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Re: [Amps] Small transformer evaluation

To: amps@contesting.com
Subject: Re: [Amps] Small transformer evaluation
From: Vic K2VCO <k2vco.vic@gmail.com>
Date: Sat, 01 Sep 2012 14:20:58 -0700
List-post: <amps@contesting.com">mailto:amps@contesting.com>
It's going to feed a transistor regulator. I'm sure it will be a capacitor filter because of the voltage.

On 9/1/2012 1:55 PM, Bill, W6WRT wrote:
ORIGINAL MESSAGE:
On Sat, 01 Sep 2012 13:37:10 -0700, Vic wrote:

Some of you will remember that I was wondering about utilizing a small Philco 
power
transformer (model 45-7011-7) for a screen supply. It puts out 380-0-380 vac 
plus 5 and 6
v for filaments. I have hooked it up jn a full-wave ct circuit feeding a 
choke-input
filter and 20 uf capacitor. It is feeding a 4300 ohm 50w resistor for a load.

REPLY:
You should not use a choke input filter for a screen supply except for constant
carrier modes such as FM or RTTY. When the screen current varies as with SSB and
CW, the varying current through the choke will cause voltage spikes and slumps.
You can easily see this with an oscilloscope. The screen voltage should always
be constant.

A simple capacitor-only filter is best. And it will solve your low-voltage
issue.

73, Bill W6WRT
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--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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