[R-390] Adjusting Linearity Stack Collins PTO

[Dave or Debbie Metz]

At 09:04 AM 12/27/2002 -0500, Jim M. wrote:
>Thanks...I found this link, and also some references to Electric Radio
>articles, doing a Google.com search (an amazing thig).  Note:  The PTO
>alignment discussions on the r390a.com page appear to discuss only the
>Cosmos manufactured PTO.  The linearity adjustment for Collins mfgd PTOs
>is considerabily different.
>
>http://groups.yahoo.com/group/r-390/message/4718

Jim,

Right you are on the difference between collins and Cosmos.

A long time ago, I tried it and had limited success on a PTO that was out 
6-8 kc with a procedure that went something like this:

Take a junker PTO and cut a slit in the inner can above the camstack about 
a 1/4" wide to allow you to insert a piece of insulated something to push 
on the cam stack just above the roller.  Then, adjust the tightening screw 
so that you can move the stack. First, you need to find the worst 
offset  from end to end such that you are only going to push the stack down 
to either increase or decrease the freq. ( could never quite figure out the 
way to pull the stack up to go the opposite direction in frequency.)  Then, 
mount the pto into the receiver with only the inner slotted can and push 
down at each 25khz increment to either raise (or lower, I cannot remember). 
the freq to the desired freq. I only used the inner can with the slit. This 
creates a bit of a problem because you have no rear mount so you have to 
brace it somehow. You should "T" in a counter to measure the freq with a 
counter. Remembering the PTO goes from 2.455--3.455 inversely as the freq 
is acending you need to set up a chart to know what is the desired PTO freq 
@ each 25khz indicated.

I am sorry for the lack of detail but it's been a few years and I forgot 
the details.  I am sure there must be a better way. However, I was  not 
able to figure a way to adjust the camstack short of pulling the PTO 
hundreds of times with a trial and error method. I seriously doubt that 
Collins did anything trial and error.  I am so in awe of the engineering of 
this setup. What a sophisticated way to linearize a very delicate oscillator.

I know that there has been a lot of talk about the PTO manufacturers here 
on the list but a long time ago I had a conversation with Paul Zechinno  at 
Mil Spec Communications, (Not Rick Mish) and he was less than complimentary 
on Cosmos compared to the Collins PTO's. He had years of experience with 
these and felt that the Cosmos was probably fine when it left the factory 
but would not weather the years like the Collins units in the non A 390's.

However, bottom line: Don't do it!  If you  have a PTO  within one or two 
KC, you have NO problem. It never was perfect and I doubt seriously that 
you can achieve anything better.

73's
dave