[R-390] Cosmos PTO for 390A - newbie - Help requested

[Jim M.]

The PTO shaft passes from the inside to the front outside through a bearing
assembly.  This can collect dried out grease.  A drop or two of light weight
oil may loosen it up a bit.  The "soft detent" feel may be the effect of the
corrector screws (on the corrector disk) rubbing against the spring loaded
slug of the corrector coil (which it should).  You probably wont feel this
when the unit is installed and you tune from the front panel knob.  

I cleaned my PTO by removing the shaft entirely and cleaning out the dried
grease.  BUT----Be careful if you remove the shaft.  The corrector disk
position relative to the unit is critical.  Also if the unit was ever tuned
beyond its range, or there was excessive pressure on the shaft, the
corrector disk can come loose... it is spot welded to the shaft internally.
If you can get relatively good end point alignment, then the calibration
should be acceptable between end points.  Unless it is excessively off, I
wouldn't mess with the screws.  I was a perfectionist with mine, tweaking
each screw against an accurate signal source every 10-20 khz...but it was
literally an all-weekend job.  What's worse is that the screws tend to
interact.  Tweak one and the calibration either side of it may get pulled
off slightly.  Be happy if you are within a few khz across the band.  That's
why they included the dial zero adjust - to correct for inaccuracies.  You
can get better, but be prepared for a long time of tweaking.  Good luck.
Jim N4BE

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Bob Camp
Sent: Thursday, November 22, 2007 11:00 AM
To: Chris Kepus
Cc: R-390 at mailman.qth.net
Subject: Re: [R-390] Cosmos PTO for 390A - newbie - Help requested

Hi

There may be some magical twist / turn / tug / bend combination that  
gets the cover off without unsoldering the leads. The simple answer is  
to unsolder them. You certainly do not want them to break while you  
are working on the rest of the unit.

Electrically all of the PTO's are basically the same. Mechanically  
they can be very different. There were pictures of the insides of a  
Cosmos up on the net a few years back. There also were basic  
instructions on working with the corrector on them.

The PTO was replaced as a unit by the military when it went out. If  
they re-did  correctors it was at some kind of 9th level depot. I  
don't think you will find a lot of PTO alignment stuff in the TM's.  
The Cosmos PTO's exist mostly because of large replacement orders  
placed after the radios were in service.

The PTO should turn under finger pressure. How easy / hard depends on  
a lot of things. In an older unit, you probably have a lot of caked up  
grease inside everything. Once you get that out it should smooth out  
some.

Bob
KB8TQ


On Nov 22, 2007, at 12:47 AM, Chris Kepus wrote:

> All,
>
> This is a bit long but I would really appreciate your taking a  
> look.  I have
> to operate on a PTO, I believe, and this is the first one I've put a  
> hand
> on.....yep....I haven't taken one apart...yet.
>
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