vintage 1176 rev A - intermittent GR bursts?

[outoftune]

am checking out a problematic vintage blue stripe 1176...passes audio...the compression has become intermittent...it's happening in bursts and it seems like i need to crank the input knob way up to get anything. im just feeding it a sine wave and its jumping between no GR and 20db randomly.

im suspecting a 2n3707 transistor in the side chain amp that feeds the fet. the attack and release and ratio controls are working...i've checked for intermittent connections and haven't found anything.

anyone seen this issue before?

 

[radardoug]

Does that one have the GR on/off switch on the attack or decay pot?
Might be as simple as old age in that switch.
You could scope it on the rectifier side of the switch and see if the audio cuts out.

 

[outoftune]

doug...thanks for the suggestion...checked that but it is a newer switch...the unit seems to have been recapped / serviced at some point (new caps, couple new pots)

after more poking around it seems to be an issue with the FET itself...the audio path is fine and the sidechain amplifier seems to be putting out a healthy signal...i've ordered a matched FET pair so we will see if that does the trick.