[Collins] 51J4 Crystal Filter

[Dr. Gerald N. Johnson]

Often micas built in an IF transformer have no package and no label.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association

On 9/24/2011 9:57 AM, Al Parker wrote:
> Hi John,
> 	If you can see the capacitor(s), read the value of it.  Go to:
> <http://www.wiktel.com/standards/capa.htm>  for info on how.  75pf might
> be right, or close, but it's easy to ck.   (my skem doesn't show valurs
> there either.)
> 	Does the alignment peak when you adjust either?  If so, they're
> probably OK.  But, micas, especially those small one, are being found
> leaky more and more now.  I'm presently working on a Collins R-390/URR
> that has had 4 bad ones in it (so far), and one resistor that was fully
> open, no signs of everheating or physical damage.  One of the caps
> showed about 25k resistance even at the 9vdc that the Fluke puts on it,
> the others were OK on the Fluke, but when ckd on the bench megger, they
> started showing resistance at 50vdc or so.
> 	This xtal phasing stage has no gain, actually has some loss, so don't
> expect signals to get stronger thru it.
> 	hope this helps some,
> 73,
> 	
> Al, W8UT
> www.boatanchors.org
> www.hammarlund.info
>
> "There is nothing -- absolutely nothing -- half so much
> worth doing as simply messing about in boats"
> Ratty, to Mole
>
> On 9/24/2011 9:18 AM, Jon L. Turner wrote:
>> Hello All,
>>
>> I am going through T101 and T102 on a 51J4 that I purchased. I am wondering if anyone knows the value of the capacitors inside the cans. My tester shows 75 pf on the one in T101. I am not seeing a value on them in the schematic. The receiver seems to be low on sensitivity and it is looking like it is in this area of the receiver.
>>
>> Thank you,
>>
>> JT
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