[AMRadio] Modulation of the screen grid

[patrick jankowiak]

I agree completely, unfortunately my laziness is the culprit here. The
plate and screen modulation transformers have no secondary center
taps, I was too lazy to re-do the symbol, that is, I am not very good
at CAD and don't know how to do this properly yet. 

But this is more than worthwhile, I will look into using a different
transformer for the screen, I have several, and one might make a mutch
better match as your calculations clearly show. I think I have a 50W
multimatch around somewhere that would do a better job with the turns
ratio than that big 125W bugger.

Thank you, 
Patrick

> From: "John Coleman, ARS WA5BXO" <wa5bxo at pctechref.com>
> 
> Hi Patrick
>         It looks as though you have made all the right calculations.
> But keep in mind that the purpose of the screen modulation transformer
> is to lower the audio voltage going to the modulator and its design
> impedance is of little importance.  Its turn ratio is of most concern.
> And if I may make two assumptions here then there might be some
> simplification.
>         Assuming that the secondary of the modulation XFMR and the
> screen modulation XFMR have a 50/50 split, then consider starting with a
> lower audio voltage by using the center tap of the modulation XFMR as
> the take off point for the screen audio.  This voltage should be 1/2 of
> the audio voltage of the top point.  Then consider using only half of
> the secondary in the screen modulation XFMR. You can only do this if the
> primary of screen modulation XFMR can handle the higher primary audio
> voltage which will of course be twice as high as before.  The dropping
> resistor is then much smaller and much less heating and loss involved.
> 
>         I took the liberty of recalculation all the parameters for using
> 1/2 of each XFMR secondary which you can view at
> http://wa5bxo.shacknet.nu/HAMPICTURES/mod002.GIF