[Elecraft] K2 AGC

[k6se@juno.com]

A question for the experts on the K2:

The S-meter on my K2 (#2622) has always been very stingy.  Long ago I was
told by Gary Surrency of Elecraft that if I reduced R1 on the control
board to 33k, it would increase the S-meter sensitivity.  I left it
unchanged until today (although I did change the diode he mentioned to a
more "sensitive" one, which helped the S-meter slightly).

On 2 December 2002, Wayne, N6KR wrote:

"The vast majority of K2 revision A owners will NOT have to make any
change to
R1. To see a change is warranted, listen to background noise on a very
quiet
band, then turn off the AGC (by holding PRE/ATTN and AGC together). If
the
background noise comes up significantly in volume, R1 is probably
slightly too large."

With the original value of R1 (51k), I had a slight increase in
background noise when I turned off the AGC.  I then changed R1 to 47k and
that indeed made the S-meter a tad more sensitive (I had to recalibrate
the LO and HI settings), the the noise increase when turning off the AGC
was a bit more pronouced.

I then changed R1 to 33k to see what the effect would be.  The S-meter
was much more sensitive, and the increase in noise with the AGC off was
noticeably greater.

10 MHz WWV, which previously would be about S9 on the meter, is now S9
+40 dB.  This is with the preamp on and is about the same reading as on
my FT-1000MP.

My 8V regulator output is about 8.2 volts, BTW.

I understand that K2s after #3000 have a pot at R1 and that it should be
adjusted for an "AGC threshhold" of 3.9VDC.  I haven't measured the AGC
voltage, but my main concern is that past posts say that if the value of
R1 is decreased, there should be less change in background noise when
switching the AGC on and off.  My K2 has a larger change in noise with
the lower value of R1.

What gives???

73, de Earl