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Vintage Magnatone MP3 Tube Position Chart

Discussion in 'Amp Tech Center' started by GaryLC, Nov 24, 2020.

  1. GaryLC

    GaryLC TDPRI Member

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    I recently acquired an old Magnatone MP3 amp, and the seller removed all the tubes and packed separately (which I appreciated), but he didn't provide any info as to which sockets they go in. I have the schematic for the amp, but doesn't help me with installing them correctly, just how they tie into the circuit.
    It's obvious where the two power tubes go, but there are 3-12AX7s, 2-12DW7s and one- 12AU7.
    Would any of you be able to provide with a tube layout chart? This isn't something I'm going to guess at!! :)

    Thanks so much!
     
  2. Jon Snell

    Jon Snell Tele-Holic

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    Here is a layout;
    Screenshot 2020-11-24 at 15.11.35.png
     
  3. GaryLC

    GaryLC TDPRI Member

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    Jon, Thanks, I thought that wasn't right, but you are dead on the money, sorry about that!!!!! I had that chart all along, with the schematic, and for some reason thought it was just showing what each of the "V" designations were. I'm a dummy...
    Thanks so much!
     
    Last edited: Nov 24, 2020
  4. GaryLC

    GaryLC TDPRI Member

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    Another tube question.....I got everything installed, and powered her up. Let it sit on standby for a minute or two, then switched to on. After about 10 seconds, started making a strange noise, and I noticed that one of the EL34 tubes was red-plating, glowing like it was about ready to blow. I turned it off, let it cool down, then swapped the EL34s. Turned it on again, the same thing happened to the same tube, but now in the other socket. Should I assume that tube is bad, or is something else going on?
    Frustrated.........
     
  5. Mark the Moose

    Mark the Moose Tele-Afflicted

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    Since it follows the tube I would start with a new set of el34’s.
     
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  6. Jon Snell

    Jon Snell Tele-Holic

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    Check for voltage F first. If not -ve enough, a stronger EL34 will over cook itself.
    Check the -ve bias voltage is correct or enough to lower the dissipation as it shouldn't be anywhere near class A.
    AND remove the death cap and fit a 3 core mains lead for the users safety!
     

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