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Mesa Nomad and changing that parallel V1

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  • Mesa Nomad and changing that parallel V1

    The Mesa Nomad runs V1a and b in parallel. There's a jumper wire connecting pins 7 and 2. Could I mod this to a more traditional configuration for more gain?
    Another thread on the Marshall forum (here) talked about jumpering pins 8 and 3 (didn't do much at all), or adding a cathode cap and resistor to ground from that floating pin 8. Would I need to cut that jumper from pins 7 and 2?

    Click image for larger version

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  • #2
    Check it out. In Nomad 55 I've seen were linked together anodes and grids, but not the cathodes.
    The value of anode and cathode resistors (150K and 1K5) are not the most usual for a parallel configuration.

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    • #3
      The schematics posted are typical Mesa with deliberate errors.
      Chan 2 - 3 part - there is no path thru' the tube and simply would not work.
      Key here is to see if pins 3 and 8 are connected, that is, are the triodes definitely in parallel.
      If they are in parallel, gain would be much the same as a single stage with 300K anode and 3K cathode - that is, values to screw max gain from the stage. Advantages of the parallel arrangement would be lower output impedance (about 1/2) and slightly better noise performance (by root 2).
      Cheers,
      Ian

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