[R-390] COSMOS PTO Calibration

[Pete Williams]

List.. g'day.
Calibration /adjustment of the COSMOS pto has been covered fairly
extensively and removal of one turn from the endpoint coil appears in most
cases to allow correct 10 turn spread.
However , having decided to check out one of my spares , I found the
situation where one turn off the  coil and adjustment of the slug did not
bring the  end points within spec--- about 5 kHz low.
Reasoning that one or more of the capacitor components had  gone high, I
snipped out one of the miniature 10 pf across the whole inductance .
Result is that the PTO endpoints, after processing, now accurately set and
linearity spot on.
No doubt the purists will take me to task on this as the 2 miniature caps in
parallel: one is  N750 and the other NPO.... I could not identify which one
I removed . The posibility too ,is that the large  screw mounted 370 pf  has
changed value cannot be  discounted, but the effort on checking this  and
even getting a replacement made the  previous option a more viable
proposition.
Stability  before  and  after appears not to have  changed, and heat
treatment from  room temp. at 50 F to 90F only changed the freq. by a max of
10 Hz.
The testing was done with a maximum of  convenience...on the bench using a 2
voltage regulated variable supply giving the 150 and 250V required and  the
output loading to a frequency counter.

Any comment appreciated together with caveats on the empirical procedures.
No doubt there is the possibility that if unstable the   cap or whatever
might revert to normality or worse--- but them's the breaks !

Cheers 
Pete
 



 Pete D.Williams
jupete at bigpond.net.au
METUNG 3904 AUSTRALIA