[Marsupial]

I am not sure about 7N7 to replace 7AF7 - is it listed somewhere about being a valid substitution?

I know they are both dual medium mu triods... and I am really not an expert substitution guy, but what the schematics tell me is that the 7N7 heater uses twice the current that the 7AF7 does; that could cause issues I guess.

I know the Sylvania 7af7 specsheets state that the specs are similar to the 7N7, but also point out the lower interelectrode capacities.

Your bad value caps as well could cause issues, depending what/where they are. I'd start by that and see where it goes.

But really, the best is to follow the steps in the service manual. It was made to diagnose what's wrong on the radio and pinpoint what to change.