Ampeg Gemini G12 Trem works but only on afterbeat.

[Queen*Son]

Finally got another '66 Gemini 1 after my first one got stolen a couple years back. I got it for a good price and knew some of the stuff done to it.

2 10" alnicos which connect via TRS to either a 4 ohm output or 8ohm output, and some kind of toggle switch between them. foot switch wired with a trs (not sure why but it's clean) Has the 3 amperex bugle boys as well. Overall pretty clean, a couple tears in the blue diamond but super shiny faceplate

Had him demo it and wow, was it just like I remembered. I only had him go right to afterbeat, which worked, but not as strong as I remembered. When I got it home I noticed the trem was weak sounding, it's there, but not in your face. It's a little more noticeable with after-beat switched over. Speed and intensity both work, but it's just not full sounding and the lower the speed the less noticeable the tremolo. I don't think it effects the volume or tone either so I'm curious what you guys might think?

TIA

[Jon Snell]

4Meg pots are hard to come by now. Has anyone changer the Intensity pot for the wrong value?

[Queen*Son]

I'm glad this is what you first thought of as this was what I was thinking as well. I haven't opened it up yet so I'm not positive, would that effect the loudness of the tremolo? (that's probably the wrong terminology)

I did a quick Google search and did find a 4meg pot that weren't switched and heard of guys taking the switch (which clearly is good on this pot) and putting it into a new 4meg pot? Is there a specific wattage 4meg pot I should be looking for?

I see a Clarostat 4meg 2watt panel mount pot on amazon 1left for $15, if thats it I'll grab it and give it a shot..

[Jon Snell]

The original pot was 1/4 Watt so anything higher or the same wattage is fine.
To test it, (the tremelo depth) remove one wire from the pot and place a 4.7 or 3.9M resistor in place of the pot. That will demonstrate the maximum depth. If it is not deep enough with the resistor in circuit, check the oscillator for amplitude.

[Queen*Son]

Thanks for the tip. Wondering if when I pop the amp open, if it were a 4meg pot then maybe it isn't within value? Not sure if they wear down like that.

I need to get atleast a couple of hours of sleep but I appreciate you coming and blessing my first post with some solid advice.

Matt

[Queen*Son]

After digging into the amp today it looks like the intensity pot may not be original as it is a 3m pot but seems to be from the same manufacturer as the rest. Could that difference really effect that much of the trem coming through? I have a tm1 module on the way but seems I may have to find a 4m pot.

[Queen*Son]

Looking at the schematic, the intensity pot is 3m, speed is .5m and treble is 4m.

[LowHeadRoom]

I realize this thread is old, but thought I could contribute an answer if anyone stumbles upon this thread via Google as I did.

I changed this resistor from a value of 1 Meg to 247K and my intensity is perfect. Any lower than 247K and it will start acting very strange (the bulb in the roach will intermittently come on and won't turn off). So 247K is the magic number it seens.

Here's a picture of the schematic:


This will get your trem sounding like a Fender Trem.. However, the afterbeat effect will no longer function. The switch will simply cause your roach bulb to be on all of the time. I believe the parallel resistance of the 247k resistor and the 22k resistor does not equate to enough to allow the trem to function properly.

For me, this does not matter. I'd rather have a great sounding adjustable tremolo than an "after-beat" function which is pretty much just the signal passing through a .2 capacitor to make a slight "click click click".

Hope this helps someone in the future. If you know how to get the "after-beat" working again, please let me know! Thank you.