[Amps] RE: 4CX250B Screen Supplies

[R.Measures]

On Jul 30, 2004, at 12:32 AM, Ian White, G3SEK wrote:

> Will Matney wrote:
>>
>> "I'd like to make a modest proposal here: how about not feeding a=20
>> "dirty" supply to *either* of the grids?".......... Ian G3SEK
>>
>> Ian, that's exactly the point I'm trying to get across.
>
> Agreed, we're mostly dickering about different ways of saying the same=20=

> thing.
>
>> The only other thing I mentioned was that voice modulation creates=20
>> more IMD than does the two tone test, and by what I've read, we are=20=

>> all in agreement it does.
>>
>
> Again, agreed.
>
> But taking up Peter's point, even a tone spacing as narrow as 30Hz=20
> don't come anywhere close to a realistic test for an amplifier that is=20=

> supposed to be used with human voice modulation.
>
> The nasty feature of real voice signals - ordinary spoken words - is=20=

> that they also contain a *very* strong pulsing VLF component at a=20
> syllable/word rate of only a few Hz.

=F0  Not to mention the additional problem caused when nasty words are=20=

spoken.
>
> This VLF component drags down the power supply, and makes the amp very=20=

> vulnerable to the large 300-3000Hz components that are often happening=20=

> at the same time. No two-tone test can simulate this, and even=20
> three-tone or pulsed two-tone tests are only tinkering with the=20
> problem.
>
> If you want to measure the SSB IMD performance, then the  *only* truly=20=

> valid test signal is... the human voice.
>
> The question is, how to develop a  reproducible voice test?
>
=F0  Virtually everybody has one built-in.  And, as a free added bonus,=20=

it's the very same one that is going to be used on the air.

> Well, a standard voice signal is very easy to generate, in these days=20=

> of digital audio (I'll come back to the question of *whose* standard=20=

> voice).

=F0  But it's not the same one that will be in use on the air.
>
> ....
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org