Follow-up on my previous post: The gremlin noises got worse and volume on the eBay pot got wackier. After all this recap and new volume control work, I was really frustrated. Contacted Mark at Old Radio Parts (mentioned on this site) and he built me a dual 25% tap pot without the switch (for less $ than the eBay pot, I might add). Because of the scarcity of old parts, he could only make 1meg, but said it should be fine to replace the original 700K. The pot had long leads and soldered right in place, so it did not require making pig-tails like the eBay pot did.
After I swapped it out, I still had issues - really weird stuff that changed up when adjusting the COMP and MODE switches. I called him and he was extremely helpful. He said he's seen this many times, when customers suspect the new pot but sometimes it's a compound problem that had to be elsewhere. After listening to his advice, he was absolutely right!
Dove back into the unit and noticed the MODE SELECTOR was a mess - solder joints were awful and as I probed further, half the switch crumbled (old thin plastic) No way to replace that one but the only useful feature of that switch to me is Stereo to Mono - the rest is just superfluous. Many connections of critical audio getting flipped every which way by a weak 50-year old switch - not good. I bypassed the switch altogether and the gremlins noises disappeared! Then I was actually able to tie L&R back to the old switch where Stereo is switched to Mono, as luckily that portion still worked, noise free. The rest I can live without if it means no gremlins.
After all that, It still was not perfect. When I changed the 3-position COMP switch balance would shift and sometimes a channel would go out altogether when the volume was adjusted. D-oxed that switch again, but took my time and really got in there. And lo and behold, the gremlins are gone and that volume control and COMP selector now work perfectly. Finally!
I cannot say enough about the pot Mark built and his great support. Superb - USA parts - smooth, gradual, solid volume control. He can build one with the AC switch, but for me, avoiding having AC switched that close to the audio circuit and not having to worry about AC shielding makes sense. Also, it's great having the full sweep of volume without the switch.
So the lesson here is that volume control issues on these old MA6100's can be compound in many areas - controls, switches, grounding, solder joints - etc - something to consider before diving into a recap. I have never been happier with my MA6100 - it gives me daily listening pleasure and I can finally say it's trouble free.... for now!! LOL.
