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How linear is the PTO (permeability tuned
oscillator, it is ganged to the tuning knob, along with the gear train for the IF)?
In other words, on a given band, is it off by the same amount at the top,
middle, and bottom of the range? Is the error constant in a given band,
just different depending on the band? If so, you are in good shape. The radio is
essentially a tuned IF with fixed crystal-controlled converters in the front end. As
long as the PTO is linear, a good alignment should fix her right up. If
the PTO is off, it can be fixed, providing that it is still in the
adjustment range. Special tools to adjust and lock the trimmers in the PTO are
required, and it is a bit tedious to do, but not especially hard. Just time consuming,
making small changes and checking the linearity across the dial.
I did one 75A4, and I remember it took all day doing the
adjust/check/readjust/recheck thing. But it came out OK in the end. If the PTO is out of
adjustment range, it will have to go to the factory, if they still do that
sort of thing, or replace it with another PTO. I am going to guess that she just needs an
alignment, since I think you are saying that she is off differing amounts on each
band. The lowest band uses just the IF, so that is a good indication as to the
linearity of the PTO itself. I can't remember the links at the moment, but there
are a lot of good web pages detailing the steps to align the radio and the
PTO. Does yours have the meters still installed (signal
strength and line-level)? Rick |