Date: Fri, 22 Dec 2017 08:37:01 -0500
From: Ron Youvan <ka4inm@gmail.com>
To: amps <amps@contesting.com>
Subject: Re: [Amps] Henry 2k-4 HV inductor
< The primary advantage of using a L or Pi filter (rather than a brute
<force {just capacitance} filter) is the reduced amount of energy stored
<in capacitance which is undesirable when an arc is experienced.
<The extra storage energy and the lack of inductance (which reduces the
<amount of extra current from the rectifier/s) add to the amount of
<energy that shall be dissipated in the tube/s or other fault.
< It is a safety thing. (for the tube/s)
<Pi filters are seldom used for low Voltage supplies (100. Volts and
<under) because little "arcs" at these Voltages.
--
< Ron KA4INM -
## IF the GG triode arcs from the anode to the grid.... which is
bonded to the chassis.... then the tube is probably defective
anyway. If you hi pot test the tube, just prior to the arc event,
you will find that it hi pot tests on the low side...like way on the low
side.
## You dont require the huge dc resistance of the choke to limit the
peak fault current either... which wont work anyway, unless the choke is
dead last. The dead simple method is to use a 50 ohm
glitch resistor in series with the B+. And precede the 50 ohm glitch
resistor
with a fast HV fuse. Max fault current is just B+ dcv divided by 50 ohms.
## EG, 3000 vdc / 50 ohms = 60 A fault current. For a table top amp,
use a 750 ma to 1 A rated HV fuse. The 60A of fault current will open off
a 1A
rated fuse in less than 2 msecs every time.... event over. And no follow on
current
from the rectifiers either.
## The 60A fault current will be there, regardless of the HV capacitor value.
The HV fuse will open off in less than 2 msecs, whether you use 25 uf..or
312 uf.
I have tested the concept 8 ways to sunday. Tested 8 x 200 uf caps in
series..and
also 8 x 2500 uf caps in series. Filter cap value has no bearing at all.
## Also tested using 20 x 2000 uf caps in series on a 6700 vdc supply, same
results.
Also tested on a 8 kv supply using 24 x 3900 uf caps in series.... also
using a 50 ohm
glitch. Both the 6700 + 8kv supplies use a Buss 3A rated HV fuse. Same
deal, 3A
fuse open off in less than 2 msecs every time. 6700 / 50 = 134 A fault
current.
8 kv / 50 ohms = 160A fault current. 134A / 160A fault current opens off
the 3A rated
HV fuse stupid fast. On the 8 kv supply, the concept was tested at least 11
times.
Nothing happens...except for an open HV fuse.
### Its 2017, and chokes, resonant chokes have gone the way of the do-do
bird. Put the
money + weight into the HD quality xfmr, with either a doubler or a FWB..and a
high C
filter cap, HV fuse, and 50 ohm glitch Resistor. If you want bomb proof,
then install a 2nd
HV fuse.... and wire 2nd hv fuse between plate xfmr secondary + diode board.
2nd HV fuse
goes in just ONE leg of the sec. Ok, now you can short the B+ to the B-....
or B+ to chassis,
right at the HV filter, and nothing happens, except for open HV fuse #2.
Diode board remains intact.
We tested that concept several times as well. The HV fuses are fast and
cheap, and faster
than a HV mech relay or even a sped up vac relay.
## I use a HV meter in the HV supply, wired directly between B+ and B- of the
filter cap. 2nd
HV meter is in the RF deck, between B+ and B-. HV meter in RF deck is AFTER
the 50 ohm glitch.
HV meter in B+ supply is BEFORE the 50 ohm glitch and mating fuse.
## IF the HV fuse associated with the 50 ohm glitch opens up, the HV meter in
the RF deck will read
ZERO ! However, the HV meter inside the B+ supply will still read normal B+
voltage level !
IF BOTH hv meters read ZERO, then you know that the 2nd HV fuse, between xfmr
sec and diode board,
has gone open. I also use a magnetic hydraulic circuit breaker in the
incoming 240 vac line to B+ supply.
These are the super fast trip type, with the oil evacuated from the internal
oil reservoir. They are known as
instant trip or NO delay types. They do not rely on heat activation like a
normal breaker. Ok, no you can
lay a dead short across the sec of the plate xfmr..and breaker open off asap,
xfmr remains intact.. also tested
that concept out several times.
## With all of the above installed, short anything, anywhere you want, and
everything remains intact.
Breakers are cheap, HV fuses are cheap, ditto with the 50 ohm glitch resistor.
Jim VE7RF
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