[Radioroslyn]

Hi and Welcome,
Just for grins unplug the spkr plug from the chassis and use your ohm meter to check the resistance from one pin (doesn't matter which) to the other three. If all is well you should see a fairly low resistance like less than 4,000 ohms
If you find something like 10,000 or a meg ohm this would indicate a problem.

Some common issues w/the 20 are: open(bad) field coil, output transformer primary, primary of the rf coils (easy to fix) and audio driver transformer.

GL