Marconi TF2650 FET meter

[Nick]

What type of diode would be needed - the one mentioned on the circuit looks obscure : 'BAYP795'?

I would have thought that pretty much any small silicon small-signal diode would do. 1N4148, 1N914 etc.

I wouldn't build this on Vero or similar strip-board - with the enormously high input impedance of this hybrid, I'd use "Manhattan Style" as favored by RF builders...

Then encase the board in an FR4 box (easy to make) - solder M3 nuts into the corners to bolt the top on - before screwing the top down, spray the board with a conformal coating to keep all the rubbish out...

Vero might "work", or seem to, but is unlikely to be very accurate and will affected by humidity, track capacitance & stray RF etc... that's why the hybrids were made...