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
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of patrick jankowiak
Sent: Sunday, November 30, 2003 1:39 AM
To: [email protected]
Subject: [AMRadio] Modulation of the screen grid
Would anyone mind looking over the schematic at the web page below and
see if I am on the right track to modulate the G2 voltage of a 4-1000?
This should provide the 250 volt peak voltage necessary for the screen
grid, and then I won't have to rely on using just a choke from the
screen supply or a dropping resistor.
Basically I plan to use a smaller mod xfmr to couple some of the
modulated plate voltage to the screen.
Maybe I have some mistakes in the parts or signal level values, but I
think it should be right.
Thanks in advance,
Patrick
http://208.190.133.201/mod001.gif
