Hi Phil,
The amplifiers I was working on had 4 final PA xsistors. All four were
driven from a single power divider and their collectors fed a single
power combiner AND all four had a common bias. They did not have
independant bias adustments for each pair. The transistors were probably
each operated in quadrature, using phasing lines and transformers on the
PA PC board. That is easy to do in an amplifier that only covers a
fraction of an octave of frequency response, and not so easy in an
amplifier that covers four octaves as the Hercules II does. So the
Hercules II uses transformers to feed each pair of PA xsistors in
opposite phase, but not quads of xsistors in four phases. So I can see
how your recomendation to change only the failed transistor(s) and their
mate(s) is a probably good advice for the Hercules II.
DE N6KB
Phil Chambley, Sr. wrote:
Just to keep the record straight...I did not suggest replacing only the one
that went bad, but also its mate in the p-p amplifier as well, being mindful
that they should be matched and in the same beta group as the other six.
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