weak reverb, Gemini VI, schematics included

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by briangibson, Sep 14, 2006.

  1. briangibson

    briangibson Member

    Messages:
    44
    Joined:
    Jan 19, 2006
    So I just got an Ampeg Gem VI off ebay on the cheap but it needs a little work. the reverb is rather weak compared to my Gemini GV-22. I tried swapping the 6CG7/12AX7 tubes with no luck. next guess is either a bad reverb tank or some caps in there i should swap out, any particular bad boys in the schem I should take a gander at?

    [​IMG]

    thanks!
    brian
     
  2. briangibson

    briangibson Member

    Messages:
    44
    Joined:
    Jan 19, 2006
    OTM: i actually thought about that, i think I'm gonna give that a shot later today to isolate the issue more thoroughly.

    One question for ya or anyone else who stumbles upon this thread: I'm going to also be replacing the LED as the amp came with none whatsoever currently- is it the triangle on the schematic connected to the negative end of the bias cap, between the 56k resistor? Also going to be adding a 3 prong power cord- anything i should note to change under these directions http://www.theguitarfiles.com/guitarfile644.html for an Ampeg that I might overlook? Obviously I'm just getting started with amp tinkering.
     
  3. donnyjaguar

    donnyjaguar Member

    Messages:
    4,244
    Joined:
    Nov 4, 2005
    Location:
    Canada
    Try moving the Reverb "send" point from the rotor (wiper) of the Treble pot' to the 20n (low side) coming of V4a. Now replace the 270k resistor with 560k and you should have more reverb than you can stand.

    Whether this will blow the input coil to the reverb tank remains to be learned. :)

    You could also replace the 47k resistor that goes from V5a(2) to ground with 560k for a milder increase in reverb drive.

    I just noticed that the plate resistor on the pentode portion of the 7199 tube is quite low. You can replace this with something much higher (like 220k) and get bags more drive into the output stage. :)

    Say, you don't need that tremolo do you? You could add this additional stage to the amplifier and get some "boogie" action going - and that 500k control would make a fine master volume. ;)

    DJ
     
  4. briangibson

    briangibson Member

    Messages:
    44
    Joined:
    Jan 19, 2006
    very interesting ideas! hmm, i'll try replacing the verb tank first and then if that doesnt do it i might try some of those mods. i do like the trem though- it sounds even better than my GV-22's tremolo, and the gv-22 has afterbeat/vibrato options too. will that drive mod put undue stress on the power tubes?
    Brian
     
  5. briangibson

    briangibson Member

    Messages:
    44
    Joined:
    Jan 19, 2006
    replacing the verb tank didn't fix it, so my reverb issue is something else in the circuit. also i should mention adding the LED lamp added some audible difference in buzz, is there a good way around that?

    b
     

Share This Page