One more post...

This VCO will consist of four PCBs. Two jack boards (much like
what Dieter and Bob WIlliams do), the main board and mounted
to that will be an epoxy sealed module.

I am not trying to pull an Alan R. Pearlman here (sealed
modules) . This boardlette is sealed in heat-conductive epoxy to
maximize temperature stability of the all-important expo
converter, which in turn will greatly improve stability. The tempco
resister is an SMT chip type (SMT tempcos = better heat transfer)
which will be mounted physically directly underneath the 'money'
parts, the matched transistor pair which governs the oscillating
frequency of the core.

Why am I telling you this

This is gong to pull the price up about $5 to 10 USD for the labor
involved in potting these boardlettes - but it will pay dividends in
stability.

- Peter