[R-390] Cosmos Drift

[Jim M.]

Capacitors changing value with temperature?  Believe it or not I have seen 
the .005 bypass caps in a Collins PTO go bad with age, change values with 
temperature.  A change in screen or other bypass caps could cause a slight 
change in frequency.  Otherwise, a temperature compensated mica cap inside 
the can could be failing.  Maybe mechanical drift?  If the oldham coupler is 
too tight against the PTO side, mechanical variations could cause drift. 
There should be about 1/32 inch gap both sides of the oldham coupler. 
Maybe these could be causes other than the tube...


----- Original Message ----- 
From: "Scott Bauer" <odyslim at comcast.net>
To: "Cecil Acuff" <chacuff at cableone.net>
Cc: "R-390 at Mailman. Qth. Net" <r-390 at mailman.qth.net>
Sent: Wednesday, August 30, 2006 10:09 PM
Subject: Re: [R-390] Cosmos Drift


>  I bought 120 5749's all from the Philips contract dated 1987. These tube 
> have been
> giving me a lot of trouble in the PTO as well as V505 (a) V508 non a. The 
> tube will
> work fine for the first 40-60 hours and then start acting up. Any body 
> want to but some
> NOS tubes? :-)
>
> Cecil Acuff wrote:
>> Still got a 3TF7 in it....or another solution such Kielbasa.
>>
>> Could be power line fluctuations, room temp changes.  You are not running 
>> the ovens are you....shouldn't be...
>>
>> Might be the tube but I've heard of more problems with new tubes in PTO's 
>> than well seasoned ones...
>>
>> Cecil...
>> ----- Original Message ----- From: "Jon" <jonklinkhamer at comcast.net>
>> To: "R-390 at Mailman. Qth. Net" <r-390 at mailman.qth.net>
>> Sent: Wednesday, August 30, 2006 4:03 PM
>> Subject: [R-390] Cosmos Drift
>>
>>
>>> Hello to the group, hope everyone is having a great summer.
>>>
>>> If I had to write about my summer vacation at 44, I would tell the class 
>>> how
>>> I performed major surgery on a Cosmos PTO. How every night I turned 40
>>> screws,that are the size of an ant with a homebrewed tool, which 
>>> sometimes
>>> caused havoc in restricting the turning of the shaft to messing up the 
>>> end
>>> points, to interaction between other cal points, how I must of taken 
>>> apart
>>> that $#%#$ thing 14 billon times. It is truly amazing that it is still
>>> working. Sorry, I had to get that out of my system. Now I was curious on
>>> what I will call long term drift. After installation of the PTO into the
>>> radio with it connected to a freq counter, I let it warm up for 48 hours
>>> before I cal'd it. After which, I brought it back to the set point in 
>>> this
>>> case, 3.455000Mhz and let it sit. It is now over 3 days and the PTO has
>>> drifted over 1000Hz increasing in frequency. It seems to me that it will 
>>> not
>>> settle out like I thought it would. I was wondering if anyone else has
>>> experienced this or knows any 'quick' remedies. I would appreciate any
>>> comments at all. Thanks for the bandwidth!
>>>
>>> 73,Jon
>>>
>>>
>>>
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>>
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