[R-390] replacement R390A gear clamp source

[Bob kb8tq]

Hi

20 years after Motorola made their last R-390, the girls from that production line still had some
really nasty stuff to say about setting up PTO’s. 

The PTO’s have been an issue since the very beginning. 

Bob

> On Jul 25, 2026, at 3:01 PM, Jim Whartenby via R-390 <r-390 at mailman.qth.net> wrote:
> 
> Interesting document, worth reading before tearing into the R-390A
> https://vk6ada.com.au/collins-r-390a-urr-ten-most-common-failures-ranked-by-community-report-frequency/
> Jim
> Logic is a systematic method of coming to the wrong conclusion with confidence.  Murphy 
> 
>    On Saturday, July 25, 2026 at 01:29:09 PM CDT, SCOTT Barry via R-390 <r-390 at mailman.qth.net> wrote:   
> 
> Rats.  All this talk made me get my counter out and, today, my Collins 
> PTO is running about 1.529 kc too wide (1.001529 mc end-to-end).  I will 
> probably have to see if I can get that closer.
> 
> 73,
> Barry - N4BUQ
>> Paul....
>> 
>> Seeing that you have a Cosmos PTO, there are 2 seperate adjustments. 
>> One sets the end to end 1Mc ten turn coverage, and another that sets 
>> the 25kc points which is much more involved and difficult to adjust.
>> 
>> You should do some reading about the Cosmos adjustments...
>> 
>> 73...Jordan VE6ZT
>> 
>> ----- Original Message ----- From: "Paul Roche" <rochep at comcast.net>
>> To: "Jordan Arndt" <Outposter30 at shaw.ca>
>> Cc: "Barry" <n4buq at knology.net>; "R-390 Mailing List" 
>> <r-390 at mailman.qth.net>
>> Sent: Saturday, July 25, 2026 9:45 AM
>> Subject: Re: [R-390] replacement R390A gear clamp source
>> 
>> 
>> It is a Cosmos 136-1 PTO, SN 21195 (I think that’s means it’s a pretty 
>> late one).
>> Sent from my iPhone
>> 
>>> On Jul 25, 2026, at 11:23 AM, Jordan Arndt <Outposter30 at shaw.ca> wrote:
>>> 
>>> Paul....What you're seeeing is the cover for the adjustment....the 
>>> real adjustemnt is hidden behind that cover screw which you need to 
>>> remove. Behind it is a small slotted brass rod that you adjust...I 
>>> wouldn't try to adjust it until you're sure you have everything 
>>> properly synchronized.
>>> 
>>> What type of PTO is it...? Collins type or Cosmos type...?
>>> 
>>> YMMV....73...Jordan VE6ZT
>> 
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