[Elecraft] Query re: Builder alert #19

[John, KI6WX]

Dave;
When C44 is placed across R7, it can cause U3A and Q11 to oscillate under
some conditions.  While the readout of the current is very stable, the
oscillations can cause the current readout to underestimate the true current
by 25% or more, especially on the lower frequency bands.  The only way to
tell if you have this problem is to probe with a scope at the collector of
Q11.  You can also place an amp meter in series with the K2 and compare its
readings with the internal K2 readings while transmitting on the lower
frequency bands.
-John
 KI6WX


> My K2 serial 1892, has always shown erratic current measurement when
running
> from my main shack power supply. While not annoying enough to mention on
the
> reflector, I was pleased to see Builder Alert #17 fixed it by the addition
> of a 0.1 uF capacitor (C44) across R7 on the control board. Just
increasing
> C42 to 0.1 uF doesn't fix the erratic reading for me, adding C44 was a
> complete fix.
>
> I noticed today that Builder alert #19 recommends not fitting C44... any
> thoughts on which way to go... do I suffer with an erratic current
> measurement or leave C44 in place??
>
> Happy new year to all fellow Elecrafters.
>
> Dave, G4AON
>