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Marshall Lead 18 Mini Stack Redux (5 stage pre/MB Driver/EL84/Vibrato/kitchen sink)

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  • Marshall Lead 18 Mini Stack Redux (5 stage pre/MB Driver/EL84/Vibrato/kitchen sink)

    Ever have an amp who's clothes didn't seem to fit right? Remember those cool Marshall Mini Stacks? That's a identity crisis amp- it's all dressed up in it's three piece (head, cab, cab!) but sounding like it does- like the teenage fry cook from the simpsons- it's not going out, hell, it can't even get a call back.

    Which is why you can pick them up for about 125 bucks if you lean on the pawn guy.

    I thought, first, that this amp should have refined tone, a sort of sheep in wolf's clothing. SO, I built a dumble pre, and rewired a champ as a SET power amp. The head housed the pre and the slant cab the power amp. It was cool enough, but didn't have sufficient mojo to make onlookers "dumbled." It was also the first amp I've even been turned down to loan out.

    The next version, i put a vox/ early marshall pre in it, same power amp. Better, but didn't fit it's clothes, at all. That thing looks like a jcm800.

    So, I hooked up one more stage and had me a SET 800. Still Lame! So, I put a ltp driver and a power amp with cathode biased el84s in the box. I pulled the "champ", re-converted it and sold it! The push pull really woke the amp up. It was finally getting somewhere. This was something that would raise eyebrows in the local bar. It has wayyy too large of a power xfrmr and a tiny Hammond 125 10w OT.

    Around that time, I was building another amp for a guy and I started thinking about things like SLOs, x88s, Caswell 39s and such. Any guesses where this is heading? For those keeping score, I've now got 6 tubes, two transformers, etc in the 8"x12" thing... and here's the sticky part:

    I never had any plan for any of this at all. It's stuff everywhere. It's like a computer there's so many cards and boards and wires and OY VEH! Not satisfied, I put on a variable line out, a fan, a load resistor, the cerrem mod (Melted the power tubes in 2 minutes) oh and, of course, fixed bias- to accommodate the solid state bias vary tremolo, because I didn't have enough shit in there and I like trem on high gain- odd but sounds ILLLLL. The grounding is mostly star, but, hey, there's a free ground here and there drilled into the chassis. Strangely enough, the build makes almost no noise whatsoever. AC filaments, not lifted, which they should be, by like 50v for the cathode follower to be healthy, but marshall didn't either. I don't like messy builds because they're hard to work on, frequently unreliable and oscillate. This one is lucky and slow to work on, i'll never do this again!

    So?
    IT RIPS. IT DRINKS YOUR MILKSHAKE.

    Click image for larger version

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    Top View- Not proud of the way it looks.

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    Tube Side- back tubes are power, mid tubes are pre and EQ driver, front tube is middle stage (#39), vertical board is the driver, who's tube is hiding in the back there.

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    Front- Input, Gain (pull bright), Treble (pull v1b bias shift), mid, #39 switch, bass, vibrato switch, Master, footswitch jack (currently not connected), STBY, Mains Fuse, Main Power

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    Back, In box. Visible: Load Resistor, Fan, VIB RATE and INT, Line out LVL, Line out 1/4" + RCA, Cerrem switch (disconnected. Evil, evil switch.)

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    Marsha, Marsha, Marsha

    The bottom cab already has an EV12L. The top is probably getting a greenback or an EVH reissue greenback? dunno. Why does the bottom cab have 200w worth of speaker? Because the last part of the project is a 180w MOSFET Power Amplifier. Yah: I want to power of a Major for my Mini! That should be done sometime next month.

    I know there's another like this out there, a tubed up mini, but I've never seen pics. If anybody knows where to view that amp, that would be cool.

    I'll post some clips monday when I can get some time to turn it up. Thanks for reading!
    Attached Files

  • #2
    wow that's an impressive rats nest of wires! Can't wait to hear the clips!

    were exactly is the 180w mosfet power amp going in the circuit? And its power supply?

    maybe a bigger chassis is in order!

    Comment


    • #3
      Why thank you! It staggers me that it even functions- ie, doesn't oscillate- let alone does so well and quietly!

      The power amp is going after the speaker / load resistor. It's a "reamp" setup, like the 80s all over again, Leather trousers, codpieces and all. It will be either hanging off the back of the bottom cab or inside it. For now I'll run two channels on my ADCOM GFA-2535 bridged, since Marsha might be going to work in the next few weeks, before I get the time to build the mosfet section. It's about 200w, couldn't be cleaner or stiffer, and has another pair of channels for, uhh, stuff.

      There's no space left in the head box, no space I'd call appreciable. I'm already force cooling it! I've got a little corner over by the power switch (which, with the fuse and stby could go to the back) but that's reserved for the power light, not present, and a 5v rectifier tap ---> "rectifier"----> lm7805 circuit for vactrols, which will eventually footswitch to pull out the caswell clipper and probably turn on a clean channel (I have a triode left, which keeps me up at night) but thats, err, not a huge priority here. It doesn't exactly clean up like your (lame) uncles (lame late, feedback strapped) bassman with the volume knob, but I digress. I have a DR for nice cleans if need be- it's probably less work to haul that around then try to get any clean headroom out of this amp, anyway.

      To quote a chuck H that isn't on this board, i'll get a larger chassis when this one is torn from my cold dead hand!

      Comment


      • #4
        I did something similar a while back. I picked up a Lead 100 Mosfet halfstack for $100. I gutted the head and put an 18 watt single channel 18 watt Marshall clone in it with a Voxish preamp. I love it with that matching red 1965A cab, but like it even more with a 1960A (more low end and perceptive volume). I sat in with a band a week or so ago and used one of the guitarist's smallish Peavey tube heads through one of those mini cabs. It didn't sound half bad really. I would buy a mini stack all day long for $125 if it has 2 EL84s, 3 12AX7s (or more) and a PT and OT. You seem to have gone through a lot of trouble. I would have just gutted it and mounted a turret board.

        Comment


        • #5
          The main issue lies in the inverted nature of the chassis- unlike a normal marshall, its like a steel boat, so there was no "x axis" if you will to mount the sockets through- only the power tubes are through socket mounted, on a piece of 1/8 garolite. The rest are surface mount sockets meant for pcb use that are just horrid to use. The construction is point to point on a board to those sockets, the whole thing is inside out. It's also been built and rebuilt 3 or four times, and it could use a cleanup from that "construction site" kind of work.

          the cabs sound small and boxy, even the bottom 12l with a lot of power. The top cab is in my iso cab right now, and the speaker is kinda meh. I kinda wanna put in a greenback, I think that'll sound nice... I also didn't put the feedback circuit in and, when the power amp gets up to power, the amp darkens to my ten-buck ears, so... I think it's fair enough to give it another sesh with that in there and see where I get.

          Comment


          • #6
            Chassis are cheap. Even cheaper if you make one yourself. If you have the verticle clearance of course.

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