[R-390] Adjusting Linearity Stack Collins PTO

[David Wise]

I forgot to mention part of my procedure.  I didn't
cut any holes.  I took off the outer can and the oven.

Warm it up a few hours.
Take data.
Power down.
Remove.
Disassemble.
Adjust.
Reassemble.
Replace.
Power up.

Repeat until you're sick of it :-)  I got mine to about
100Hz, but that's down in the noise compared to endpoint
drift, and I doubt it's still that good.

I got a Cosmos unit at a swap meet last summer.  I'm
looking forward to getting into it sometime.  It'll
be a breeze compared to the Collins.

73,
Dave Wise

> -----Original Message-----
> From: Dave or Debbie Metz [mailto:metzd@intelos.net]
> Sent: Friday, December 27, 2002 3:01 PM
> To: r-390@mailman.qth.net
> Subject: Re: [R-390] Adjusting Linearity Stack Collins PTO
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> At 09:04 AM 12/27/2002 -0500, Jim M. wrote:
> >Thanks...I found this link, and also some references to=20
> Electric Radio
> >articles, doing a Google.com search (an amazing thig). =20
> Note:  The PTO
> >alignment discussions on the r390a.com page appear to=20
> discuss only the
> >Cosmos manufactured PTO.  The linearity adjustment for=20
> Collins mfgd PTOs
> >is considerabily different.
> >
> >http://groups.yahoo.com/group/r-390/message/4718
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> Jim,
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> Right you are on the difference between collins and Cosmos.
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> A long time ago, I tried it and had limited success on a PTO=20
> that was out=20
> 6-8 kc with a procedure that went something like this:
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> Take a junker PTO and cut a slit in the inner can above the=20
> camstack about=20
> a 1/4" wide to allow you to insert a piece of insulated=20
> something to push=20
> on the cam stack just above the roller.  Then, adjust the=20
> tightening screw=20
> so that you can move the stack. First, you need to find the worst=20
> offset  from end to end such that you are only going to push=20
> the stack down=20
> to either increase or decrease the freq. ( could never quite=20
> figure out the=20
> way to pull the stack up to go the opposite direction in=20
> frequency.)  Then,=20
> mount the pto into the receiver with only the inner slotted=20
> can and push=20
> down at each 25khz increment to either raise (or lower, I=20
> cannot remember).=20
> the freq to the desired freq. I only used the inner can with=20
> the slit. This=20
> creates a bit of a problem because you have no rear mount so=20
> you have to=20
> brace it somehow. You should "T" in a counter to measure the=20
> freq with a=20
> counter. Remembering the PTO goes from 2.455--3.455 inversely=20
> as the freq=20
> is acending you need to set up a chart to know what is the=20
> desired PTO freq=20
> @ each 25khz indicated.
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> I am sorry for the lack of detail but it's been a few years=20
> and I forgot=20
> the details.  I am sure there must be a better way. However,=20
> I was  not=20
> able to figure a way to adjust the camstack short of pulling the PTO=20
> hundreds of times with a trial and error method. I seriously=20
> doubt that=20
> Collins did anything trial and error.  I am so in awe of the=20
> engineering of=20
> this setup. What a sophisticated way to linearize a very=20
> delicate oscillator.
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> I know that there has been a lot of talk about the PTO=20
> manufacturers here=20
> on the list but a long time ago I had a conversation with=20
> Paul Zechinno  at=20
> Mil Spec Communications, (Not Rick Mish) and he was less than=20
> complimentary=20
> on Cosmos compared to the Collins PTO's. He had years of=20
> experience with=20
> these and felt that the Cosmos was probably fine when it left=20
> the factory=20
> but would not weather the years like the Collins units in the=20
> non A 390's.
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> However, bottom line: Don't do it!  If you  have a PTO =20
> within one or two=20
> KC, you have NO problem. It never was perfect and I doubt=20
> seriously that=20
> you can achieve anything better.
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> 73's
> dave
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