fender twin reverb 68 custom solid state tremolo

[hobiesound]

Hi All,

I have a modern fender reverb here for repair. The tremolo circuit is broken. It's one of the newer rohs compliant versions without an opto-coupler and a solid-state replacement circuit. I already found a couple broken high-voltage transistors on the tremolo assy and a broken pcb fuse in the tremolo power supply. But i don't want to waste time repairing the smd tremolo pcb ( i will if fender won't sell me a replacement). I noticed that in the service manual only the uk and eu versions get the solid-state tremolo. And all the parts are in place for the rc tube oscillator (i can actually hear the crosstalk if i open up the intensity control so it's oscillating). I have a couple old twin chassis's with parts with the opto on it. So i'm thinking i can just remove the solid state tremolo. Rewire the bias power supply wiring and solder in the opto and have a working tremolo. Before i trace all the stuff and commit to this. Has anyone ever done this and are there any gotcha's?

Greetings,

Thomas

 

[hobiesound]

https://www.tdpri.com/attachments/68-custom-twin-reverb-service-manual-pdf.475792/
link to the service manual.

 

[saint gillis]

Hey, I've just had today a Fender Deluxe 68 with the same solid state replacement tremolo circuit.

When the "Intensity" pot is at max, it brings a noticeable amount of white noise to the amp, I don't recall it does so with the opto-cell, does it?

I'm tempted to replace it with an original LDR too...

 

[abbey road d enfer]

Hey, I've just had today a Fender Deluxe 65 with the same solid state replacement tremolo circuit.

When the "Intensity" pot is at max, it brings a noticeable amount of white noise to the amp, I don't recall it does so with the opto-cell, does it?

I'm tempted to replace it with an original LDR too...

You may make the circuit somewhat quieter by replacing the TL072 with an OPA1642 (only SMD so needs an adapter).
However, the noise level is probably governed by the LM13700.

 

[hobiesound]

I noticed i haven't updated my post. In the meantime i fixed the amp.

I pulled an opto-coupler from an old junk silverface chassis and soldered that in. Removed all the solid-state opto circuitry and rerouted some power transformer wiring.
That was all that was needed to fix the tremolo.

Later Fender told me they couldn't sell me the solid-state tremolo pcb assy. So i'm glad i went ahead and modded the amp to non-rohs spec.

It wasn't my amp so i'm not sure if the circuit introduces more noise. I never heard the Rohs tremolo circuit.

Greetings,

Thomas

 

[saint gillis]

Do you still have the amp in your hands?
If so, do you have more noise when you rise the "Intensity" pot with tremolo off ? I guess not

 

[SteveF]

Never ceases to amaze me how some of Leo's original circuits are still preferred over "modern technology". The AB763 circuit will be officially 60 years old next month.