[Collins] 51J4 Crystal Filter

[Carl]

Umm, the primary of an IF transformer has the tubes plate voltage.

We are not discussing grid drive in a transmitter.

Carl
KM1H
----- Original Message ----- 
From: "Dr. Gerald N. Johnson" <geraldj at weather.net>
To: "Carl" <km1h at jeremy.mv.com>
Cc: <collins at mailman.qth.net>
Sent: Saturday, September 24, 2011 7:04 PM
Subject: Re: [Collins] 51J4 Crystal Filter


> But they see only signal voltage, not DC. If they saw DC or PA grid drive, 
> they would not survive.
>
> 73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association
>
> On 9/24/2011 3:57 PM, Carl wrote:
>> Those caps are rated at only 50V so dont do so well in the primary
>> circuit of IF transformers.
>>
>> Carl
>> KM1H
>>
>>
>> ----- Original Message ----- From: "Dr. Gerald N. Johnson"
>> <geraldj at weather.net>
>> To: <collins at mailman.qth.net>
>> Sent: Saturday, September 24, 2011 12:47 PM
>> Subject: Re: [Collins] 51J4 Crystal Filter
>>
>>
>>> 75 to 100 pf would be expected values, though in 75S IF cans the tuning
>>> caps are as much as 500 pf. The classic reference of receiver design,
>>> Radiotron Tube Designer's Handbook suggests 100 pf is a nice value so
>>> the tuning doesn't change too much when changing tubes that contribute 3
>>> to 8 pf to the circuit capacitance and may vary a couple pf from one
>>> tube to the next (especially if different brands).
>>>
>>> Depending on the construction, IF transformer capacitors have been known
>>> to go open. And coils too, often from the corrosion of an activated
>>> solder flux on wire smaller than hair. An ohmmeter can show the coil
>>> conductivity, and there is a simple test for an open capacitor.
>>> Temporarily wire in a capacitor, ideally a 120 pf compression mica
>>> trimmer, and tune it for a peak. If it peaks other than minimum C the
>>> original tuning cap is open. Then unhook it, check the value and solder
>>> in a fixed capacitor that value. Or for $1.14 from Mouser buy several
>>> 120 pf trimmers and leave them in the circuit if they work.
>>> http://www.mouser.com/ProductDetail/Murata/TZ03R121N169B00/?qs=sGAEpiMZZMvkLkkMVBW%252bEMgRGSj6TTuq83rzMXqvshc%3d
>>>
>>> 81-TZ03R121N169B00
>>>
>>> The switch, the variable capacitor (especially the shaft wiper), and the
>>> crystal are other possible places to lose signal in that circuit.
>>>
>>> 73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association
>>>
>>>
>>> On 9/24/2011 8:18 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: 1520/3916 - Release Date: 09/24/11
>>>
>>
>>
>
>
> -----
> 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
>