[R-390] Correction To "Chambers Audio Derived AGC Mod"

Sat, 03 Apr 2004 16:51:00 -0800

Dallas and others,  thanks for your patience - hard to tell from the reprint of
your article that I have whether it's HSN 27 or not -  it's titled " R390A
AGC/BFO Mods... By Dallas Lankford published June,  1990 if I'm reading their
reprint format correctly - I obtained it from Nat. Radio Club R66 reprints quite
awhile back,  and I think the only thing I didn't do was take out the 220k
resistor that one of the diodes bridges.  I just added two diodes  1N4148's.  In
some 390 postings,  this was referred to as Lankford HSN 23. As far as I can
tell from other comments,  the pinning of the meter is typical 390a or 390
action when switching from slow to med.  The quirk of hanging at a higher level
may be something else,  which I'll pursue.  I apologize for not mentioning the
390 i.f. chassis earlier but was really after information on what was normal for
the 390a agc carrier meter when switching the slow/med/fast.

At this point,  I'm thinking of trying another mod for agc published in Electric
Radio Nov 2001.  I corresponded about a year ago with Ron Deeter and he
suggested a variation of this that he put into both a 390a and  the 390 i.f.
/390a combination.  These mods do away with the suppressor grid connections.
For the most part,  I dislike extensive mod's because I mostly like to
appreciate the old sets for what they were.  But I can always stick my original
390a i.f. back in for that purpose or for the next guy that gets it.  Perhaps
someone else has tried the Electric Radio mod.  I'm not sure it'll be worth the
effort beyond what the two diodes accomplish.  My biggest desire is to
accommodate ssb signals with big strength differences without turning the rf
gain up and down constantly.

I did take a look today through the  archived FAQ's on the Lankford  agc mod
subject under 390 ssb mod's to refresh my memory on where I got the mod I made.
All the info that originally lead me to make the diode mods was there,  along
with comments of others at the time on this reflector.  There's a lot there on
the subject.

Thanks to all for the comments,   Dan.

Dallas Lankford wrote:

> Dan, You have two diodes (and I don't know what else you added, or what else
> you removed) in (to/from) your IF deck.  Whatever results I get with my
> unmodified IF deck won't tell you anything about your IF deck possible
> problems.  A lot of people have written about my AGC mods, and some of them
> have gotten it/them wrong.  Maybe you were unlucky and stumbled across one
> of those versions.  I would have to dig through my archives, but I believe
> there were two (possible three) "Lankford 2 diode AGC mods."  Which one are
> you using?  In these recent postings to the QTH R-390A reflector, when I
> referred to "my AGC mod" I meant my final one, the one which appeared in HSN
> #27.  If you don't have that mod, then K5OP Audio Derived AGC mod probably
> won't do anything for you.  Finally, you have only belatedly told me that
> your IF deck is not an R-390A IF deck, but a modifier R-390 (non-A) IF deck.
> It is likely that is why you are having those problems.
>
> Best regards,
>
> Dallas
>
> ----- Original Message -----
> From: "Dan Merz" <[email protected]>
> To: "Dallas Lankford" <[email protected]>; "R-390 List"
> <[email protected]>
> Sent: Saturday, April 03, 2004 11:11 AM
> Subject: Re: [R-390] Correction To "Chambers Audio Derived AGC Mod"
>
> > Dallas,  I changed the K5OP audio agc  gadget to the corrected config and
> it
> > seems to help a bit on the reduction of distortion on initial attack.  But
> that
> > aspect wasn't too bad without it with the diode mod in place.  I did the
> diode
> > mod myself and I'm pretty confident that it's installed the way it should
> be.
> > My story is a little more complicated than  I stated since I'm using a 390
> i.f.
> > chassis in my 390a radio but I've convinced myself that this is not the
> cause of
> > the quirk that I see.  I'll probably wait to see what characteristics you
> > observe with your unmodified i.f. chassis as far as carrier meter hang
> goes
> > since my 390a i.f. chassis also has the diode mod in it and I'd rather not
> undo
> > the mod at this point and stick it in to see its characteristic.  I would
> be
> > interested in the observation of anyone else on absence or presence of
> this
> > quirk of meter hang and whether or not the carrier meter is pinned in a
> set with
> > or without the diode mod when switching from slow to med on agc.   Dan.