Subject: Re: [Amps] plate voltage meter shunt
-----Original Message-----
From: Carl
Sent: Sunday, November 04, 2012 4:29 AM
To: Jim Thomson ; amps@contesting.com
Subject: Re: [Amps] plate voltage meter shunt
Date: Sat, 3 Nov 2012 14:15:44 -0700 (PDT)
From: Douglas Johnson <w9iix1@yahoo.com>
To: AMPS <amps@contesting.com>
Subject: [Amps] plate voltage meter shunt
I am installing a meter to measure plate voltage 1-5000v@ 1a?dc, the
meter has a 1ma fs rating. ?the serial resistance I have made up in the
past has been 3 watt metal film resistors in series. since they can only
rated for 200v per resistor it takes many to do the job. Can some other
resistor type with a higher rating?be used in a safe manner for this
purpose?...tnx, Doug,w9iix
## it’s a meter multiplier string..and not a shunt ! You can buy 1%
tol 3 kv rated resistors and also 1% tol 10 and 15 kv rated resistor’s...
from mouser. 5000/.001 = 5 megohms. Use 10 x 500K ohm resistors in
series.
I mount em on either perf board or drill out some micarta, plexiglass,
or UHMW. Just mount em so they go down one side,across, and back up the
other side. I mount the entire assy directly to the meter studs !
To pull that off, you need to make the board big enough. The usual deal
is to make it rectangular shaped, taller than wider, then whack two holes
for the meter studs towards the top of the board..with the rest of the
board hanging down.
## you can mount the board in a few diff configs. The idea is to keep
the 5 kv end well away from the meter itself. 5 kv enters resistor
#1...... and exits #10..then onto the positive of the meter. NEG of
meter goes DIRECTLY to the
B- end of the HV supply. Take is directly to the B- end of the HV caps
if you can at all possible. Don’t do some arrl fubar and run it to the
chassis.
## On my hb amps, I use a HV fuse in series with the 50 ohm glitch
resistor... in series with the B+. In those cases, I use one HV meter
in the HV supply, and a 2nd HV meter in the RF deck itself. If the HV
fuse blows open,
the HV meter in the HV supply will still read 5kv. The HV meter in
the RF deck will read ZERO. This is done for safety purposes. In some
cases, I will use a 3rd box, full of HC caps.... and that box also gets
it’s own HV neter.
later....... Jim VE7RF
Why the heck would anyone use 10 HV resistors? That would look like the
mess
of 1/4W on a Harbach board that I always replace with three 5M Ohmites
anyway.
For 5KV and that meter 5 Ohmite Slim-Mox 1M 7.5KV resistors is all that is
needed. They are 1.25W rated and only $3.90 ea at Mouser. Mount on a
phenolic, and not perf board, and elevated on short phenolic, ceramic, or
other standoffs. The idea is to not have the resistor body on the phenolic
where years of HV will attract a possible conductive path. Perfboard is
more
prone to moisture absorbtion but in a dry area its OK.
Carl
KM1H
### Sure, that will work just fine....and less resistor's required.
With 5 kv applied, the
diss = 5 watts. 5 x 1.25 watts = 6.25 watts. So you are running em at
80% of their
diss rating, which may be a concern.
** Understood but I dont expect someone to be running a 5KV meter at 5KV, in
that case Id configure for 10KV and not have to worry about a new scale (-;
SNIPPED
## I also tried Bill, W6WRT's method, and although it works, I wanted an
HV meter that is
totally independent of EQ resistors. In one of the HV supplies, Oil caps
were used. In the
RF decks, I require a stand alone HV meter.
** Ditto. If Ameritron/Dentron/Heath, etc didnt use that method there must
be something wrong since they wouldnt skip the chance to save a few bucks
(-;
It sounds like some ARRL idea.
More SNIPS
## The large perf boards I bought from mouser were all made from this
green fiberglass material.
They won't absorb moisture at all, I let one of em sit in water to test
for that. I use the same perf boards
to make FWB assemblies. I also used em to make up series 6A10 diode
assy's for bias for GG amps.
Think the ones I used had .080" holes in em, which will take the .060"
leads from 6A10 diodes etc.
## Never had a problem with em since 1990, but they are not cheap.
Phenolic will absorb moisture, too brittle,
has no strength to it, pita.
later........ Jim VE7RF
** But Hammy Hambone wouldnt think of that or want to spend the money, or
even want to be around that much HV. I have a phenolic board with large
diode blocks that was running about 9500VDC in a 60's industrial amp (water
cooled 14KW Pd Amperex triode) and use phenolic in my ~28 yr old HB 2M amp
up to 4KVDC PS with 1N5408's.
Manufactured that way or cut to size and sealed later they will last a long
time.
Carl
KM1H
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