[Collins] 51J4 Crystal Filter

[Carl]

True in that specific case only.
My concern is that someone is going to assume those Murata trimmers are a 
cure all in any radio and that he will be in for a nasty surprise.

In most cases the value of the deposited cap can be measured when the coil 
wires are removed as they often are unshorted when no DC is applied. A next 
closest standard value dipped mica or 1000V NPO disc is sufficient as the 
coil core has sufficient range and 10-20pf has little effect at such a low 
frequency. Ive made many swept measurements over the years.

There are several construction methods used but other than time required the 
repair is straightforward.

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: Sunday, September 25, 2011 2:06 AM
Subject: Re: [Collins] 51J4 Crystal Filter


> But the tuning capacitor is shorted by the coil at least in T101 in the 
> 51J-4. So it has DC to ground, but not across the coil. And signal level 
> at that point in the receiver isn't even going to be a few volts, else the 
> crystal would fracture. And all the tuning capacitor sees is signal 
> voltage.
>
> 73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.
>
> On 9/24/2011 8:55 PM, Carl wrote:
>> 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
>>>>
>>>>
>
>
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