[Elecraft] AGC adjustment

[k6se@juno.com]

I just replaced R1 on my K2's control board with a 22k resistor.  The
original 8-volt regulator is still in place, outputting 8.35 VDC.  With
no antenna connected, no signal and RF gain fully CW, I measured the
following:

U2-5 = 3.74 volts

U2-1 (AGC on) = 3.73 volts

U2-1 (AGC off) = 3.23 volts

Previously, with the original 51k in parallel with a 100k (~33k), I
measured the following:

U2-5 = 3.87 volts

U2-1 (AGC on) = 3.80 volts

U2-1 (AGC off) = 3.44 volts

Notice that the AGC output at U2-1 when switching the AGC on/off
previously (with R1 ~ 33k) had a delta of 0.36 volts.  After replacing R1
with 22k, the delta is 0.50 volts.

The greater delta apparently is why the AGC on/off background noise
difference is greater as I decrease the value of R1.  As the value of R1
decreases, the AGC OFF output at U2-1 decreases faster than the AGC ON
output at U2-1.

The S-meter gets hotter each time I reduce the value of R1, as it should.

My goal is to have the U2-1 difference between AGC ON and AGC OFF be only
slight, so as to have the receiver operating at maximum gain with the AGC
ON and no signal received.  Each time I reduce the value of R1, the gain
of the receiver increases, but it increases faster with the AGC OFF than
with the AGC ON.

How now, brown cow?

73, de Earl, K6SE