[Tubeglow20]

I believe this set uses a 50L6 output tube. I would test the tube or try another tube. I recently did one of these sets and replaced the capacitors and resistors and rebuilt both IF transformers. Radio would play great for about 2 minutes and start to distort. I tested the 50L6 output tube and it tested good, but it the sound would distort after the tube warmed up. Replaced tube with a different one and radio plays great for hours. So I would try another tube and see if that helps.