[R-390] Adjusting Linearity Stack Collins PTO

[David Wise]

Shoot, I forgot another thing.  If you let
your thumbnails grow out a bit, if you
hold the open PTO a certain way, you can
push individual chips from side to side
very precisely between them.

73,
Dave Wise

> -----Original Message-----
> From: David Wise=20
> Sent: Friday, December 27, 2002 3:18 PM
> To: Dave or Debbie Metz; r-390@mailman.qth.net
> Subject: RE: [R-390] Adjusting Linearity Stack Collins PTO
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> I forgot to mention part of my procedure.  I didn't
> cut any holes.  I took off the outer can and the oven.
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> Warm it up a few hours.
> Take data.
> Power down.
> Remove.
> Disassemble.
> Adjust.
> Reassemble.
> Replace.
> Power up.
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> 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.
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> 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.
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> 73,
> Dave Wise
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> > -----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
> >=20
> >=20
> > 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,
> >=20
> > Right you are on the difference between collins and Cosmos.
> >=20
> > 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:
> >=20
> > 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.
> >=20
> > 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=20
> 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.
> >=20
> > 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.
> >=20
> > 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.
> >=20
> > 73's
> > dave
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> >=20
> >=20
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