Hi, Randy!
I hope this will help you with your problem potentiometers. It sounds like these are exhibiting the symptoms of "dirty pots." If this were *my* SCA-35, I would remove the potentiometers from the amplifier and do a thorough cleaning regimen on them. IF YOU ARE CAREFUL, you can clean them "in-place," but be prepared to clean up a mess.
You will hear all sorts of stories about the BEST cleaners and lubricants to use. I can only give you the method that *appears* to work well. If your potentiometers are still noisy and intermittent after trying this method, you will *probably* need to replace them. (Not necessarily an easy thing to do nowadays.)
OK, before you clean 'em, you need *something* suitable. I suggest you purchase a can of common lighter fluid (which is naphtha) and then go to your local Radio Shack and purchase their deoxIT kit. The kit will contain deoxIT DN5 and deoxIT GN5. First, SOAK the control with the Lighter Fluid. Work the control back and forth through its rotation. Douse it again with Lighter Fluid and work it back and forth again. Shake the excess Lighter Fluid from the openings in the control. Allow it to dry.
Next, get the little spray can of deoxIT DN5 and spray it inside the control. You don't need to douse the control, just a good spritz. Work the control back and forth a little and allow the control to "sit" for a few minutes (approximately 2 to 5 minutes works well). Then another small "spritz" of the DN5 along with more "working" of the control - back and forth. Allow to dry.
Now, douse the control with Lighter Fluid again. REALLY soak it and work the control back and forth again. Shake excess Lighter fluid from the openings and allow to dry thoroughly.
Finally, spray an EXTREMELY fine mist of deoxIT GN5 "contact conditioner" into the control and rotate it back and forth a few more times. The key here is to apply a REALLY fine mist. Less is more here. Ideally it would be good to get a coating that is only a few molecules thick, but you'll just have to "wing it" to get close. If you slip and douse it, clean it with Lighter Fluid again, allow to dry and follow it up with that teensy mist of GN5. Repeat with the rest of the controls. That's it!
Do NOT buy anything else. Don't try to "go cheap" with Radio Shack's own products. (Nothing against them, but I've never had much luck with them on potentiometers.)
Chances are, this will improve things, or perhaps *eliminate* the problems completely. Make SURE you let us know how this works out for you!
Sincerely,
Bill Thomas