[Eliot Ness]

Lots of good ideas here Joe. No harm in testing your tubes, but if you have spares the best test is to swap them out. Also make sure each tube socket connector is clean and tight (small paint gun cleaning brushes work well to clean). Also clean your tube pins, it has probably been years since the contacts or tube pins have been checked/cleaned (if ever), and don't forget the grid caps and connectors on the 24's.

Next I'd reheat and reflow (with a little fresh solder) all the solder joints; they might look OK on the surface, but under that glob of 80 year old solder a cold joint might be lurking...... and remember to check the tuning cap screws as mentioned in that video. A bad ground that looks OK to the eye has been the cause of a lot of strange problems.

That's the easy stuff you want to do first; if that doesn't work it's time to roll up your sleeves and start some serious troubleshooting. Good luck, you can do it!

Here are links to some inexpensive brushes that are great for cleaning in tight spots (just add some of your favorite contact cleaner):

http://www.harborfreight.com/5-piece-air...68155.html
http://www.harborfreight.com/10-piece-tu...95947.html