Replacement Tremolo Optocoupler for a Ampeg G15 Gemini II

[5thumbs]

Hi Gang,
I have a 60's vintage Ampeg Gemini II G15 that the tremolo went out on. The original optocoupler is still in the circuit and I want to change it with a new one. This thing is a plastic box about the size of a reverb transformer (just a little smaller actually). Can I replace this with a Fender LDR style? The only schematic for this amp that I can find is so fuzzy I can't make out any values going in or out of the unit which is labeled: TM-1 (part number?). Thanks for any light you can shed on this for me.

Tim

[52 Bill]

I've tried using the Fender replacements and have had no luck in getting them to work well enough to call the amp fixed.

Fliptops carries a TM-1 replacement, which is expensive, but works well.

Why do you need to replace the one that you have?

[5thumbs]

The tremolo is very weak and hardly has any range from off to full crank. It always seems to be the module on the old blackface Fender's that have gotten "weak" and when I replace them they sound great. Do you think it might be something else on this amp? I swapped the driver tube with no positive results, all resistors and caps in circuit visually look fine and no cold solder joints from probing with a chopstick. If you have knowledge of what I should check, I would greatly appreciate it! I just know enough to be dangerous ;-)

[52 Bill]

You may be right, and the optoisolator needs to be replaced. But I'd make that the last resort in the repair.

Ampeg used a very different approach to trem than Fender did, and I've never heard an Ampeg that got as deep as a Fender. Instead of reducing the audio signal by sending part of it to ground, the Ampeg design increases the signal by diverting it around a high value resistor.

Visual inspection of parts is good, but it will not tell you if something has gone off value. If you haven't done it already, check those parts with a meter.

[5thumbs]

Thanks Bill,
You're right, I need to meter all the values first. I will do that today.

Tim

[harojs]

Tim,

Did you ever determine what component needed replacing for your weak Gemini II tremolo ?

-John
pelkie123@msn.com

[Queen*Son]

Any updates?