[GreenKeys] (no subject)

[WA5CAB at cs.com]

Joe,

I can't speak to what might have continued in civilian practice but for a 
tube based loop supply I think you are going to have to go back to the early 
30's.  During WW-II and Korea, almost all of the military loop supplies I 
think I have ever seen used dry plate rectifiers, copper oxide in the late 
30's and selenium after that.  I think I have seen (physically) one loop supply 
that used either Tungar or mercury vapor rectifiers.  But it probably dated 
from around 1938.  The other military sets I've had all used selenium 
stacks.  I don't think anyone makes selenium rectifiers anymore.  They have a 30 
to 50 year shelf life.

If you are only going to run one or two 60 mA loops, you could build a loop 
supply using a 5U4 or 5Z3 but you would be about as EMP proof if you used a 
garden variety 1 KV  1 A silicon full wave block and be able to supply a 
standard 5 or 6 channel switchboard.  Tubes aren't totally EMP proof.  They 
are just one or two orders of magnitude better than CMOS.  Put 1 KV across a 
1R5 or 3S4 and watch the fireworks.

In a message dated 5/5/2009 10:53:29 PM Central Daylight Time, 
amourdutigre at kc.rr.com writes: 
> Now, I need to be aimed in the direction of a tube based loop powersupply 
> circuit without any solid state rectifiers. I have googled extensively and 
> have found nothing. (Presently, I am using a loop supply on loan from 
> K0TTY, and I have just bought a loop supply from Steve Hilsz. (I do not dislike 
> solid state, but I do want to have a completely EMP proof system, and I 
> simply like tubes.)

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480