O.k. I am no amp tech. I had weak vibrato on my fender twin. I bought a new optocoupler, put it in, and it sounded a little better. then, I got CRAZY.
I took the old bulb and LDR (light dependent resistor).
First I cut a piece of tinfoil like a little square, 1 cm by 1cm? and then used black electrician's tape and taped it (tin foil, bright side facing bulb) around the outside (away from the LDR) and continued taping it to the LDR. I then used more small pieces of tape and sealed it off from light.
The idea (crazy) was to use the tinfoil piece to reflect light back at the LDR, to improve the effect.
I soldered it back in and:
My Vibrato is strong clear and bright, big improvement, and much better then the new optocoupler. I actually unsoldered it, put the new optocoupler back in listened again, then put my contraption back in to make sure.
Yeah, O.K. I get it, well if anyone is thinking of getting a new optocoupler, give my nutso idea a try, you may be surprised. Sorry I had no advice for the PR ( I love those amps by the way, I think they sound amazing anyways).