[R-390] Another "Close to Perfect" R-390a

[Dan Merz]

Mark,  I don't think the ageing of the pto that you described is limited to
Collins pto's.  The Cosmos pto in my EAC 390a also required removal of a
full turn to get it back in the proper range.  Time/temperature may be the
enemy.  That's not to say that there may not have been some effort to cure
the problem but 30 odd years is apparently enough to have another type of
pto (non-Collins) show the same symptom.  Dan. 

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Mark Huss
Sent: Wednesday, March 01, 2006 2:19 PM
To: Bonddaleena at aol.com
Cc: R-390 at mailman.qth.net
Subject: Re: [R-390] Another "Close to Perfect" R-390a

According to a conversation I had many years ago with the son of one of the
Engineers that worked on the R-390 and R-390A design, there was indeed
something 'Special' about the Original 'Collins' PTO.  From what I remember,
we had an R-390A with a PTO that was out of adjustment range.  It was a low
serial number PTO made by Collins, the first time I had seen one.  I had
decided to try repairing it as the School was not exactly high on the
priority list for spare parts.  That is when this fellow told me about his
history, and the solution to the problem.  
I.E., take a half turn off the small coil in the PTO.  The cause, according
to him, was the material used for the large coil form.  It changed
dimensions  with age and heat, causing the inductance to change.  He said
his dad told him about it when he joined.  Said that Collins discovered the
problem in the 75A series, but it did not show up until about the middle of
the first year Collins R-390A run since it took years to show up.  They
fixed the problem in the latter half of the Collins run, and all subsequent
PTO's made by other manufacturers.  So yea, it is 'Special' in that it is
one of the worst PTO's you can have.
       As for the bonifidies of this issue, I never met his father, just
what he told me.  However, the solution did work.  And later I heard that
PTO's on the 75A series Collins do have a problem with being out of
adjustment range.  And I never had the problem with any other PTO by other
manufacturers.  If the tale is true, then Motorola also made PTO's before
1957, so they may also have the same problem. 

Bonddaleena at aol.com wrote:

>In a message dated 2/27/2006 12:02:44 AM Eastern  Standard Time, 
>fwbray at mminternet.com writes:
>Just saw another R-390A -- item  5872325416 -- from you know who.
>
>This is an interesting radio, as it is  described as an "improved 
>Motorola version " but bears a Capehart  plate.
>
>Now my question.  Is there anything unique about the PTO in  this radio 
>which is described as "the exceptional Collins PTO which is very  rare 
>to find as they were only usually put in to special one off receivers  
>built to a higher spec receiver for a special purpose" ??  It looks 
>like  the regular R-390A PTO, but maybe I am missing something as I 
>only have  one radio?  I think I know the answer, but I am always 
>willing to  learn something new.
>
>73,
>
>Fred  Bray
>W6WAW
>
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>The way to tell Martyn is lying, is to see if his lips are moving!
> 
> 
>ron (I've been to his 'shack')
> 
>N4UE
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More women than men believe in ghosts, while more men than women believe in
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really great gadgetry.-- Captain Ed --

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