[AMRadio] High level modulation of tetrodes


John E. Coleman (ARS WA5BXO) wa5bxo2005 at pctechref.com
Wed Sep 28 10:52:51 EDT 2005


	I like the way he returned the audio load back to the main supply
eliminating the need for the extra capacitor.  As you pointed out the two
resistors are in parallel as for as DC to the screen is concerned so if a
fellow was modifying and existing circuit he would need to change the
existing screen resistor as well as adding one in order to keep the DC
voltages the same.  The high frequency compensation capacitor is also a very
good idea to compensate for the screen bypass capacitor side effect of
rolling off the highs.

John,
WA5BXO

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Bob Bruhns
Sent: Tuesday, September 27, 2005 9:13 PM
To: Discussion of AM Radio
Subject: Re: [AMRadio] High level modulation of tetrodes

For screen self-modulation, probably the higher the series impedance, the
better.  So an inductor in series with a resistor in the
screen circuit would be better than either the resistor or the inductor
alone.

WA1KNX Dino suggested a resistive voltage divider from modulated plate B+ to
unmodulated plate B+ feeding the screen.  The ratio of
resistances was about 6 to 4, for about 40% modulation.  The screen would
see 40% modulated plate B+ coming through a resistance
equal to 1/((1/R1)+(1/R2)).  A compensating capacitor was included to tweak
the screen modulation at higher audio frequencies.
http://www.amwindow.org/tech/htm/scrnmod.htm

   Bacon, WA3WDR








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