[Elecraft] K3 AF/RF Mod

[N2TK]

Paul,
I like  what you did. I agree. I don't use the RF gain controls much if at
all. I use the AF gain controls for the main and sub receiver the most. If I
remember correctly the prototype K3 had the controls the way you changed
them.
Will have to give some thought to making the mod.

73,
N2TK, Tony

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Paul Christensen
Sent: Thursday, September 10, 2009 12:28 PM
To: elecraft at mailman.qth.net
Subject: [Elecraft] K3 AF/RF Mod

Okay, I couldn't leave well enough alone...

Yesterday morning, I was working a T30 station split on 40m with the K3's 
Sub Rx and became a bit unnerved with the manipulation of the K3's "Sub AF" 
control when balancing between Main and Sub receivers.  Multiple quick 
reaches for the "balance" function on the upper Sub AF control's outer ring 
was causing me to accidentally come in contact with the other controls. 
Looking at the K3 schematic, all four controls (Main AF, Sub AF, Main RF, 
and Sub RF) are all 10K in value.  Even when the K3's AF control furnction 
menu is selected for "Normal," rather than AF "Balance," a similar issue can

arrise when trying to quickly balance the Main/Sub AF controls on one shaft.

I removed the front panel to inspect the Front Panel PCB and thought a swap 
of the Sub AF and Main RF controls could be easily accomplished.  Here's a 
"before" photo of the PCB area:

http://216.229.20.37/images/K3-AF-1.jpg

And the "after" wiring...

http://216.229.20.37/images/K3-AF-2.jpg

A hot glue gun can be used near the 5-pin header to keep the two ribbon 
cables from interfering with future front panel extractions and insertions. 
Now, the upper controls handles Main AF (inner) + Main RF/SQL (outer).  The 
lower controls handle Sub AF/Balance (inner) and Sub RF (outer).

When I engage split operations and use the Sub Rx, manipulating the balance 
between Main AF and Sub RF is easier with a bit less propensity to 
accidentally come in contact with the adjacent controls since: (1) the 
Main/Sub AF balance function is now on the inner concentric control and 
extends out further from the front panel than the outer concentric ring; and

(2) the balance function is now moved to the bottom where the hand can 
approach the control from the bottom rather than directly in-line with the 
knob.

If needed later for a sale, reversal of the mod is very easy.  Certainly, 
this mod is not for everyone.  However, I would think that in later PCB 
revisions, Elecraft could provide the option of selecting the existing 
format or the modified format at the time of purchase -- or to the builder 
who simply makes a few header pin changes during construction.

Of course, the front panel legends also need changing and that's probably 
the biggest drawback to the mod.  In my case, I will use new legends printed

from a Brother 'P-Touch' printer -- printed with white lettering against 
black background tape.   Font size and type is adjustable to match the 
existing legends on the K3.

Paul, W9AC
 

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