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

[Llgpt@aol.com]

Having applied this modification many years ago, I would say, it it without a 
doubt essential to the proper operation of an R-390A, either for am 
broadcast/swl listening or ssb listening.

It (the two diode Lankford mod) eliminates the s-meter hang when switching to 
med agc from slow and improves listening in the am mode. Of course, It vastly 
improves the listening in ssb. I fully realize that many do not care to 
"modify" a R-390A, but that is their problem, not mine.

Having known K5OP, and Dallss for many years, I can say without reserve, that 
those who haven't chosen to make these modifications are living in the dark 
ages.

Les Locklear



In a message dated 4/3/2004 12:51:39 PM Central Standard Time, 
tetrode@comcast.net writes:
----- Original Message ----- 
>  I would be
> interested in the observation of anyone else on absence or presence of
this
> quirk of meter hang

Dan,
I've only seen this in a mechanically defective meter. You could disconnect
it and play around with it on the bench to find out.

>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.

The meter pinning is a normal characteristic of stock R-390x's when
switching from the SLOW to either of the other speeds.
Theoretically my guess it the AGC-diode mod would behave the same way, but
in reality the diode junctions may be breaking down to the large negative
pulse generated when the AGC speed is switched.
Might be a good idea to hook up a scope and take a look.

John


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