"DanF" wrote in message
oups.com...

Jon Yaeger wrote:
I'm contemplating using a pair of 6AU4GT damper diodes for a full-wave
bridge, with a 700 VAC CT tranny.

Yet the spec sheet for the tube has these limits:

Heater positive with respect to cathode:
DC: 100V
DC + Peak: 300V

Heater negative with respect to cathode:
DC: 900V
DC + Peak: 4500V


I assume that during an AC cycle the cathode will "see" -350 volts
relative
to the heater which would normally be operating near ground.

Looks like I'd be in trouble without floating the filament at a minus
potential.


You are over analyzing this... In a simple full wave B+ supply (2
damper tubes with ct of transformer being ground) the cathodes are
ALWAYS positive with respect to the heater (so that means that the
heater is always negative with respect to the cathode). Heater is at
ground potential, cathode at B+ potential.
You are correct about all of the advantages that tube rectifiers have
over solid state. The only drawback to them is that most consume A LOT
of heater power; but if you have extra heater winding current to spare
(or extra space to mount another heater transformer) then by all means,
use them. They sound nice!
For more info, get a copy of "Vacuum Tube Valley" issue # 12. There is
an article about using damper tubes for rectifiers.
Hope this helps... Daniel


Jon,
Daniel is right. I'm planning on using the same on my next project
(someday!). I've characterized many different types for voltage drop (the
dredded "sag" refered to elsewhere in this thread) and the 6CJ3 is an
absolute beast, damn stiff for a tube. The 6AU4 is no weenie either but I
think the newer 9 or 12 pin compactrons like the CJ are newer lower
impedence designs. Good luck!
Mark