Jim I have similar problems with vintage receivers. I had taken down my Kenwood receiver and stored it away while I cleaned up my Sunporch room. Months later I found an RCA Jack plugged into the Dolby in Dolby out ports I figured when I disassemble thcomponents attached to it I didn't want to lose the jack so randomly plugged it onto the first jack I could while moving stuff around. Bout 5 months go by, I clean the potentiometers on the Kenwood because they were cause static and volume issues. This is one of the Monster Recievers Kenwood made and even with my power Hungry Dahlquist speakers, It still can be deafining at medium output. So I was quite surprised after cleaning, even at full power the sound on any speaker attached, was very low volume. I went onto AudioKhama web site, got help from the best, reread the original owners manual and the service manual. Got so frustrated as it work perfectly before being store 5 months. I left it put it away and did something else. Wioke up one night and thought about the RCA jack. Next day reread the manual. It says you need jumper cable on the Dolby in and out puts. Every othere receiver from Marantz to Pioneer, ect from this 70's era of analog receivers have main input and out put s that if aren't going to a separate amp, need jumper cables connected from input to output side. Once I figured out this(mind you this beast has a ton on rca jacks for multiple turntables, 3 sets of speakers, aux, 2tape recorders, list goes on) so seeing dolby in and outs did't trigger my brain as something to pay attention too, any works fantastic! Sometimes walking away is much better than a hammer or gas and a match...Great Job.
PS you are the guy to buid the indy Watson!