Testing Vactrols

[highroller]

I suspect a problem with some Vactrols (LDR) in my Mark IV and I'm wondering if there is a way to test an LDR without removing it from the circuit ? Any tips ?

 

[insearchoftone]

I can't answer the question but what are the symptoms that make you come to that conclusion?

Sorry for the newbie LDR question. I would like to learn more about this issue.

 

[highroller]

I got a major power amp level problem with my Mark IV, very low output on all channels, plus no effect on the LD and R1 presence "pull" functions. I tried so many things without success, e.g.: changed tubes, cord in the fx loop, cleaned contacts, tested different speakers, but still same low output. Preamp distortion and power tube voltages seem ok so maybe a Vactrol is dead somewhere in the fx loop or elsewhere that prevent gain to reach the power amp. Or it may also lie somewhere in the EQ circuit, maybe a bad transitor ? Hope to resolve the issues without costly servicing.

 

[highroller]

...sorry, LD and "R2" presence "pull shift", not R1.