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The Sovtek amp from hell

Discussion in 'Amp Tech Center' started by Diverted, Mar 3, 2021.

  1. Diverted

    Diverted Tele-Meister

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    This should be fun.

    I helped clean out the workshop of an old time amp tech yesterday. Along the way I picked up this beast Sovtek Mig 100. I'm looking through it and god what a mess. The tech, Guy Claret, had a patent for power scaling in amps and though I don't know hardly anything about his circuits, it looks like this was one of his experiments. The chassis was found in one part of the basement, the cabinet in another. He did all kinds of crazy mods to this amp. Luckily the original boards are intact and as it's not a complicated circuit, I should be able to reverse engineer it back to where it was originally. It will be a fun project. Luckily it looks like the transformers are all good. That was really my only worry. IMG_7461.jpg IMG_7462.JPG IMG_7463.jpg IMG_7464.jpg IMG_7465.jpg IMG_7466.jpg
     
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  2. johnny k

    johnny k Poster Extraordinaire

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    Don't stick your tongue in there.
     
  3. StrangerNY

    StrangerNY Friend of Leo's Gold Supporter

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    I had a MIG 50 for a while. Those are great amps. If you can get it back to original it'll be a tank.

    - D
     
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  4. J. Bonkosky

    J. Bonkosky Tele-Meister Silver Supporter

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    I don’t have a lot of love for that amp in stock form, but yikes! Looks like a mess. Maybe plug it in with a current limiter and see what you get. It might be awesome.
     
  5. _MementoMori_

    _MementoMori_ Tele-Holic

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    The MIGs are big in the doom metal scene. The 50 and the 100.
     
  6. Greg70

    Greg70 Tele-Meister

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    I remember when those were all the rage in the early 90s. Never had one. I may have tried one out at a guitar store at one time.
     
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  7. Wally

    Wally Telefied Ad Free Member

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    4 gain stages prior to the tone stack....should be some gain there. I had experience with the MiG 50 when they first came out.....New Sensor warranties a PT that went down in short order. I was a dealer and did not need that sort of problem, so I did not venture farther with Sovtek amps. The 50 is a lower,powered version of the 100.
     
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  8. Diverted

    Diverted Tele-Meister

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    Too late.
     
  9. Diverted

    Diverted Tele-Meister

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    It's nowhere near being ready to plug in with a current limited. Plus I don't want to blow my isolation transformer :) I won't power it up at all until I at least get the rectifier and bias circuits sorted out and isolated from the rest of the circuit.
     
  10. kbold

    kbold Friend of Leo's

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    Nice combination of PCB and point-to-point wiring. Perhaps the modder was trying to obtain the best of both methods.
     
  11. Ten Over

    Ten Over Tele-Holic

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    MIG 100 and 100U are three gain stages and a cathode follower that drives the tone stack. MIG 100H is four gain stages with the tone stack driven by the plate of the fourth gain stage.

    Sovtek 100 U.gif
     
  12. Ten Over

    Ten Over Tele-Holic

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    MIG 50's are JTM45 style.
    Sovtek MIG 50 Varistors.gif

    Sovtek MIG 50-007.gif
     
  13. Mr. Lumbergh

    Mr. Lumbergh Poster Extraordinaire

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    To be fair, it is easy to mistake that rat's nest of wires for spaghetti.
     
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  14. Wally

    Wally Telefied Ad Free Member

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    Ten Over, I was looking at a schematic from EL34 world that might have been misdrawn. It is different from what you have provided us. I don’t think I am misreading it, but the tone stack in this scheme is not being driven by a cathode but a plate.
    I was expecting to see the cathode follower, but there it is show8ng a plate driven tone stack instead of a cathode follower buffer stage. Apologies for the misdirection....
    https://el34world.com/charts/Schematics/files/Sovtek/Sovtek_mig100h.pdf
     
  15. radiocaster

    radiocaster Poster Extraordinaire

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    They're completely different amps, the MIG50H is the one with the master volume.

    The regular MIG50 has no master volume, but it does have a voltage switch if you remove the back cover. Maybe one of your bright customers had that idea.
     
  16. Wally

    Wally Telefied Ad Free Member

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    I doubt that.....but possibilities abound.
     
  17. radiocaster

    radiocaster Poster Extraordinaire

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    Although I'm not too sure it would fry the transformer, you would be putting 120V through an amp for 220V. The heaters won't work, maybe if you keep it on for very long it might fry something. Not sure.
     
  18. Ten Over

    Ten Over Tele-Holic

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    EL34 World doesn't have the 100U schematic, they only have the 100H schematic. You're not misreading anything, they're just two different amplifiers.
     
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  19. Ten Over

    Ten Over Tele-Holic

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    Here is an original MIG 100 schematic.

    Sovtek MIG 100 Original 2.jpeg
     
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  20. Diverted

    Diverted Tele-Meister

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    Oh, you like spaghetti? This is a Princeton Reverb clone (using an original board with new chassis, transformers pots etc; I never could figure that out) that a friend of mine bought on Craigslist. He brought it to me to fix, as it was.... noisy. I gutted completely and started from scratch. 95EE6933-152B-4652-87FE-61A79C1C1DD6.jpeg
     
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