Magnatone

Discussion in 'Shock Brother's DIY Amps' started by Clintstone, Jun 20, 2021.

  1. Clintstone

    Clintstone Tele-Meister

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    Buddy of mine gave me an old Magnatone, he chopped down the combo and made a head out of it back in the 90's. Its sure not pretty but it might be interesting to tinker with. There have been some sketchy wiring repairs in here, marettes for the 3 wire cord that was added and electrians tape on the power transformer wiring to name a few. It has a huge power transformer so this thing must have been a beast in its day. 20210620_181716.jpg 20210620_181641.jpg
     
  2. davidge1

    davidge1 Friend of Leo's

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    I used to have an amp from the same line. I don't know if it was the actual name of the line, but they're referred to as "suitcase" amps, because of the built in handle on top. Mine was the bass amp, with a single 15" speaker. I played guitar through it. It sounded really good for that thumping Chet Atkins type sound... great for rockabilly type stuff.

    I saw a clip of the Rolling Stones in the studio on youtube once, and Keith Richards was playing through a smaller one.
     
  3. davidge1

    davidge1 Friend of Leo's

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  4. vhilts1

    vhilts1 Tele-Holic

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    Some Maggie’s are sought after and well thought of widely

    Some are thought of as total dogs not worth a 2nd thought

    Do some research before you get too deep.

    The sought after vintage Magnatones I’ve personally played or heard up close were stunning

    As good or better than many legendary amps
     
  5. Wildeman

    Wildeman Tele-Holic

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    Magnatone turned out some great stuff, ive had a few throughout the years. Right now i have three lap steels two G 70s and an 8 string G65 and two amps, a '59 custom 280 and a '63 Pac Amp 213 Troubadour. Magna is easily in the same class as Fender or Gibson imo.
     
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  6. Clintstone

    Clintstone Tele-Meister

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    My friend had mentioned that he used to get shocks from this amp, this power cord might have something to do with it. It's that crappy wire that won't take solder and the ground wire was just loosely shoved under a self tapping screw ( I think this is actually a block heater cord off an old car) 20210621_082037.jpg
     
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  7. Clintstone

    Clintstone Tele-Meister

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    And of course, mismatched power tubes 20210621_190307.jpg
     
  8. Clintstone

    Clintstone Tele-Meister

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    So I pulled what tubes were left and plugged in my new properly grounded cord. I have 330V out of the power transformer which seems pretty typical. The DC voltages were a little higher than the schematic said but that is normal with no tubes installed, correct? The only tube I don't have is a 12DW7 which seems like an oddball tube. I will order one of those and then see what kind of voltages I get with preamp tubes installed.
     
  9. Clintstone

    Clintstone Tele-Meister

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    So after some more digging I'm wondering if I should just gut this chassis and start fresh. This chassis is huge, 28" x 6" with 6 nine pin sockets, 2 octal sockets, 15 pots and six 1/4" jacks. I'm thinking since the faceplate is destroyed and I am missing some of the reverb circuit I might as well build my own 2 channel amp with 2 very different channels. Like chanel 1 be a Princeton like clean channel and channel 2 be like an SLO type high gain channel. Am I crazy for thinking this would work.
     
  10. NTC

    NTC Tele-Holic

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    This doesn't look like it has the coveted vibrato circuit, but if you have any long, tubular, but otherwise unknown parts on the board, they nay be the special varistors that make Magnatone vibrato so unique. Did you find an original schematic?
     
  11. Clintstone

    Clintstone Tele-Meister

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    Yes NTC I did manage to track down a schematic and I cannot find any special varistors, I believe you are correct in saying that I do not have the cool vibrato circuit. I dug though my box of startup tubes and found enough to test out the clean channel, there is nothing spectacular about the sound at this point. As one would expect the pots are scratchy, but it does make sound. After I shut it down I checked for voltage on the filter caps, after 30 seconds they had bled down to 26V after 1 minute they were down to 3V. Is this an indicator of bad caps or am I just being paranoid.
     
  12. Clintstone

    Clintstone Tele-Meister

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    I am trying to figure out what is going on with this power supply. The schematic which I will post below shows 4 diodes for the rectifier and one more for the power tube bias. All of my previous amp builds use tube rectifiers so this solid state should be simple. Why am I counting 7 diodes when the schematic only shows 5? Screenshot_20210626-161601_Google.jpg 20210626_161125.jpg
     
  13. Nickfl

    Nickfl Friend of Leo's

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    Totally normal, there are circumstances were filter caps will hold a high voltage charge after the amp is powered down but 99% of the time it is not the case.
     
  14. bebopbrain

    bebopbrain TDPRI Member

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    Each pair of black 1N400x diodes is a replacement for a single original diode (presumably the kind with the blue cathode stripe). You should be good.

    The upper terminal strip is, from left to right:
    • 100uF/50V (blue) bias cap connection to bias diode and 22K bias resistor
    • secondary winding connection to rectifier diode
    • ground, secondary center taps
    • B+ about 400VDC
    • secondary winding connection to (replacement) rectifier diode and 56K dimmer resistor
     
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  15. bebopbrain

    bebopbrain TDPRI Member

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    Go for it. But why not hear the amp's own sound first?
    • Install a 12AX7 in V1
    • Remove V2, V3, V4, V5
    • Install a 12AU7 in V6 (a reasonable substitution under the circumstances)
    • Install your unmatched power tubes
    • Plug into the normal channel and play
    If you like that sound, you have 4 tubes left to build your SLO preamp.
     
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  16. schmee

    schmee Doctor of Teleocity Ad Free Member

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    Worth $600 and up in a combo...
     
  17. schmee

    schmee Doctor of Teleocity Ad Free Member

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    I wouldnt, they are fairly coveted by some... what's wrong with the faceplate? looks pretty good...
     
  18. Mongo Park

    Mongo Park Tele-Afflicted

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    I would not build it into something else. Fix it and to a level you can judge the sound/tone and if you don’t want it pass it on. Even a discount resale would buy you some parts for another build. Most filter caps charge continue to run the tubes after shutdown until the tube heaters dissipate and the tubes stop running.
     
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  19. Clintstone

    Clintstone Tele-Meister

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    I think I am going to take some of the advice that has been offered here and order some proper tubes to try and hear what this thing should actually sound like. Regardless of what I build it into I think it should be a combo with a pair of 12's. If I were to buy a reverb tank what should I be looking for, I have never built a spring reverb amp and am kinda clueless about them.
     
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  20. Clintstone

    Clintstone Tele-Meister

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    here is a clip of the reverb circuit, am I correct in assuming the impedance of the reverb transformer is 8 ohm
    magnatone reverb schematic.png
     
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