[RodB]

You can start with the 2 tubes that are used in handling FM, 12AT7 FM converter and 19T8 Detector. If they are OK then S2 the AM/FM switch switches B+ to the 12AT7 converter. You should see plate voltages on that tube when in FM. Measure the voltages and compare to voltage chart. You should see a negative voltage at the FM discriminator circuit when feeding a 4.3 MHz carrier in the FM section. The voltage should vary with signal strength. That should keep you busy for a short while. GL.