I had an FM3 for awhile. I went through it and replaced all the cooked carbon comp resistors, all the caps Van Alstine recommended, matching everything critical, mil-spec versions of the tubes... Tuner punches way above its weight esp if you don't cut corners the way Dyna did to meet their desired price point. I sometimes regret selling mine, but there are maybe two radio stations broadcasting music I like (mostly jazz and some classical) in my area with high audio quality (and one is talk programming most of the time) so it wasn't getting much use. I have a pretty good collection of documentation including a pdf scan of the user manual, Frank Van Alstine's excellent write-up on FM3 restoration, and a Dynaco bulletin on a substitution for the super-rare EMM801 tuning eye tube. If you'd like any of those, PM me with your email address and I'll be happy to send them.
BTW I think the mod you asked about was intended to improve selectivity, not sensitivity.
One potential Achilles heel FVA has mentioned on the forums here but is not in his article: In order for the Dyna no-instruments-required alignment procedure to work, the first IF xformer must be tuned to precisely 10.7 mHz- unlikely if the tuna has a lot of hours on it. A TV or radio repair place (if you can even find one) or ham radio operator may have the necessary instruments. Good luck with your projects and welcome to AC.
