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
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