Vactrol longevity query.

[digi2t]

Hi all. I've got another Foxx Guitar Synth (glorified Mutron III) on the work bench right now, and apart from some bum components, it seems that the Vactrol is on the slide as well. If it sits for a few hours, and I turn it on, it plays nice for a few minutes, but then the frequency response starts to slide. Eventually, it goes past where the trimmer can correct, and takes me into oscillation territory. Putting my finger across two of the leads of either LDR brings it back, since my finger is acting as a resistor.

So my question is this; do Vactrols "age"? Do they drift with time, or get to a point where the photocell can just go out, even after a few minutes? Can they degrade to the point where the light from the LED can destabilize them?

It's gonna suck to have to change out the Vactrol, since it still has the original one in there. 

[PRR]

LA-2s made in the 1960s are still running the original optos.

Your pedal can't have more hours on it than a broadcast limiter racks up.

I would re-study all other parts first.

[digi2t]

LA-2s made in the 1960s are still running the original optos.

Your pedal can't have more hours on it than a broadcast limiter racks up.

I would re-study all other parts first.

OK, thanks Paul. Just something that crossed my mind, so I thought I would throw it out there. As your point states, they should last. The Mutron Flanger I had was of the same vintage, and the opto worked fine. I'll double check the resistor values around it first. I already found a 1M resistor that was way out of spec (read over 4M on my DMM), and one of the quad opamps was dead. Replacing them brought back most of the life to it. The opto straying is the only thing left now.

[R.G.]

It's more likely to be a longevity problem with the light source than the LDR.