As old coot said LIGHT tapping of tubes is a good start. Also you can
lightly push the tubes to look for dirty / bad sockets. Its all about
localizing the problem .......
On sets built with PCB's & a steel frame the boards are soldered or
screwed to the chassis. The steel is a huge ground & all those mounting
point need to be good. Also look at shields around the IF's. They often
complete grounds & get cold joints.
One last tip. Tube pins can be cleaned with dikes. Lightly grab the pins
& shave them. For the sockets as a last resort you can tighten most of
them with a jewelers screwdriver form the top.
What the hell, one more......
RCA tuners. To clean an RCA tuner especially one using the Nuvista
RF amp tube. Pull the tuner & remove both shields. ONLY put a small
amount of cleaner on the contacts. DO NOT just spray it ! Most cleaners
would turn the RF stage into an oscillator ! It was the first mistake I
made at the bench. Hell I didnt know ! The boss was cool about it. Had
to douche out the tuner with freon then trim the neutralizing cap.
73 Zeno
LFOD !