Need audio for my Vario's

I have a Cambridge and early Ball varios but neither one has the
external audio units.

Are there schematics for these circuits so I can build a couple.

I do have a fried Cambridge AU20 audio unit that has a blown capacitor
on it but it seems that these circuits are very simple and should be
fairly easy to make some for my vario's since I do not think they are
sold anymore.

I also have a vario audio unit that has the static & pitot lines going
into it as a separate unit for audio only, and I do not think it is
working either.

Does anyone have any suggestions? or do I have to buy 3 Borgfelt B50
varios to get audio again.

Ray Buhr