80's Solid State Combo Tube Conversions

Discussion in 'Marshall Amps' started by bigragu63, Sep 3, 2019.

  1. bigragu63

    bigragu63 Member

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    By request, I'm starting this thread dedicated to my ss combo conversions.

    Let me start by saying that I don't claim to be an amp guru, or that my ideas and designs are anything that hasn't already been done before. Or, even any good.

    I'm just an old rocker with a lifetime of experience with some practical and useful skills I can apply to amp building.

    To avoid taking my vintage Marshall 4010 to gigs, and preserve its condition and value, I bought an old Model 5210 amp that was listed as "not working" on ebay for its cab and chassis. I gutted the chassis, and special ordered a JCM800 build-it-yourself kit online that included all the parts, unassembled, no chassis. I figured I can drill holes, not sweat putting a ding in the tolex or grill colth, and mod, un-mod, and re-mod with no limits or fear of destroying any vintage value.

    I drilled and punched all the necessary holes to mount everything in the 5210 chassis, except for whatever holes already existed for pots and jacks.

    This first amp is named "Franky", which was also my dad's name (RIP Dad)
    Unfortunately, I can't find the pics documenting the progress of the build, but my later two builds, Franky Jr., and Lead 20 are well documented. They are also using old ss combo donor chassis's. So, some of Franky's pics are from Franky Jr's cab and chassis to show before and after.

    Franky looked like this before I dug in:
    20150207_151240.jpg
    No guts
    20150208_154126.jpg
    Making it holy
    20150208_221023.jpg
    Fast forward...
    IMG00063.jpg
    Now with guts... Done!
    20141101_152345.jpg
    As we see here, I decided to make it a 4 hole Plexi instead of JCM800 with a couple more input jacks, and a few circuit tweaks. Hey, why not!
    20141101_150456.jpg
    Here we see the pentode/triode swith above the voltage and impedance selectors, as well as speaker and effects loop jacks
    20141101_152129.jpg
    So, Franky is a basic 4 hole Plexi with a JCM800 style pre phase inverter master volume, a pull bright switch on the preamp gain pot, an effects loop, a PPIMV, and a half power switch.

    Franky Jr is way more modded, and has classic tone iron, Sozo caps, tinned teflon wire, F&T filter caps, all the features Franky got, plus externally adjustable bias, 3 way switch for multiple negative feedback resistor values, and a multi voltage transformer using a 3 position standby switch to switch from standby to either high or normal voltage. Thinking about swapping the high voltage to the 3rd, low voltage option to brown the sound some and see what that sounds like.

    The most crazy mod I did on Franky Jr was to add a 4th preamp tube and a switch to reconfigure the bright channel to be either stock Plexi or JCM800. And, you can still jump the 800 channel to the normal channel for even more versatility.

    Here's some Franky Jr gut shots. Check out the labyrinth of shielded wire on the JCM800 mod switch.
    20190903_211059.jpg
    20190903_211136.jpg
    20190903_212244.jpg
    There you have it. I'll follow up with details on the Franky Jr. and Lead 20 builds when I can, along with some sound clips.

    Thanks for looking!
     
    Last edited: Sep 3, 2019
  2. guzzis3

    guzzis3 Member

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    Really sensible. Buying an unloved SS amp to "recycle" solves quite a few problems. Well done.
     
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  3. Jethro Rocker

    Jethro Rocker Well-Known Member

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    Holy crap. I don't know what to say. You are indeed an amp guru IMO. I love the metal toggle and square LED on the front as per the Canadian amps like my original Jubilee.
    Well done and they sound like very useful mods.
     
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  4. Cadorman

    Cadorman Well-Known Member Premium Member

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    Pretty cool.
     
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  5. scozz

    scozz Well-Known Member

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    Very nice,... I imagine doing something like that is quite rewarding!
     
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  6. Drinkingdeath01

    Drinkingdeath01 Well-Known Member

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    This is super cool and thank you for sharing it with us. I would love to have the time and patience to try this at home but a man's got to know his limitations. I've been cursed in soldering and my ADD would immediately turn a project like this into a garage fire in record time.

    Something about a small tube modded Marshall combo seems killer to me. Rolling up to a gig with a little fire breather that nobody suspects would be something I'd be into.
     
  7. Adieu

    Adieu Well-Known Member

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    Cool

    But please only harvest the dead ones
     
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  8. tce63

    tce63 Well-Known Member

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    COOOL :applause:
     
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  9. Musicmaniac

    Musicmaniac Member

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    Very cool. Thanks for sharing!
     
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  10. Gunner64

    Gunner64 Well-Known Member Premium Member

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    Cool, but does it sound better than a 5210? Those little bastards rip.
     
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  11. Filipe Soares

    Filipe Soares Well-Known Member

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    AMAZING!!!! I'm still getting courage to do something similar without your knowledge and talent!!! my respects man!
     
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  12. DonP

    DonP Active Member

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    I gutted a Gorilla and put in a 2203 pre (using 2 12AX7's) with a 50C5 power tube and a 35W4 rectifier. This was back in 1990. I didn't know any better so I made a circuit board.

    It has some push pull pots, most noticeable is the one to change the tone stack to a bass.
     
  13. anitoli

    anitoli Well-Known Member

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    Awesome.
     
  14. 2203xman

    2203xman Well-Known Member

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    Got a 5210 box that I've been hanging on to for years.I gave the amp and chassis away like a dummy.I just wanted a 1x12 cab at the time.I used the tolex covered back board to fill the space in front,and it fit perfectly.Made quite a nice 1x12.I have been wanting to insert a 1987 or 2204 amp in it for awhile.Wish I had kept the old chassis now.
     
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  15. black knight

    black knight Member

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    Cool stuff! So you have 47k, 100k, and 170k NF resistors on the switch and the switch wired to the 8 ohm tap on the impedance selector? What setting do you prefer? And please correct me if I'm wrong. I'm trying to learn all this stuff. I recently moved the 47K NF resistor from the speaker output jack to the 8 ohm tap on a Metro 1987 build and it flat out woke the amp up. Prior, it sounded constricted now quite lively and looser. Plus the Lar-Mar PPIMV now is useable.

    Again, great stuff man. Looking forward to hearing them.
     
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  16. bigragu63

    bigragu63 Member

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    Thanks for all the likes, positive feedback and kind words guys! I am truly humbled.
     
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  17. bigragu63

    bigragu63 Member

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    I don't actually know the answer to that one. Never had the opportunity to hear one that worked. The ones I got for these builds were either totally dead, or just about dead, and didn't make any good sound.
     
  18. bigragu63

    bigragu63 Member

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    Thanks Man!

    My thinking on using the 8 ohm tap was to follow the Plexi wiring scheme as opposed to the JCM800 coming off the 4 ohm tap since I wasn't after maximum possible distortion, but more of a classic sound and amp stability.

    So I went with the two typical Plexi and JCM800 NF resistor values of 47K and 100K to be able to switch between them, and since the switch had 3 positions, and 100K is nearly twice the resistance of 47K, I doubled it again using a 220K.

    I like the 47K most of the time, but notch it up to the 100K for a little more bite sometimes. The amp starts getting screachy with ugly feedback on the 220K if I have the amp really cranked. Your question made me think maybe a 150K would be more usable as the 3rd value.

    Haven't tried it on the 4 ohm tap yet. But now I'm gonna have to!
     
    Last edited: Sep 4, 2019

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