This is my first post as I am a new member. I recently picked up a 5590 at a yard sale for 20
dollars. Yes, lucky me. I bought it off an ex-airman,
who took great care of it. I had seen it on a shelf in the garage and commented on the size ,and, he said
"That old thing, 20 bucks,the left side sometimes cut in and out until you mess with volume control" I waited 10 minutes for him to find the owners manual, no luck, but he did find a nice schematic for it. Anyhow I found that if I pushed the 30hz filter in the sound would cut off as I could hear click then as I turned the vol back down click and sound again .
Does this sound like dirty switches? Also the speakers I had tested it on are small,Could it be a protection feature since the speaks are too small?
Please forgive my novice explaination and thanks
for any input.

rather than try to 2nd guess what's wrong you should just open it up, clean it out and service ALL switches and controls with your fave. contact cleaner(most here like deoxit).

Thanks, I was unsure what would be safe as far as chemicals go. I ,will take your advise.