[Collins] 51J4 Crystal Filter

[Carl]

Those came into use around 1952-53 and are now very prown to SMD migration 
(Silver Mica Disease). I typically wind up tearing the cans apart and 
rebuilding several times a month. Hammarlund and consumer radios are very 
prone to this.

IF coil coupling plus the resonating capacity value play the role in 
determining the stage selectivity as well as gain. 120pf is the most common 
value in consumer grade 455 KHz IF's. Others may be much higher to increase 
Q or less to decrease.

Carl
KM1H


----- Original Message ----- 
From: "Dr. Gerald N. Johnson" <geraldj at weather.net>
To: <collins at mailman.qth.net>
Sent: Saturday, September 24, 2011 7:06 PM
Subject: Re: [Collins] 51J4 Crystal Filter


> 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
>> ______________________________________________________________
>>
> ______________________________________________________________
> Collins mailing list
> Home: http://mailman.qth.net/mailman/listinfo/collins
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Collins at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 10.0.1410 / Virus Database: 1520/3917 - Release Date: 09/24/11
>