It’s fixed! It turned out to be grid-circuit related. Apparently, when I replaced the two resistors at the anode of the thyratrons in the Field Control circuit, I mismatched some of the connectors at a terminal bar. When I originally performed this operation, I went ahead and replaced some of the wires because many of them looked really terrible. Some of these wires were connected to the Grid transformers. Specifically, I had switched one of the primaries of the field grid transformer so it was connected to A25 instead of A24. Concurrently, the secondaries of the armature grid transformer were swapped so they were driving opposite thyratrons.
This came at the end of a marathon repair session where I was giving myself until Friday to figure it out or sell it as-is. I lost my shop in the middle of this and was under a tremendous amount of pressure to get it painted, fixed, sold, and out before the end of April; all while trying to ignore the invisible gun I keep feeling pointed at me that is the COVID-19 pandemic. At around the second hour, I resolved to trace every wire in the serial-matched manual to what my machine had. I started with the compensation circuit because those were among the first wires I replaced when I started the re-wire of the system and thought I had screwed up there. I checked every wire this way and it revealed NOTHING. The secondaries of the grid transformers on the schematic I used are not labeled and the associated voltages were all within 5% when I measured them.
Time to pull my ace in the hole. Russ sent me a PDF of a the factory wiring schematic that shows the wiring topology of the WIAD. It difficult to read, so I went ahead and put the graphic in Inkscape and colored all the traces to make it easier to follow the junctions. At the same time, I labeled the resistors on the wiring diagram and the schematic to give myself one thing to hold in my head. I’ll upload it when I figure out how to shrink the file size into something that PM will accept but is also legible. I started at the top and immediately noticed the problems with the grid transformers. It fixed everything.
I put the entire thing back together and wiped it down. I put the craigslist add up right away and it was gone in less than 24 hours for my asking price.
After I found the problem I came back to PM and found some threads that described similar problems and connected them to the grid transformers. If I had managed to find
this post by Leigh, it would have solved everything. Oh well! For the record, anyone experiencing a drum-like sound when the motor is under power needs to start with the grid-transformers.
What an odyssey! I’m so glad I followed through and was able to fix this, otherwise I would have spent the rest of my life wondering what it was. Thanks for tall the help guys, I really doubt I ever would have been able to solve without all the help. Special thanks to Russ for all the super-responsive PM help. That wiring diagram ended up being the critical tool for me.
