[Collins] 51J4 Alignment Question

[Dr. Gerald N. Johnson]

I think the product detector mod in my J3 is based on the one by Cap. 
Paul Lee in CQ magazine April 1961. The AVC mod was later and is space 
wired, involves at least one high value resistor.

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

On 8/22/2013 9:40 AM, Al Parker wrote:
> Hi Carl, et al,
> I have done the same things to several R-388/51-J's, with very
> acceptable results.
> 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 8/22/2013 9:39 AM, Carl wrote:
>> Thanks, I was wondering about those mods and any results from others.
>> It will give me a reference point.
>>
>> Carl
>> KM1H
>>
>>
>>
>> ----- Original Message ----- From: "Grant Youngman" <nq5t at tx.rr.com>
>> To: "Carl" <km1h at jeremy.mv.com>
>> Cc: "Collins at listserve.com" <collins at listserve.com>;
>> <collins at mailman.qth.net>
>> Sent: Wednesday, August 21, 2013 9:43 PM
>> Subject: Re: [Collins] 51J4 Alignment Question
>>
>>
>>
>>> And what were those changes Grant? Mine is still a virgin.
>>>
>>
>> The SSB/AGC changes I installed are in HSN issues #26, 28, and 36.
>>
>> 1. I had to increase the coupling cap for IF input to the 6BE6 product
>> detector to 4 pf (from 2 pf) to equalize AM and SSB audio levels. I did
>> not install a variable cap as Lankford suggested, but experimented with
>> fixed values. (HSN #28, 36). I also haven't installed the switchable
>> AGC speed option from HSN #36 since I don't have the switch to fit in
>> the tight space.
>>
>> 2. Lankford determined a value of 22K ohms in series with the diode
>> between V110B pin 3 and V11A pin 2 (HSN #26) as a compromise between
>> minimizing AGC overshoot and attack time. I found the resulting attack
>> time (about 3 ms) slow enough to cause a slight "pop" on the attack for
>> relatively strong signals. I reduced the value of this resistor to
>> 2.2K. There is no (audible) overshoot, and no detector overload on the
>> leading edge of strong signals. The result is very smooth sounding AGC
>> action and clean SSB recovery. The revised AGC plays well on AM, too.
>> I was tempted to put a variable resistor in that spot for further
>> experimentation, but life is short and it works well enough.
>>
>> YMMV
>>
>> Grant NQ5T
>>
>>
>>
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