[Elecraft] voltmeter offset and accuracy in K2

[Steve Jackson]

NB:  this posting is about an Elecraft radio

;-)

* * *

I was thinking about doing two things to my vereable
K2 #0771, as I wait for new Elecraft toys:  

... one is to re-jigger the divider resistors to
offset the K2 voltmeter so it reads what my actual
input-port voltage is, rather than the "internal"
voltage

and

...two was changing the TO-220 regulator(s) to some
kind of precision type ... could not remember if it
was the 8V LVDO or the plain-old 7805 type that set
the reference voltage for other measurements.  Wasn't
obvious from the schematic, at first.

On the matter of the offset, I suppose that the
voltmeter's ultimate accuracy will be reduced a bit
because a fixed offset won't compensate for the
actual, varying drop through the polarity-protect
diode, as that will vary over the IsubF ... however,
I've switched mine to the newer Schottky type -- and
aren't they V-drop-flatter over the current curve than
the original?

And on the second matter of the regulator precision,
maybe I am mistaken about the availability of
more-accurate TO-220 parts.  What is the typical load
that the 8V rail has?  I'm guessing a 1 amp regulator
will suffice.

Which regulator was the "critical" voltage unit?  It
was the +5v, right?  

Steve KZ1X/4




		
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