[Amps] plate voltage meter shunt

[Jim Thomson]

Date: Sat, 03 Nov 2012 23:31:34 -0700
From: Bill Turner <dezrat1242 at yahoo.com>
To: Amps <amps at contesting.com>
Subject: Re: [Amps] plate voltage meter shunt
Message-ID: <h72c98t1tn304d2u4bbt04ff26qgn9rpfp at 4ax.com>
Content-Type: text/plain; charset=us-ascii

Another advantage of using the bleeder string instead of a separate multiplier
resistor is you monitor two parameters with one circuit.

1. Not only do you save money on a separate and expensive HV resistor.
but 
2. You are also monitoring the health of your bleeder string. If you see an
unexpected change in the indicated plate voltage, that might be a real change or
it might indicate a resistor in the bleeder string is failing. Either way,
troubleshooting is called for. 

If it's a bleeder resistor failing, you might catch it in time to prevent damage
to your filter caps. Otherwise, you'd never know until it's too late. 

Two for the price of one and cheaper besides. That's always good design
practice. 

73, Bill W6WRT

##  If you want the BEST 100k 3 watt MOF EQ, 1% TOL resistor that’s  out there,
it’s  made by VISHAY,  CPF3100K00FHB14 

##  Vishay Cust pn #  71-CPF3-F-100K-T2

##  They come in box’s  of 100.  I bought 300 of em for various projects.  Tony King
put me onto these things....available at Mouser.  I checked all 300 of em..and all 
300 of em were exactly  200 ohms on the low side..= .2% tol.   For an eq resistor,
the value itself is no big deal, anything from 90-110K is fine.   What you want is for
them to all be the same. 

##  with these beauties, the V drop across each cap in a series string will be the same. 
IE: the v drop across each cap on a 2650 vdc supply, like in my L4B supplies,  will be
exactly 331.25 volts dead on.   You couldn’t ask for a better EQ resistor.   Tony put
me onto these vishay types, since he was fed up with having to play “match up”  all the
time with the 5%  tol types... = pita.   

##  Now although these things are rated at 1%  Tolerance..which implies +/-  1%
they are in fact  -.2 % tol.   Zero problems with em for years now.  The typ bleeder current
drawn through em will more than swamp out the leakage current of quality caps.  With the
caps, I hand match them up.   I measure the esr of each one, and also the uf. 

##  On an expensive hb amp, or a modified commercial amp,  I don’t have the patience for 
cutting corner’s anywhere.  Just do it right the 1st time. 

##  Sure, Bill’s idea will work, using the last cap at the cold end of the string.  As long as the
calibration pot, etc, does not go open, etc.  Otherwise the last cap at the cold end will then 
have the FULL  B+  voltage across it, resulting  in that cap exploding like a grenade. 

##  the same thing will happen to any of the other caps in the string if  any of the 100 K resistors
ever opened up......  hence use good quality parts to begin with.    

Jim  VE7RF