[R-390] PTO Rebuild?

[Roy Morgan]

At 10:03 PM 4/4/2005, Barry wrote:
>Thanks to all for the PTO links.  Apparently mine is not a Cosmos.  In fact,
>it's a "no-name".  It does not have the extra opening for the corrector
>stack screws, so I assume I'm looking at one that will require shimming.

May I clarify a bit?

The Cosmos PTO uses a flexible disk with a series of adjustment screws to 
make the frequency correction.  These screws are adjusted from the outside 
of the PTO case.

The other, "standard" design uses a stack of corrector plates and a 
corrector follower bearing to make the frequency correction. These plates 
are adjusted inside the PTO case by loosening the clamp screw and moving 
the plate "up or down" with respect to the frame.  The clamp screw holds 
all the plates in position. Provision is made so that adjustments to one 
plate do not move the ones on either side of it.

>I'll have to check the linearity, and if it's off far enough, then it will
>be "stand back, Jim, I'm goin' in!"

Congratulations on having a stout heart.  No doubt you'll have a 
success.  As I understand it, adjusting the linearity a normal-design, 
corrector stack PTO involves the following points:

  - The PTO cover must be removed, either once being replaced by a cover 
with an access slit cut in it, and a hole to get at the locking screw, or 
removed and replaced each time a correction or series of corrections is 
made to a plate or plates.
  - a jig is very useful so the PTO does not need to be re-installed in a 
radio each time adjustments are made.  The jig would allow setting the 
shaft to close rotational tolerances, supply power to the PTO, and perhaps 
provide a proper load for the oscillator output.
  - A frequency meter is extremely useful
  - mechanical means of moving each plate, and only one plate, a known 
amount is very useful.
  - likely a computer spreadsheet or paper table would be most useful to 
correlate changes in set point frequencies with the mechanical movement 
made to each plate, in thousandths of an inch or millimeters or whatever.

Likely, all this was done at the factory with the PTO brought up to oven 
temperature.

Roy

- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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