(SOLVED)1968 Fender Twin Reverb Optoisolator / Vibrato Issue

[Planobilly]

Hi guys,

Any way to test the optoisolator in a Silver Face Twin?

I just rebuilt the amp and everything is working well except the tremolo.

BTW, the Tube Amp Doctor TAD 7025 WA and the F&T caps were great with zero noise. Never had a NOS RCA 7025 but they can't be much better.

Cheers,

Update: New optoisolator...replaced plate cap on v5...now back to normal

Billy

[gadget73]

Whats the optoisolator in use?  I've got very little experience with them, but I think some guitar amps ran the same type as my Sound Tech 1700A uses.  In the ST, its more of a light controlled variable resistor.  If you can turn up the spec sheet, it should have a chart that cross-references input voltage to output resistance. 

http://www.muzique.com/news/clm6000-replacement/

Not sure if thats what yours runs, but it seems to have been a common one for that job.  Its what the ST uses as well.  Basically by that sheet, you should see about 500K ohms across it with no input to the LED, and 500 with the LED being fed 2 volts at something under 40ma.