i picked up a nice Scepter on friday, and of course the tremolo didn't work even though the seller said it did, that's what i get for not playing it before i bought it. anyway, once i determined that the LFO was working removed the old photocoupler, and i just ended up using a standard diffused red led and a LDR with the largest range i could find. both of which i got at Radio Shack. i found that the real trick is in getting the position/distance of the LED and LDR just right. the LED puts out more than enough light so i put some shrink tube around the LED to limit how much light gets to the LDR and just fiddled with the positioning until i thought it sounded good. i didn't even bother housing it as the the interior of the amp chassis seems to be dark and light tight enough to not need it. while i was positioning the LED and LDR i found it was pretty easy to get a pretty cool hard tremolo that reminded me of the tremolo on my Ampeg Gemini II when it's on the repeat setting.
as always you need to be very careful anytime you work on an amp. i let myself get tunnel vision and shocked the piss out of myself twice in the course of working on the amp. with that said there isn't more than 25volts on the trem/reverb board so if you make sure to always unplug the amp anytime your hands are in it and not rest your forearms on the power switch it's a pretty easy fix.
