[Elecraft] K2 A->B & Crystals - One builder's experience

[Bill Coleman]

I'd been sorta busy with a new job, so I didn't find out about the A->B 
change until late in December. Just after Christmas, I ordered the A->B, 
BFO/PLL mod kit, and later the 14 crystal pack.

I got the instructions early. (THANK YOU Elecraft for putting your 
manuals on the web!) I went ahead and made all the mods I could that 
didn't require parts (like the AF Pot mod). Then came the long wait for 
the parts to get here.

The mods aren't terribly hard. I don't much like cutting traces, 
desoldering is a pain, and there's certainly a lot of disassembly and 
reassembly. But this went easily.

I'd already made the 2nd XFIL mod, so I got to skip that. I didn't have 
any PLL stability problems, either. However, I did have to add capacitors 
to get enough BFO range. My kit didn't come with any caps of the right 
value to parallel C173/174, so I had to dig some out of the junk box.

With the K2 back together, there is no noticable drift after the first 5 
minutes, and even that is greatly reduced.

I used the 20 MHz WWV trick to zero-beat the 4 MHz oscillator. (I used a 
receiver with an AM detector, and listed for the beat against the WWV 
carrier. Wait for the period from 45-55 seconds in the minute, when 
there's no tone. Now my dial calibration is MUCH better. Great tip.

My K2 is #2548, so I was a bit hesitant to order the 14 crystal upgrade. 
I finally decided that it was only $16 or so, why not. 

I had used rather thick diode lead clippings for my Crystal ground wires 
-- lower inductance that way. I managed to desolder the ground leads from 
the crystal cases without disturbing their locations on the board, so I 
re-used them. Just a little careful pending after inserting the new 
crystals was necessary.

At first, it seemed the CW filter was an S-unit or more down from the SSB 
filter. However, when I finally got all the BFO settings correct, they 
were closer. 

For my CW filter I use the progression 1.0, 0.4, 0.16, OP1. The 1.0 is a 
bit narrow for casual tuning, but it is great in contests. Some of the 
signal reduction is due to the narrow filter.

As for the change, from looking at MacCRO (a poor Mac-man's Spectrogram), 
the SSB filter is a little bit wider, with slightly steeper and deeper 
skirts, and a little flatter in the passband. (Note I already had the 2nd 
XFIL mod in place) I'd buy a K2SB option that had 15-20 crystals in it, 
if it meant I could get a flatter passband and even steeper skirts. That 
and a better VOX with Anti-VOX and a sensitivity contorl....

On the CW filter, the new crystals have a teeny bit of asymmetry at the 
1.0 setting. There's a bump on one side of the passband. It disappears at 
about a 0.8 setting or narrower. The CW filter is also a little bit down 
from what I hear with the OP1 filter. 

So, the Crystal change didn't bring any big shift on my K2. I was able to 
get my BFOs adjusted so that tuning to a 40m SWBC station results in a) a 
600 Hz carrier on CW, b) proper-sounding voice on either LSB or USB. 

Overall, I'm very pleased with the changes. The K2 really rocks.

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@arrl.net
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901