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My experience with several commercial amps has driven home one serious =
design weakness common to most brands. This is severe PA tank circuit =
resonance drift caused by heat instability in the fixed padder caps used =
to tune the tanks down to the low bands (most often 80 and 160 meters).
Transmitting ceramics simply do not have the stability to be =
incorporated in this demanding application. During "heavy duty" =
operating, the heat given off by the PA tubes in the tank compartment =
causes violent drift in the ceramic caps. This in turn detunes the tank, =
causing more plate dissipation to occur which further heats the caps, =
and so on. In other words, a vicious, destructive cycle exists which is =
absolutely objectionable. I believe some heating is also internal to the =
caps themselves, generated by the dielectric in this high RF current =
service.
I have had to replace all such caps in my amps with their stable =
counterparts: namely, xmitting micas. I realize they are hard to find =
and are expensive and take up more space. But they are absolutely =
necessary--unless the variables themselves are "big" enough to tune all =
the way to 160 meters. (Also not cheap, I know).
We are willing to pay more; please refrain from using ceramics in the =
Titan II. And make known this good feature in your advertisements.
Thanks & 73, Roy K6XK
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<DIV><FONT color=3D#000000 size=3D2>My experience with several =
commercial amps =20
has driven home one serious design weakness common to most brands. This =
is=20
severe PA tank circuit resonance <U>drift</U> caused by heat instability =
in the=20
fixed padder caps used to tune the tanks down to the low bands (most =
often 80=20
and 160 meters).</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>Transmitting <U>ceramics</U> simply =
do not have=20
the stability to be incorporated in this demanding application. During=20
"heavy duty" operating, the heat given off by the PA tubes in =
the tank=20
compartment causes violent drift in the ceramic caps. This in turn =
detunes the=20
tank, causing more plate dissipation to occur which further heats the =
caps, and=20
so on. In other words, a vicious, destructive cycle exists which is =
absolutely=20
objectionable. I believe some heating is also internal to the caps =
themselves,=20
generated by the dielectric in this high RF current =
service.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>I have had to replace all such caps =
in my amps=20
with their stable counterparts: namely, xmitting micas. I realize they =
are hard=20
to find and are expensive and take up more space. But they are =
absolutely=20
necessary--unless the variables themselves are "big" enough to =
tune=20
all the way to 160 meters. (Also not cheap, I know).</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>We are willing to pay more; please =
refrain from=20
using ceramics in the Titan II. And make known this good feature =
in your=20
advertisements.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>Thanks & =
73, =20
Roy K6XK</FONT></DIV></BODY></HTML>
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