[R-390] Non-Linear PTO

[Forrest Myers]

I had a problem with my Progressitron PTO where it had a bad spot right
around 100khz Where it was suddenly almost 2khz off, depending on the
direction of tuning. Tuning uphill, it was fine. Tuning downhill, it went
bad at about 105khz and got back on track at about 80khz. Took the PTO apart
and found it to be unrepairable due to the sharpness of the change in the
stack at that point.
Decided to get another PTO.
Bought a junker from Fair Radio. When it arrived, I took a look at it and
didn't have much hope. It was very beat up, dented and dirty. Took the outer
can off to see if the dents reached the inner can and found that they
didn't. The shield on Z702 was badly dented and leaning at about a 10 degree
list to port. I took the cans and brackets off and gave them a good washing.
Decided to to some body work on the Z702 can and got it back into fair
shape. Bent the works inside the Z702 can to where they stood straight up
again. Noticed that T701 had never been soldered in! Wonder how it ever
worked reliably. Probably never did. Soldered T701 in. The output co-ax was
in bad shape and was almost cut in two in a few places. Replaced the co-ax.
Made up a test jumper cable and hooked the PTO up to power to see what would
happen. Hooked a frequency counter to the output and fired it up. The PTO
came up without any smoke and was on a reasonable frequency. Turned the
shaft and it seemed to be very stable. Maybe it was going to work! Adjusted
the PTO to put out 3.4550 mhz and powered it down.
Installed the PTO in R-390 a Capehart SN #557, did the end point adjustments
and it's just fine!
The linearity is within spec and seems very stable. Hope it keeps working!
I'm keeping the old Progressitron for a backup but will probably never use
it because of the bad spot in its tuning range.

Keep em glowing,

Forrest Myers
AG4ND
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"Security is mostly a superstition.  It does not exist in nature...
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