[Collins] 51J4 Alignment Question

[Carl]

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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