I've read quite a lot about this tuner and the list of things contributing to hum is a long one. I know that hum is often an issue of bad grounding so I attacked that first. Using the schematic I reflowed all the ground connections on the bottom of the boards and those to the volume pot on the top. I then noticed on the assembly diagram what appeaed to be a solder bridge from eyelet 37 on the PC-8 board and the chassis. I decided to try to fashion a chassis grounding strap using desoldering braid from eyelet 37 to the nearest bolt on the chassis. I also was able to resolder the loose tube shield grounding strap to the PC-8 board for V6.
Everything looked pretty good, so I put the bottom cover back on and gave it a test drive. All the hum was virtually gone! So, I don't know what if anything I did directly helped the problem, but I am very happy with the result. I really do like this little tuner for our local jazz stations.