[Amps] Small transformer evaluation

[Bill, W6WRT]

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