Hi Fred,

Another option: instead of paralleled conventional
diodes, use zener diodes in series (opposing).
Then, five 3.6-volt zener-diode pairs would
give close to your 18 volt output range.

This seems to be the most practical idea; I'll try
that soon and report back.

Thank you again!

Tom

P.S.: Probably the spec sheet of the final amp
will look somewhat irritating: "It utilizes 7
electron tubes and 25 solid state diodes..."

--
fnord (now you see it, now you don't)
- R.A. Wilson / FZ