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Re: [Amps] 8877 Grid Connection DC or Not

Subject: Re: [Amps] 8877 Grid Connection DC or Not
From: Gerald Williamson via Amps <>
Date: Wed, 30 Nov 2016 17:15:30 -0500
List-post: <">>
I have used a non optical scheme at 9KV for a twt power supply. The hv is  
fed through a 100 ohm resistor, 100w in my case. The current through the  
resistor is about 500 mA so the voltage drop is 50v. On both ends of the  
resistor there is a 1000 to 1 voltage divider that results in about 9 volts to  
ground on one and about 9.05 volts on the other. A meter with a hand picked  
multiplier in series is connected between the two dividers. The series 
resistor  was picked to make the  meter read  half scale which corresponds to  
the 500 mA   of current flow from the power supply. I am thinking the  meter 
movement is 100 microamperes but that is not critical. The meter circuit  
resistance is on the order of 10K ohms and that will cause a voltage drop at 
the  output of the dividers. This is why the series resistor is hand selected 
as a  calculation is somewhat complicated. The easiest method is using a 
series  potentiometer and simply adjust it until the meter reads correctly. 
The power  supply voltage is read from one of the dividers to ground. Reading 
at 9v is  a bunch safer than reading at 9 KV. 
The only downside is the need build two voltage dividers using enough  
series resistors to stay within the voltage rating of the resistors Mine was  
wired on  phenolic perfboards.
Gerald K5GW
In a message dated 11/30/2016 1:01:44 P.M. Central Standard Time, writes:

Hi  Jim,
Ah... the unknown factor.

You could  include an (optically?) isolated plate current sensor and then 
do the math and  metering at low voltage.

73 & Good morning,
Marv  WC6W

On  Tue, 11/29/16, Jim W7RY <> wrote:

Subject: Re:  [Amps] 8877 Grid Connection DC or Not
To: "Radio WC6W"  <>, "AMPS" <>
Date:  Tuesday, November 29, 2016, 3:37 PM

Marv... Because this will
be a  single power supply and multiple RF deck (5 
or 6 of them) amplifier system  for a contest
station.  I don’t want to use 
relays as  high voltage switches.

Metering plate current is easy. Simply put  the
plate current meter (set back 
from the
front panel for safety)  in series with the HV on the RF

That’s  why.

Jim W7RY

-----Original Message-----  
From: Radio WC6W
Sent: Tuesday,
November 29, 2016 11:35 AM
To:  Jim W7RY ;
Subject: Re: [Amps] 8877 Grid
Connection DC or  Not

Hi Jim,
Why not
leave the grid grounded  but, just measure the cathode and
currents then subtract to  calculate
the grid current?

73 &
Good  morning,
Marv  WC6W

On  Mon, 11/28/16, Jim W7RY <>

Subject:  [Amps] 8877
Grid Connection DC or Not
"AMPS"  <>
Date: Monday, November 28, 2016, 7:00  PM

Has anyone run the grid of an
not connected to ground as  far as DC is

I really need to
meter the grid current  by bypassing the
to ground with capacitors and several 10 ohm  resistors
in order to meter grid current. Metering grid
current by  the
CT of the filament
transformer, and the – of the  power
cant be done. Because the power supply – is
directly  grounded.

Anyone had luck doing this?

Thanks 73
Jim  W7RY
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