"Avery Fineman" wrote in message
...
In article , "Tim Wescott"
writes:

Your solid state devices will either be really light-weight or will have
significantly higher capacitances than the tubes, so it would be very
difficult to get your oscillator to track.

-- snip --
On checking the HV supply of this little receiver, the OB2 strike
voltage had increased beyond manufacturer's spec so it did not always
strike and start regulating with power-on. The lone OB2 in spares,
also 40 years old, was just the opposite, striking below spec.

Antique Electronics Supply has good replacement tubes -- but solid-state
regulators for old tube equipment is more fun, kinda like putting EFI on
your flathead Ford engine (no kidding, it's done).

-- snip more --
With a 6.3 V filament arrangement, that would be on the hairy edge
of regulating at -10% AC line voltage. Filter capacitor needs to be
high enough for only 5% ripple and rectifier diodes can't be much more
than 0.7 V forward drop to fit the minimum 7806 regulator 2 V head-
room.

I would use a new LDO regulator, if I used one at all. On thinking about it
after my post, it occurred to me that for the filaments I would be happy
with a well-filtered DC supply to keep the filament hum from modulating my
RF. If all you have is a 6.3V supply you need really low-drop diodes,
however, and your filament transformer's RMS current will go up no matter
what.

Note: The original AC filament voltage was made within certain
(seldom specified) limits; if that is on the low side also, the 7806
may poop out during droops in ripple voltage. 7906s were originally
made in the series for negative voltage regulation, also good for
providing a minus bias voltage. Tube filaments for indirectly-heated
cathodes don't care about DC polarity. Slightly-lower than nominal
voltage will improve heater life.

But can decrease cathode life if the cathode current is high -- even oxide
cathodes don't like being temperature starved. Check some of the warnings
and recommended start up procedures for 10kW transmitter tubes for some
_really_ tight cathode care-and-feeding instructions.

-- snip even more --