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Challenger CH18 - Questions from a snooper, not an electronics person :)

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  • Challenger CH18 - Questions from a snooper, not an electronics person :)

    I'll keep this brief! I am a musician and have a curiosity for all things, a lot of these questions will be pretty basic and possibly irritating.

    I have a Challenger CH18 PA that I would like to voice for guitar use. (schematic attached)

    So here are my questions:

    1) Motor and Power Socket: In order to remove the Phono Motor, could I simply disconnect the connections it makes to the input socket (2, 3, 9, and 12) and the other connections (before the point that leads to power pin 10, the .25uF cap, etc) and be done with it?
    -In short, how can i trash this weird 15 pin socket and wire up a 3 prong? And get rid of the phono motor section?

    2) Phase Inverter: For fun, I would like to know what type of PI this is using. I understand that the 6SL7 is given the driving duties here. Long Tail? It looks a little funky, but again i don't really know what I'm talking about . Cathodes are tied, but it looks like the grid on the second half is fed by the first half's plate. ???

    3) Inputs and Cap values: I realize that the phono input has a huge bass boost and is meant for about -20db (also instrument level) and that the microphone input is meant for significantly lower levels (-50db) and is probably voiced for speech 2-5kHz. Would I benefit from abandoning one of these inputs or should I simply lower or raise cap values behind each input to fit guitar bandwith? Could I get away with just replacing the tone stack with something tried and true? Will the mic input just be very overdriven (not a bad thing)?

    4.) Finally, is there a feedback loop of some sort from the tone control to the speaker output (the wire just to the left of the letter "O" in "Output Strip."

    Thank you for any help you can offer up!
    Greatly appreciated
    Attached Files

  • #2


    • #3
      Challenger CH18


      How did your conversion of the CH18 to guitar amp go?

      I also bought a CH18 and would like any info you have.




      • #4
        Tore the circuit out and started from scratch!


        • #5
          Wow! Dual vibrators! Kind of complicated but for AC operation the line goes between the two black wires and the 6.3VAC for the heaters comes from the Black and Green wires. It's a different black wire than the AC line, make sure you have continunity to the green wire.

          The Death cap is the one outlined by a dashed line, it should be removed when a grounded AC plug is installed. A fuse on the AC power should also be installed. Typically 1.5A or 2A slow blow. You might use the Phono Motor Switch hole to mount the fuse holder.

          Got any pictures of this thing?
          WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
          REMEMBER: Everybody knows that smokin' ain't allowed in school !


          • #6
            Looks like this thing is from the days when cars all had 6v batteries. Before 1955 or so. I doubt if you are going to run the thing off of DC. I would gut it and start over.


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