"kc7fys" wrote in message
oups.com...
Hello,
My grandpa has this nice old boat anchor in his basement.
A prototype
from when he built them at Collins. He may go QRT in the
next few
years, and wants me to have the rig running and up. We
need this
capacitor--he says it drifts badly without it.
Where should I check for it? Anybody familiar with this
exciter?
www.flickr.com/photos/jonathancharles/sets and you'll see
photos of it
there.
Best 73,
Jonathan 7J1AWL/KC7FYS

There is a schematic of the 70E as part of the schematic
for the 32V-3 which I got off the Collins Org site at:
http://www.collinsradio.org/html/manuals.html
While the component values are shown they are not listed
in the parts list, probably because the PTO was serviced by
replacing it as a unit. However, the circuit layout may be
useful. The 710uuf cap appears to be the main resonating
capacitor in the oscillator tank. There is also a variable
capacitor and a cap marked with an asterisk with a note that
it is chosen at the factory. There is no indication of what
it is chosen for or its approximate value. It would be
surprizing if the 710uuf cap is a temperature compensating
cap because of it is the predominant capacitance in the
circuit but you never know. It may be that someone at this
site knows more about the construction of the 70 series
PTOs.
I had always heard that PTOs would drift if the seal was
broken. Evidently they were filled with dry air. Some at
least have dessicators in them. Evidently low humidity is
important to their operation.
I would explore the Collinsradio Org site, maybe you can
find something definite there.


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Richard Knoppow
Los Angeles, CA, USA