[time-nuts] VHF-UHF Frequency Calibrator

[ed breya]

That's an interesting unit. You may want to take a close look at the 
small axial-leaded component going from the tube socket pin 7, to the B+ 
feed-through cap adjacent the "C18" label on the chassis. It appears you 
have it as a choke in the schematic, but I believe it's a diode - 
specifically, a step-recovery one. Our old friend the SRD shows up in a 
lot of places. You can at least check to see if it's a diode, and intact.

That would also explain how a "regular" pinned tube and socket combo can 
provide any meaningful power output to 11 GHz. If it was an acorn or 
lighthouse tube or something like that, I could picture it, but I'd say 
the tube is just pumping the 50 or 100 MHz into the SRD, which is doing 
the multiplying. The RF current path would be through the SRD, the 
feed-through cap into the chassis, then to the output tank, then back to 
the socket pin via the stout cap, which looks like a solder-in type 
feed-through rigged for coupling - almost as good as a leadless cap.

Whatever you do, be careful while poking around in there. With the diode 
hanging off B+, a simple shorting mistake could take it out.

Good luck.

Ed