[R-390] K5OP AGC Mod & Umodified IF Decks

[Dan Merz]

Dallas,  I took a look at the posted agc mod you put on yahoo.  It's the same article I have as a reprint from Nat. Radio, called out as R66,  only cheaper this time since I think I paid them per page.  It took about 25 min with a 56K modem.  You did add a note about the difficulty of putting the complete mod. in an EAC chassis ,  located on the page of the schematic.  I didn't put in any of the the  time constant capacitors mentioned in this article,  just the diodes,  so I guess my mod would count as an earlier type,  as I left the grid/plate Miller effect circuit on  the slow position in place.  I recall that I did add the 47 pf bfo coupling cap.    And to my embarrasment,  I find you mentioned the
pinning of the carrier meter when switching from slow to medium for an unmodified circuit,  which goes away with removal of the Miller effect circuit.  So if I did read this completely  earlier,  I forgot it.  But it's good reading - maybe I'll remember it longer this time.  best regards,  Dan.

Dallas Lankford wrote:

> I put an unmodified IF deck in my R-390A a little while ago and measured its attack times with a scope using the K5OP AGC mod.  SLOW is awfully slow because of the Miller effect circuit it uses.  The SLOW attack time was about 200 milliseconds with or without K5OP.  Unacceptable for SSB.  The MED attack time with K5OP was unmeasurable because it was an awful looking curve, not the exponential curve (or approximately exponential) that we need to assign an attack time to.  It probably sounded bad to, but I didn't bother to listen.  The FAST setting is unsuitable for SSB.
>
> So there you have it.  The K5OP isn't a stand alone AGC for unmodified IF decks.  It is a helper which provides more electrons to give the optimal FAST attack needed for the SLOW AGC setting of my (last) AGC mod.
>
> When I have referred to my AGC mod, I meant the last one.  I don't recall exactly how many AGC mods I published.  Two or three.  (And there is another one that I haven't published yet, but it is just a minor variation of the "last" one.)  A lot of different people have written their versions of my AGC mods, some right, and some wrong.  So you won't have to find out the hard way that you have a wrong one, I have uploaded my last AGC mod to the FILES section of the other R-390 reflector.
>
> http://groups.yahoo.com/group/r-390/
>
> The access the file you have to register with Yahoo, and then you have to join the group.  After you have joined the group, you can click on FILES in the side bar, then click on the Dallas folder, and then download the file (there are two others, the SSB filter file, and the BFO vernier fine tuning file).  The AGC file is BIG, about 3 Megs.  It takes a while to download.  It also contains a simple mod to increase the BFO injection voltage.  The BFO injection mod may negatively effect the AGC voltage.  In that case you should re-neutralize the BFO.  This is discussed somewhere on Chuck R.'s web site, I think, and probably elsewhere.  I haven't checked this out myself because I never had any problems.
>
> The K5OP mod may work with one of my earlier (and simpler) "2 diode" mods.  But I probably won't look into that immediately because I have other irons in the fire.
>
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