----- Original Message -----
From: "Glen Zook" <gzook@yahoo.com>
To: <amps@contesting.com>; <rfamplifiers@yahoogroups.com>; "Steve Flood"
<kk7uv@bresnan.net>
Sent: Wednesday, December 17, 2008 9:17 PM
Subject: Re: [Amps] amp p/s metering
> For accuracy I definitely would use some 1% to 5% resistors in a
> separate multiplier string.
Use considerably higher values in the multiplier string so that they
don't act as bleeder resistors. Using something like a 9 megohm
resistor in series with a 1 megohm would give a 10:1 voltage ratio if
the voltmeter has a high ohms per volt. I know, this is not exact.
But, close enough for government work.
>
> Most bleeder resistors don't have high tolerances so they can vary
> quite a bit in relation to each other.
I guess you havent checked out 5-10W resistors in a LONG time. Many are
rated at 5% tolerance and most measure withinn 2% thanks to modern
manufacturing processes.
Your suggestion makes no sense unless money is no object....have you
priced a 9M precision resistor rated at several KV?
If ultimate accuracy is desired on the cheap, buy extra bleeders, match
to within 1% , then take the meter line off the top of the last cap in
the string and finish the divider based on the meter sensitivity, this
will require several megohms to complete. You are now at a relatively
low voltage and can finish off with common 1/2W film resistors.The
SB-220 used 14 M in the string.
Carl
KM1H
>
> Glen, K9STH
>
> Website: http://k9sth.com
>
>
> --- On Wed, 12/17/08, Steve Flood <kk7uv@bresnan.net> wrote:
>
> From: Steve Flood <kk7uv@bresnan.net>
>
> Is it 'better' to meter the high voltage at the bottom of a bleeder
> string (I have 8 100k resistors in a SB-220-style power supply), or is
> it 'better' to build a seperate multiplier string between B+ and B-
> for the meter?
>
>
>
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