[Elecraft] Replacement board for K3 KANT3 Progress Report

[David Olean]

I have several K3 radios, and none of them have the antenna tuner. For a 
long time, I never needed one. I really could use a switchable antenna 
option however.  I saw a comment on this reflector a few years ago, 
about a fellow who made up a replacement board to provide that function. 
He offered the empty boards along with a parts list. I bought one and 
then promptly forgot about it. The board is dated 2016.  Mine is labeled 
"Copyright Arcom 2016 KANT3 REV 1.0."  When I found it in my junk pile, 
I had no idea what it was! A few folks on this reflector clued me in and 
I decided to try to build it up. The construction is quite simple with 
the exception of three teeny weeny surface mount shift registers: 
TPIC6C596PW in the SO16 size.

I am 76 years old and started to have hand tremors about 15 or 20 years 
ago. It has progressively gotten worse to the point where I was a bit 
worried that I would botch the solder job with these small parts. I can 
still solder hand wired and leaded components, but chip caps and FETs in 
small sizes can be impossible. My 432 MHz preamp has a HEMT that looks 
like a grain of sand. When it gave up the ghost, I had to farm that job 
out!  Well I decided to try and slide the KANT3  IC parts into position. 
Then I perched a small 1/4" socket on top to hold it down. I figured if 
I could solder one lead down I might be in good shape. Well it worked. I 
managed to solder all three shift registers to the board.

I installed the new board in one of my K3s and set it up as a KAT3. It 
now will switch between Antenna1 and Antenna2 just fine. I did not read 
the instructions carefully. I should have!  The 12 volt Omron relays do 
not go on the board with the groundplane (and where they are silk 
screened!)  You must put them on the backside of the board. There was 
also a comment about shorting out pins 13 & 14 of one of the shift 
registers. Looking at the schematic, I think this is to give added 
current capability for driving the two relay coils.  I also found an 
unlisted part, C-14, a 0.01 capacitor that goes across one of the relay 
coils. Make a note of that if you are ordering parts.    Also be aware 
that the shift register is available in various package sizes. Be sure 
you get the correct one. I had to re order mine!

I know a few folks had ordered the PC boards, and at least one made the 
same mistake with the shift register package that I did. So it all works 
just fine, and is a great addition for my K3. I can now easily switch 
between my 160 meter vertical and my outboard antenna tuner and doublet 
for 80M and above.

73

Dave K1WHS