[Amps] plate voltage meter shunt

[Carl]

> Date: Sat, 3 Nov 2012 14:15:44 -0700 (PDT)
> From: Douglas Johnson <w9iix1 at yahoo.com>
> To: AMPS <amps at 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