Need help reading schematic

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Leonc, Feb 2, 2006.


  1. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

    Messages:
    16,880
    Joined:
    Jan 4, 2002
    Location:
    Upstairs, L.A.
    I recently acquired an old Ampeg GV22. The amp has two channels. It also has reverb, tremolo AND vibrato. There is a switch that enables you to select which you want--tremolo or vibrato (i.e., only part of the trem/vibrato circuit can be active at any given time). A 2 button footswitch is provided - one for reverb the other for the trem/vibrato circuit.

    The reverb wasn't working when I got it, but I've subsequently got it working (with an assist from Doug Roccaforte)...I think.

    Here's Joe Piazza's version of the schematic.

    Based on this schematic, should the reverb work on both channels? I'm thinking, no...it only works on channel 1 (this seems weird...but then, it's a weird amp!) It also looks like the pre-amp out may only be for channel 2.

    Now...I'm also thinking that it might be reasonable to expect a bit more gain from Channel 1 as it's going through both the reverb and the trem/vibrato circuit.

    Of course, if I'm actualy correct here (not a great bet), you must stop thinking of me as a complete technical lame-o and instead can begin thinking of me as a partial technical lame-o.
    :BEER

    Note that in the schematic, Channel 2 is on top with Channel 1 below.
     
  2. fullerplast

    fullerplast Senior Member

    Messages:
    6,793
    Joined:
    May 5, 2003
    Looks to me like you are correct about the reverb/trem only being on channel one, but wrong about the preamp out. That is for either/both channels. So I guess you are halfway to being a partial technical lame-o......:D
     
  3. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

    Messages:
    16,880
    Joined:
    Jan 4, 2002
    Location:
    Upstairs, L.A.
    Awesome...I'm feeling very proud right now!!! :)
     
  4. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

    Messages:
    16,880
    Joined:
    Jan 4, 2002
    Location:
    Upstairs, L.A.
    Hey is that because of the signal coming out of the end of the reverb circuit with the 150k resistor heading up to the pre-amp out? That would imply that you get the reverb in the pre-amp out of channel 1, yes?
     
  5. fullerplast

    fullerplast Senior Member

    Messages:
    6,793
    Joined:
    May 5, 2003
    Yep, that's it.....and that is also the input to the phase inverter, which both channels go to.
     
  6. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

    Messages:
    16,880
    Joined:
    Jan 4, 2002
    Location:
    Upstairs, L.A.
    Okay so the 7199 is the phase inverter. See, this is why I'm still only halfway to being a partial technical lame-o... I was thinking it must be, because it appeared to be setting between the power section and the pre-amp.

    How about what I was theorizing about the gain in channel 1 vs. channel 2? Is that close to the mark (because emperically, channel 1 is definitely the money channel on this amp)?
     
  7. fullerplast

    fullerplast Senior Member

    Messages:
    6,793
    Joined:
    May 5, 2003
    Yes to that also...you're almost a full lame-o at this point!:)

    You have two stages of the 6CG7 driver tube and one stage of the 12AX7 recovery tube. Not all that is intended for gain, but the result is likely a hotter signal coming out of that channel. You'd have to go through the stages to figure out exactly how much gain.

    I really like the tone stack on most Ampegs BTW. Cool amps.:AOK
     
  8. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

    Messages:
    16,880
    Joined:
    Jan 4, 2002
    Location:
    Upstairs, L.A.
    Wow. Learning is fun.

    When you refer to a tube's stages (as in the two stages of the 6CG7), it's because the tube has multiple sets of electrodes (like the 6CG7 is a dual triode, right?)? And it looks like the output from pin 1 is fed as input into pin 7, right?

    By recovery, I take it that we lose some electrons by going through the reverb tank, yes? so we're building replenishing our supply by going through 1/2 of V7?
     
  9. fullerplast

    fullerplast Senior Member

    Messages:
    6,793
    Joined:
    May 5, 2003
    Careful, you're gonna start making Fred nervous......:D
     

Share This Page