[R-390] R-390 rf gain

[Dan Merz]

Randy,  this mod is well known to be an easy "fix" to improve fast attack on
ssb signals and does improve the set (so-called "Lankford mod").  The
connections you describe are what I have in my set.    It doesn't eliminate
the need to ride the rf gain control to accommodate weak and strong ssb
signals,  which is somewhat inherent with the relatively weak  bfo
injection relative to strong signals.  I only conquered this situation by
attaching an external product detector with its own agc circuit.  There are
other fixes,  involving on-board product detectors etc. and another somewhat
more elaborate mod similar to the one you describe.  

I'm not sure what you mean  by "effective"... Does it affect the meter
response on am signals over the whole range or just for the last 1/4
rotation?  I think normal is for the meter indication to drop over the whole
range of rf control rotation for a strong am station,  such as a strong
broadcast station.  But on weaker stations,  the effect of the first part of
the rotation from lowest gain may not be apparent.   Dan. 

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Ziegenbein, Randy
Sent: Tuesday, September 06, 2005 12:57 PM
To: r-390 at mailman.qth.net
Subject: [R-390] R-390 rf gain


I'm new to the R-390A world and have a couple of questions.

My 390A is a Collins first production run and has a mod so it supposedly
receives SSB better by a couple of 4148 diodes in the agc ckt (one in
parallel with R-547, grid of the AGC time constant, one in parallel with
R546, grid and plate of the AGC rectifier ckt, and finally a 47 pf in
parallel with C535, which is the coupling cap between the BFO and the
Detector.  
Is this a good mod? 
 
Next, the RF gain control seems to only be effective the last
1/4 turn clockwise (man or agc modes).  Is this normal or do you think the
pot is bad or some other problem in the rf gain control circuit?  
Or is it a result of the AGC mods above?

73,
Randy, K6RCZ
_____________________________________________________________
R-390 mailing list
Home: http://mailman.qth.net/mailman/listinfo/r-390
Help: http://mailman.qth.net/faq.htm
Post: mailto:R-390 at mailman.qth.net
Unsubscribe: http://mailman.qth.net/mailman/options/r-390