[ARC5] ARC-2: IF Regeneration is a "No"

[David Stinson]

More on the RT-91/ARC-2 IF experiments:

I have experimented with regeneration in the IF stages.
Narrowing IF bandwidth by putting the stages into
regeneration is an old trick that has worked well
for many sets. There is even an old article about 
doing that in the ARC-2 with involved some 
destructive mods and is, therefore, a "non-starter."
This mod may have worked for an ARC-2 that
was going to sit on 3880 KC forever, but my 
experiments with regeneration show that it 
will *not* work if you want to preserve the 
original functionality of the set.
The Collins engineers built a marvel. When properly 
aligned, the tunable IF tracks the RF stages very well.
There are two adjustments for each RF and IF tuned-
circuit: a "main" and a "trimmer." The manual states 
that the trimmer adjustment is very broad and may 
not exhibit a "peak." That's putting it mildly; I can't 
find a peak with a scope. They give a tedious, 
hair-pulling suggestion of going back-and-forth
with the "main" tuning, which must be carefully reset to 
its original position each time. But I find no significant
difference in stage gain from one end of the tuning 
range to another despite the "trimmer" setting.
IMHO, the possibility of introducing "human errors"
while diddling these trimmers is not worth the dB
or so you'll get from fooling with them.
And they have a recessed adjustment that is maddening.
If one introduces any level of regeneration into the IF,
the shape of the IF bandpass changes radically and 
varies with the tuning setting. My first attempt 
at introducing a modest level of feedback did indeed 
sharpened the bandpass... and moved the peak 9 KCs!
Retuning the IF got the peak closer, but now the IF
tuning would not track the RF tuning correctly even 
across the width of the 80 Meter band.
As I stated before- the author of the old article may
have had success with this if his ARC-2 never left
3870-3890 KC, but even that required a "hack" to 
the front panel to add a Regen Level pot.
IF Regeneration is not an option.
I have not yet tried the author's other suggestion of
changing the 5 pFd coupling caps to 3 pFd.
Do you think such a small change will bring a 
worthwhile benefit?
More as results come it.
73 DE Dave AB5S