Jon Yaeger wrote:
in article , Bret Ludwig
at wrote on 10/1/05 11:09 PM:
Thanks, Bret, that's all good general advice, but perhaps in my ignorance it
seems that your answer is somewhat peripheral to the question.
My interest in using these tubes is that they are reputed to produce the
smoothest rectification. Because the cathodes are indirectly heated, there
is an 11+ second warm-up time, which makes life easier on the cathodes
downstream. Solid state rectifiers have their advantages, but I want an
all-tube circuit here, EMP notwithstanding. With plenty of current
available but no active regulation.
You state that specific shielding is needed. Would that be different, say,
from a 5AR4, and if so, kindly elaborate . . . . .
Well, if EMP is anticipated, you are looking at voltages generated
along a gradient so that if there is a loop formed by the layout a
large differential can be developed across, that's where it will. What
you are doing is the same basic thing done to reduce M-field
interference-only much more carefully.
I don't think smoothness of rectification is any better with a damper
diode than any other tube, and I don't think smoothness of
rectification is that critical IF you filter your supply properly. I
wouldn't even spend any extra money on HEXFREDs. I would put my power
supply on a subchassis or a whole different chassis if I were really
serious, and I would heavily bypass all my lytics and put a RF choke in
the supply path.
Your heater supply should be fully energized at least one whole minute
before ANY B+ whatsoever is applied for best life. You could use time
delay relays or separate manual switches, whichever floats your boat.
A tube rectifier of course will work fine, but if you want the maximum
theoretical life you will have to provide for its slow warm-up as well.
It can get complicated.
Of course there is the alternate view, which is to say "screw it" and
build for simplicity. You will go through more tubes but if everyone
does that way they will keep making them and the price will be lower.
With the CRT industry on the verge of stand-down in general this could
be an important point-or the reduction in materials supply may end
receiving tube production altogether. hard telling.