[Amps] RE: 4CX250B Screen Supplies

[R.Measures]

On Jul 26, 2004, at 1:27 AM, Steve Thompson wrote:

> 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.
>
Steve -- For the current 8171 project, I'm going to start with 140µF on 
the output side of a 1500V resonant-choke supply. If that does not get 
the job done satisfactorily, I will go with something better.
end
> Cheers,
>
> Steve
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>
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org