[TA Forbes]

My 37-670 would play well for a few minutes and then lose volume to the point that you could not hear the station at all. Simultaneously the shadowmeter went completely black. I put off working on it, mainly because it is large, heavy, and a pain in the (thing one sits on) to lug off the relatively high place it occupies, transport to my work table, and take apart. Today I stopped putting it off and gave myself a healthy dose of pain in my (thing I siit on) getting it to my work table and apart.

Long story short: problem was a 6K7G tube (IF amplifier) that tests good on my tester when "cold" but tests bad when "hot."

First time I have had a tube issue like this.

The radio played for over an hour after replacing the 6K7G, so believe problem solved.

Color me pleased and (thing I sit on) sore.

[Arran]

Before you toss that 6K7, try resoldering the pins on the base as well as the grid cap, particularly the cathode pin, I found a 6K6 tube like that lately, tube lit up but no reading.
Regards
Arran

[TA Forbes]

Great advice! I'll do that.