[RodB]

Generally, FM uses the same circuits as AM from the detector back to the speaker. Get the AM working, then monitor the FM discriminator cap voltage, which is the small electrolytic at the FM discriminator diode. It's the AGC, equivalent to the AVC in AM. Send a carrier signal at the IF frequency to the FM front end and you should see the AGC voltage vary with signal strength. FM will use a separate set of IF transformers, often mounted in the same can as the AM, but the same tubes as AM. The band switch will select which transformer to use. Often the switch will cause problems.