[R-390] PTO Rebuild - and Core Disaccommodation and other effects

[Bob Camp]

Hi

There is a documented issue with the original Collins PTO design for 
the 390 and 390A. There is an article in one of the mag's about it. The 
dominant issue is mechanical with the coil form, but the material gets 
into the act as well.

At the insistence of Collins engineering I have run more long term 
drift tests on iron core coils than I care to remember. I have never 
found an issue that traces back to core materials in parts made of 
modern powdered iron compositions. Ferrites are a different animal 
entirely. When they are used as a core material there are long term 
issues.

Collins figured this out fairly quickly after the first 390A's came 
out. There are engineering documents somewhere on the topic. I once 
worked for one of the guys who was on the team that fixed the problem. 
They did get it right, the fix went into the R392. There are 392's that 
are significantly older than most 390A's, they run every bit as hot. 
They don't have the PTO problems. The 390A's have been "eating" PTO's 
since the mid 60's. There are documented stories of mountains of dead 
PTO's piling up out behind various depot locations.

The biggest mystery is this - If Collins figured out the problem and 
fixed in time for the R392 - Why did the world keep making the PTO's 
"wrong" for years and years after that? Nobody has ever come up with an 
answer to that one. The government certainly owned the rights to both 
designs. The R390A contractors followed the old formula to the letter, 
and the 392 contractors followed the new formula. It's not like they 
didn't redesign the 390A PTO a couple of times ...

	Strange

		Bob Camp
		KB8TQ


On Apr 7, 2005, at 6:20 PM, Cecil Acuff wrote:

> So now we need to take into consideration the "Half Life" of the PTO 
> cores as well as the meters and mechanical filters....
>
> Interesting..
>
> Cecil..
> ----- Original Message ----- From: "John KA1XC" <tetrode at comcast.net>
> To: "R-390 reflector" <r-390 at mailman.qth.net>
> Sent: Thursday, April 07, 2005 4:56 PM
> Subject: Re: [R-390] PTO Rebuild - and Core Disaccommodation and other 
> effects
>