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.
73,
Gerald K5GW
In a message dated 11/30/2016 1:01:44 P.M. Central Standard Time,
amps@contesting.com 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
http://qsl.net/wc6w/
--------------------------------------------
On Tue, 11/29/16, Jim W7RY <jimw7ry@gmail.com> wrote:
Subject: Re: [Amps] 8877 Grid Connection DC or Not
To: "Radio WC6W" <wc6w_amps@yahoo.com>, "AMPS" <amps@contesting.com>
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
vacuum
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
deck.
That’s why.
Thanks
73
Jim W7RY
-----Original Message-----
From: Radio WC6W
Sent: Tuesday,
November 29, 2016 11:35 AM
To: Jim W7RY ;
AMPS
Subject: Re: [Amps] 8877 Grid
Connection DC or Not
Hi Jim,
Why not
leave the grid grounded but, just measure the cathode and
plate
currents then subtract to calculate
the grid current?
73 &
Good morning,
Marv WC6W
http://qsl.net/wc6w/
--------------------------------------------
On Mon, 11/28/16, Jim W7RY <jimw7ry@gmail.com>
wrote:
Subject: [Amps] 8877
Grid Connection DC or Not
To:
"AMPS" <amps@contesting.com>
Date: Monday, November 28, 2016, 7:00 PM
Has anyone run the grid of an
8877
not connected to ground as far as DC is
concerned?
I really need to
meter the grid current by bypassing the
grid
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
supply
cant be done. Because the power supply – is
directly grounded.
Anyone had luck doing this?
Thanks 73
Jim W7RY
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