[Collins] 51J4 Alignment Question

[Al Parker]

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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