[Collins] 51J4 Alignment Question

[Grant Youngman]

> 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