I try to live in accordance with the ancient proverb, "A journey of a single mile begins with a thousand blunders."
With just a few more blunders I'll be finished with the Coronado 575 journey.
I installed the 1-Meg audio pot (switched) as advised. That went in the front volume control position. After much experimentation, I replaced the original RF pot with a 1-Kohm linear pot. I couldn't bring myself to drill holes in the cabinet, so it went to the back of the chassis. I also have a 20-ohm 25W line voltage dropper, and I added a toggle switch for that. I think this represents what I did:
One other change was that I had a 100K resistor for R9, and I changed that to the correct 250K. The final wiring (except for the toggle switch) looks like this:
The controls at the back of the chassis:
A quick before/after picture:
Everything works well. Very good reception of local stations with a 12-inch wire antenna, exceptionally sharp tuning at the precise frequencies on the dial, and no noise between stations.
Unfortunately, the audio quality is not so good. I can only describe it as "buzzy." The distortion is what you would expect from a damaged speaker cone, but the speaker seems to be in perfect condition. Here's a link to a 15-second audio sample:
https://flic.kr/p/22umN23
It sounds a bit worse in real life. Please let me know if you recognize what the problem might be.
If anyone is interested, this is a link to a Flickr album with 15 additional photos of the restoration.
https://flic.kr/s/aHsmbhh8ct