Elecraft

K3 External ALC Mod

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Roy Morris-6

K3 External ALC Mod

The mod revision sheet of the digital IO board shows the 69.8K soldered to pin #1, and the 100K soldered to pin #20. The remaining leads of these two resistors appear to be soldered to pin #9 along with one end of the 137K. The other end of the 137K goes to who knows where.

The cut trace does not show clearly what trace is to be cut and where the 137K terminates. It is also unclear if the 69.8K, 100K and the 137K resistors are just soldered to each other or are terminated to Pin #9.

Why is it necessary to use 1% resistors? Are these values critical to produce -4 volts of ALC?

Roy Morris W4WFB

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Don Wilhelm-4

Re: K3 External ALC Mod

Roy,

Yes, they are relatively critical. Only one minor point - they do not
"produce" - 4 volts of ALC, instead, they allow an ALC voltage of up to
-4 volts (from the amplifier) to be translated to the positive ALC
voltage required by the internal circuits in the K3.

If you skip to the photo on page 4, the location of the cut and the end
of the 137k resistor may be more apparent to you because the annotations
are not present.

73,
Don W3FPR

Roy Morris wrote:

> The mod revision sheet of the digital IO board shows the 69.8K
> soldered to pin #1, and the 100K soldered to pin #20. The remaining
> leads of these two resistors appear to be soldered to pin #9 along
> with one end of the 137K. The other end of the 137K goes to who
> knows where.
> The cut trace does not show clearly what trace is to be cut and where
> the 137K terminates. It is also unclear if the 69.8K, 100K and the
> 137K resistors are just soldered to each other or are terminated to
> Pin #9.
> Why is it necessary to use 1% resistors? Are these values critical to
> produce -4 volts of ALC?
> Roy Morris W4WFB
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