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Author Topic: Any 70K-2 Collins PTO rebuilders out there?  (Read 359 times)

N6AF

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Any 70K-2 Collins PTO rebuilders out there?
« on: October 22, 2021, 09:10:58 AM »

My recently purchased KWM-2 has a PTO instability issue which I'm sure is due to one capacitor.  After dissecting and replacing one suspect cap in it I have changed the acronym from PTO to PITA !

It still has an issue wherein about once every 10 operating sessions it will a) suddenly jump freq about 22 kHz and b) the tracking inaccuracy degrades to about 6 kHz over 200 kHz from the usual less than 1 kHz over 200 kHz.  I was pretty certain it was the 1000 pF cap C302 but nope, changing that didn't clear it.

So after my 'fun' experience of working on the PITA once already, can anyone recommend a PTO re-builder?  Yes, the laziness factor is kicking in on this one.

Thanks 73 N6AF Chuck
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N4UE

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Re: Any 70K-2 Collins PTO rebuilders out there?
« Reply #1 on: October 22, 2021, 10:18:10 AM »

Hi Chuck. Go to the 'Reviews' section here and search for K2LRC, Peter. I have a review in there from 2015.
Peter cane to my aid when a gust of wind from an open shop door scrambled all the 'guts' of my 75S-3 PTO all over my workbench. All the parts were laid out in order on a sheet of paper.
Peter did a fantastic job!

ron
N4UE
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VK6HP

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Re: Any 70K-2 Collins PTO rebuilders out there?
« Reply #2 on: October 22, 2021, 07:28:15 PM »

One good source of guidance if you're up to one more go at it (with links to several Collins Collectors Association (CCA) articles on PTO rebuilding) is:

http://www.collinsradio.org/pto-specification-data/

Stability issues and relevant rebuilding tips are well-covered in http://www.collinsradio.org/70k-2-stability-service/ , which is also linked via the earlier URL.

You may also want to take a look at Don Jackson's (W5QN) article "PTO Frequency Tracking" in the CCA "Signal" for Q2 2021.  Like all of Don's articles it's a good bit of engineering science linked to real-world experience.  The article has very useful insights into S-line PTO design and construction.

73, Peter.
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W9GB

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Re: Any 70K-2 Collins PTO rebuilders out there?
« Reply #3 on: November 03, 2021, 09:00:08 AM »

A Collins 70K-2 PTO Repair Story
by Ernst F. Schroeder, DJ7HS
https://www.qsl.net/dj7hs/70K-2_PTO_repair.htm

Another Collins 70K-2 PTO Repair Story
by Ernst F. Schroeder, DJ7HS
https://www.qsl.net/dj7hs/another_70K-2_PTO_repair.htm

Collins 70-K2 PTO Service Adventures (good start)
by Jim Miller N4BE
http://www.collinsradio.org/70k-2-stability-service/

Collins 70K-2 PTO Lubrication & Assembly
by Paul, W9AC
http://www.collinsradio.org/70k-2-pto-lubrication-assembly/
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W9AC

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Re: Any 70K-2 Collins PTO rebuilders out there?
« Reply #4 on: November 04, 2021, 07:47:29 AM »

For the sake of completeness, here's another article from Dick, K5IU.  Apart from Don, W5QN, Dick has probably studied the theory of operation as much as any of the original Collins designers. 

http://collinsradio.org/Signal/newsletters/Issue%2067%203rd%20Quarter%20of%2012.pdf

Anyone who plans on keeping their KWM-2 or S/Line separates for a long time should consider a DIY rebuild. But as I described in one of the quoted CCA links above, the rebuild goes a whole lot easier when there's an extra 70K-2 PTO to temporarily disassemble and use as a reference. 

If you still don't want to attempt it, then I agree it's worth contacting Pete, K2LRC:

http://www.k2lrc.com

Paul, W9AC
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W3SLK

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Re: Any 70K-2 Collins PTO rebuilders out there?
« Reply #5 on: November 05, 2021, 06:27:55 AM »

Ray Osterwald did a 2-part article in Electric Radio about the Collins PTO's and I now see that Electric Radio has them on DVD with a step-by-step procedure. Probably a compilation of everything that has been suggested here and then some.
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N6AF

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Re: Any 70K-2 Collins PTO rebuilders out there?
« Reply #6 on: December 25, 2021, 05:44:38 AM »

A follow up on my KWM-2 PTO repair. I pulled the guts out of the can again and this time armed with freeze-spray I isolated C303 3000 pF as the temperature sensitive part and replaced it. Frequency jumping cured and dial tracking is superb!  Along the way the weak 6AU6 was also replaced and I added Zener regulation to its plate/screen supply line. Running like a champ!  The $250 KWM-2 (including PS) is now a fully working bargain. Thanks for the suggested references.
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