[Amps] plate voltage meter shunt

[Carl]

Subject: Re: [Amps] plate voltage meter shunt


>
>
> -----Original Message----- 
> From: Carl
> Sent: Sunday, November 04, 2012 4:29 AM
> To: Jim Thomson ; amps at contesting.com
> Subject: Re: [Amps] plate voltage meter shunt
>
>
>
>
>> 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
>
> ###  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