No, plugging something into it will send the signal through a different path than the dirty/tarnished contacts, so that alone won't reveal anything amiss. Just run the brush in and out a few times, and then wait to see if it cuts out again or not. Sometimes, beating heavily on the top of the cabinet (around the center area) with your fist will cause a dirty/tarnished FX loop jack to crackle and pop. The vibration will ever so slightly jarr the contacts and make them crackle as they gain and lose contact intermittently (but sometimes not!).

Without actually pulling the chassis and inspecting stuff, it's a shot in the dark kind of diagnosis. Let us know if it cuts out any more after brushing it out, and we'll go from there.

Thermionic