RE: Rectifier/NST Protection

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Pete Komen by way of Terry Fritz <twftesla-at-uswest-dot-net>" <pkomen-at-zianet-dot-com>

Josh,

According to my old ARRL manual, diodes in series need both a swamping
resister and a bypass capacitor across each diode.  The resister balances
voltages across the diode stack.  The capacitor protects against differing
turn off times and passes HF spikes around the diodes.  If HF bypasses the
diode, it must end up at the NST.

I was pondering something similar using 1N4007s with a 3 megohm resister and
a .01 microfarad ceramic capacitor in parallel with each diode.  3 megohms
gives a current about 10x the leakage current. of the diode.

Pete Komen


Hi all!,

I have some questions concerning a full wave rectifier connected to the
output of a NST and how it compares with an RC Filter like Terry's.

1) Would the rectifier eliminate any need for the filter array? I believe it
would, since diodes only allow current to pass through in one direction. I'm
already planning on building a filter regardless, but I thought it would be
fun to throw in a couple hundred diodes with my order to Digi Key in a
couple
of days.

2) What are suitable diodes for this application? I have already narrowed it
down to the 1N4007--- line, but there are 4 pretty cheap ones that look like
they might just work. They are: GCT, DICT, MSCT, and GICT, if there is any
important distinction between them (besides cost)? I'd rather go with the
cheapest ones (which are 1N4007GICT -at- $0.032 a piece, they're normal
silicon,
compared with silicon rectifier for DICT & MSCT (if there's any difference)
and glass passivated (whatever that is :-))for GCT. I'd like to steer clear
of the glass stuff (it's more expensive -- $0.104 a piece 8^0)and since
there's only a $0.002 difference between the last three, I can afford to
drift :-)

3) How 'immune' would a 20 kV rectifier be against the RF of the primary
circuit? RF is always destroying NSTs and I though that maybe something
similar might happen with a rectifier of this type.

I would basically wire at least 20 in series (6 kV tranny) for each leg of
the transformer, giving a safety factor of about 2.3 (should I go higher?).
Using the advice from Sundog and others, I would include a 10 megohm, 1/2
watt resistor between each diode, for added safety. It has also come to my
attention that the tank capacitor will still be fully charged after the
power
has been removed with a DC power source, but won't the resistors in the MMC
just bleed off any charge? Thanks ahead of time! I'll be sure to have some
more questions later as I continue building my TC. Whoa, 1 AM... better get
some more coffee... :-)

Happy Holidays!

- Josh Hunsaker -

Denver, Colorado
Email/AIM: MaverickIce00-at-aol-dot-com

BTW: I found a couple of guys who 'think' they might have a suitable tranny
for me, and with any luck, I should have a tranny by the end of this week,
although it will be tough, with the holidays just around the corner...