How about a radio like the bottom one, that is fine volume wise then all of a sudden the volume drops then rises again?? Easy fix or is it off MN?
Hmmm, I have not seen that problem before. Check all of the grounds and the antenna and make sure all connections are good, clean and tight.
If that doesn't do it, I'd have to look at it.
It could be a bad tube. If you're comfortable replacing tubes yourself, they're all available (except the 0Z4) on ebay pretty cheap.
I can make a solid state replacement for the 0Z4. Retubing it may take care of that issue.
If not, let me know and I'd be happy to look at it.