[Amps] RE: 4CX250B Screen Supplies

[Steve Thompson]

On Sunday 25 July 2004 11:49, R. Measures wrote:

> > If I wind the carrier power up and down, the screen current goes up
> > and down.
> > If I wind the power up and down at 2Hz the screen current goes up and
> > down at
> > 2Hz and the meter needle will follow it. If I wind the carrier power
> > up and
> > down at 1kHz the screen current goes up and down at 1kHz but the meter
> > needle
> > indicates steady 'average' current because it can't follow the
> > changes, not
> > because the current is actually constant. The regulation of the
> > voltage at
> > the audio frequency does matter. It's tricky winding the power control
> > up and
> > down at audio frequencies manually, two tones does it more effectively.
>
>    I agree, Steve.  However, unregulated screen supplies have a filter C
> that is large enough to minimize 100Hz - 120Hz ripple, so that should
> minimize V-out ripple (and IMD) when the load current changes at a
> 1000Hz rate.
Yes, it's possible to fool a two tone test with enough capacitance - but in 
order to approach the results you will get from an electronic regulator, I 
reckon you need a lot more capacitance than most would think to build in, 
maybe 500uF or more.

Cheers,

Steve