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Measures, Orr, et al have presented excellent information concerning the =
great importance of correct PA fil voltage. Being mostly a CW op, my =
current peaks are much lower than those in SSB mode. Therefore, I have =
lowered the fil voltage on my pair of 3-500Zs the recommended amount, =
and they have rewarded me with faithful, extended service life.
However, the methods proposed in these discussions are rather extreme or =
awkward. My method is simply to install the dropping resistor in the =
fil xfmr primary, instead of the more critical secondary. It does =
require that your amp has a separate fil xfmr of course. The values =
needed for primary resistors are very much more commonplace than those =
in the secondary.
When measuring fil voltage it is important to use the proper type of =
meter. The waveshape is often distorted enough so that it becomes a =
consideration how your meter responds to the average voltage. The very =
best type is the iron vane AC meter. These are sometimes available used =
from industrial sources. I have used iron vanes with mirrored scales, =
and some have typical accuracies of 0.1 percent at 3/4 scale. Iron =
vane AC meters inherently average waveform distortion to a near perfect =
degree. Anyway, keep an eye out for them.
73, K6XK/0 =20
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<DIV><FONT color=3D#000000 size=3D2>Measures, Orr, et al have presented =
excellent=20
information concerning the great importance of correct PA fil voltage. =
Being=20
mostly a CW op, my current peaks are much lower than those in SSB mode.=20
Therefore, I have lowered the fil voltage on my pair of 3-500Zs the =
recommended=20
amount, and they have rewarded me with faithful, extended service=20
life.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>However, the methods proposed in =
these=20
discussions are rather extreme or awkward. My method is simply to =
install=20
the dropping resistor in the fil xfmr primary, instead of the more =
critical=20
secondary. It does require that your amp has a separate fil xfmr of =
course. The=20
values needed for primary resistors are very much more commonplace than =
those in=20
the secondary.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>When measuring fil voltage it is =
important to=20
use the proper type of meter. The waveshape is often distorted enough so =
that it=20
becomes a consideration how your meter responds to the average voltage. =
The very=20
best type is the iron vane AC meter. These are sometimes available used =
from=20
industrial sources. I have used iron vanes with mirrored scales, and =
some =20
have typical accuracies of 0.1 percent at 3/4 scale. Iron vane AC =
meters=20
inherently average waveform distortion to a near perfect degree. =
Anyway,=20
keep an eye out for them.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>73, =20
K6XK/0 </FONT></DIV></BODY></HTML>
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