Paia Theremax

[jezz]

I've got a bare PCB for the Theremax that I'm mhoping to finally build, so
I've been checking the availability of some of the components in the UK.

1. Does anyone know how critical the use of 1N34A germanium diodes in the
circuit is? The diodes are in the ring (de)modulator for each of the high
frequency oscillators, used to determine the frequency difference between
the pairs of oscillators. Could I substitute silicon diodes of some sort
e.g. 1N4148?

2. The coils are listed as 796kHz - I can get 100uH, 470uH or 680uH from RS
Semiconductors for that frequency. Any idea which?

3. C14 and C18 are listed as "68pF ceramic, NPO". What's NPO? Can't find
anything like it in the catalogue and the notes at paia's website make
reference to problems if you don't use NPO caps. They're part of the HF
oscillator circuit along with the coils.

Many thanks for any help you can give.

jezz.