-Known Member

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    dreyn77-Please stop posting your nonsense. You are disrupting this thread.
     
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  2. MartyStrat54

    MartyStrat54 Well-Known Member

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    Clammy, I like the Super Bass. It seems to be at least 3dB louder than the LEM.

    It would be interesting to know what the plate voltage is on these amps.

    You might want to try a set of TAD EL34's in the LEM. They are high transconductance tubes and they should give you a little more grunt.
     
  3. Clammy

    Clammy Well-Known Member

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    I was REALLY surprised by the volume difference. The LEM was ear-bleedingly loud... the 73 was mind-numbingly loud, hahaha!!

    I'm also curious about the plate voltage on the LEM head. Visually, the power transformer looks BEEFY, but the 73 SB puts near 500v on the plates, and I somehow doubt that the LEM is in that range (pure speculation on my part, and I may be pleasantly surprised when I actually measure it, which I plan on doing in the near future.). I'm also pretty positive that it's biased ice cold. The amp is brand new, so it would have the factory bias setting, which I've read is cold, to preserve power tube life.

    I have a pretty new set of JJ 6CA7s, that I'm going to try in there, too. It already has SEDs (which are my favourite CP EL-34s), and I bet there are just a few hours on those. And, I'll also try the xf2s in there. Lots of messing around to come.

    TADs are just rebranded CP tubes, right?

    Cheers!
    :hbang::hbang::hbang:
     
  4. damienbeale

    damienbeale Well-Known Member

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    It's unlikely (completely dependant on your wall voltage of course) that the LEM will be over the 465-475V range, simply because current production tubes can't handle the screen voltages (although Winged C's have a good stab, and the current Chinese EL34B's seem to handle it with ease, ALTHOUGH they are not a true EL34 design, underneath the clothes). Marshall quite deliberately keep the voltages lowered since those original amps, and rightly so. Most people just don't have the glass to make such amps reliable roadworthy machines.

    This really is a large part of the reason why vintage amps get a bad rep for reliability. It's not the amps fault, but the fault of tube production since the 80's. Old Mullards take this punishment in their stride, which is pretty much all that were fitted back then, since they were absolutely EVERYWHERE in England.

    And the TAD's are a Chinese tube, so they should be pretty damned rugged in comparison to the likes of JJ and Reflektor (Sovtek, EH, Tung-Sol, Mullard reissue, etc). I'm not convinced that rebrand is the right word these days, since the Chinese plants seem to do an awful lot of special builds to order, of which the TAD could well be one of. I'm sure Marty can fill in the gaps.
     
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  5. dreyn77

    dreyn77 Well-Known Member

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    Mod edit
     
    Last edited by a moderator: Dec 23, 2013
  6. bulldozer1984

    bulldozer1984 Everybody's Favorite Member VIP Member

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    seriously shut the **** up. You have no ****ing clue what you are talking about. I honestly cant believe you are still here. Its a major failure on the moderators behalf.
     
    Last edited by a moderator: Dec 23, 2013
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  7. Clammy

    Clammy Well-Known Member

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    Stay out of my thread.
     
  8. MartyStrat54

    MartyStrat54 Well-Known Member

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    The TAD EL34B STR's are German designed tubes made by Shuguang. A while back I verified that the TAD is indeed an exclusive tube. It looks like a regular Shuguang, but it has superior internal components, including gold plated screens. It has the same electrical specifications as a NOS EL34. They are reasonably priced.
     
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  9. Adwex

    Adwex New Member

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    I'm not sure.
    I listened to the clips before I read your full post, so I was gonna cry "foul" on the A/B test, because I thought for sure you changed some settings or mic position or something, the vintage SB was just way louder. I can't believe how much louder it is, WTF?!?!
     
  10. MartyStrat54

    MartyStrat54 Well-Known Member

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    Has to be how the preamp circuit is configured. It's obvious that the SB is getting a lot more gain out of the preamp and therefore driving the power tubes harder with the same knob settings.
     
  11. Clammy

    Clammy Well-Known Member

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    Ah, ok. I just thought they were rebrander. Can those tubes take 500v plate voltages?

    Cheers!
    :hbang::hbang::hbang:
     
  12. Clammy

    Clammy Well-Known Member

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    Man, you should have been standing in the room with me. First, the LEM head was loud enough to peel paint. Then the 73 was just.... insane!! The sound pressure was enough to blow the bulb in the lamp that was nearby, hahaha!! And that's with the bass control set to zero! ;) I wish I would have had a dB meter. I would really like to see what those amps clock in at. And the volume was at 8. There was a slight, but noticeable increase in volume when I dimed them (and of course, I HAD to do that! :D ).

    Cheers!
    :hbang::hbang::hbang:
     
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  13. Clammy

    Clammy Well-Known Member

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    Supposedly, the circuit is a copy of Lemmy's "hotrodded" 76 Super Bass. Thing is, I've never been able to find out exactly WHAT was "hotrodded", but I would imagine, the preamp is goosed in the LEM head. The 73 is bone stock. A few differences that I think may have to do with it:
    1. The power tubes.
    2. The plate voltage (I'm almost positive that the LEM is nowhere near the 500ish v the '73 puts out).
    3. The NFB tap and resistor value (I don't know the taps or values for either).

    Cheers!
    :hbang::hbang::hbang:
     
  14. damienbeale

    damienbeale Well-Known Member

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    If they're anything like the other Shuguang B's, then they'll breeze it. Of course it's not the plate voltage that's the issue anyway, it's the screen voltage which will probably only be around 10-15V lower.
     
  15. Clammy

    Clammy Well-Known Member

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    Yeah, that's true. Since they're single B+ rail design, the plates and screens see close to the same voltage, so I just use the plate v number, heheh... my VBAs are dual rail design, so the plates are getting something in the 700vdc range, while the screens are about half that (IIRC).

    Cheers!
    :hbang::hbang::hbang:
     
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  16. washapdude

    washapdude New Member

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    Any updates on if the bias or anything was affecting the volume of the LEM? I just purchased one and have to wait two weeks to get it. I understand the thread is two years old, but an update would be great! Thanks!!

    :hbang::hbang::shred::shred:
     
  17. Clammy

    Clammy Well-Known Member

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    A long time ago, I pulled the chassis with the intent of setting the bias the way I normally do, but I found 2 trim pots on the board. After much searching on the 'Net, I have been unsuccessful in finding the bias procedure for the amp, so she sits as she was the day I posted this thread.

    If anyone out there knows the bias procedure for this amp, please let me know!

    Cheers!
    :hbang::hbang::hbang:
     
  18. neikeel

    neikeel Well-Known Member

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    I think that one will be the bias pot and the other will be the heater trimmer (to give symetrical voltage either side of the heater centre tap to minimise heater hum).
    Post a clear pic of that end of the board and someone/we will talk you through it:cool:

    Here is a board with one, is yours like this?

    [​IMG]
     
  19. Clammy

    Clammy Well-Known Member

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    Yep, same board, slightly different components. :D So which trimmer is the bias pot, and which one is the balance pot? I know how to set bias. But have no idea about the procedure for the balancer.

    Here's the 1992LEM's board. I took this when I pulled the chassis last year:

    [​IMG]

    Cheers!
    :hbang::hbang::hbang:
     
  20. MeshAudio

    MeshAudio New Member

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    VR1 is the Bias pot and VR2 is the Hum Balance pot.
     

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