Scott, re? ?V8, I see it is called an FM limiter and AM detector, which is confusing; and now I see that the Plate and Screen voltage is switched by S1-BB? way over …so I believe V8 is switched to function between a FM limiter or an AM detector. The screen and plate voltage are both reduced [some books say 30 volts typical] for operation as a limiter. Perhaps you can measure that that band 5,6 FM ?reduces

? If not, it might have too much gain .? just a thought

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I started looking at the manual and saw that it has a Multiplex out phono jack.

You might want to look/listen to the FM audio from there, which is before the switches, then you should know if the problem is in the limiter /discriminator or Not.

Likely so, but better to narrow down with confidence.

Seems to me, a sweep gen and scope might be needed,? but the usual? look and probe might reveal something

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