Forgot to add- the output coupling capacitor is 100pF, a low value was deliberately used to minimise the amount of transient energy that could be coupled into one of these rather nice little counters. Most seem to have a couple of back-to-back SMD Si diodes across the input, but discretion is the better part of valour. The minimum 1st LO frequency of the 750 is 2MHz, 100pF seemed about right impedance-wise. I'll get round to adding that low-impedance succceeding buffer one day! The 0.5pF cylindrical capacitor with long silver-plated leads was from Birkett's stall at a rally long ago, he had bags of about 30 for a quid and I couldn't resist- finding bags of 0.5pF caps seemed like finding bags of phlogiston lol. I'm sure a cm or so of twisted wire would have done fine but this was a physicaly rigid component for this inter-reaching "free-space" situation.
https://www.radiomuseum.org/tubes/tube_5678.html