Speaking of Merlins

[Eric]

>         If memory serves correct, zeners drift with temperature. 

A shame that you aren't working in the vacuum domain.
The glass analog of the zener diode, the gas-filled
voltage reference, is vastly more stable and reliable
than zeners. It's especially suited for high-current
operation, and requires NO heatsink. A typical OD3
gas diode will handle 40 mA for tens of thousands
of hours. 

Unfortunately, gas diodes only come in voltages of
75, 90, 105 or 150 volts. The common types, anyway.

(5651s and corona regulators can't handle much current.
Victoreen once made a corona diode that broke down
at 950 volts DC. Used in geiger counters......)

Let's see.....150v times 40 mA = 6 watts.
Come to think of it, 50w zeners are getting really
hard to find for some reason.

Well Batz, have you tried those tubes I sent you?