K2 Builder Alert #6: BFO Range
Fri, 16 Jul 1999

This applies to Field Test and current Production K2's (S/N 1-311).

We have found that the BFO adjustment range is inadequate on some units, even with MVAM108 varactor diodes at D37 and D38. The range problem can easily be corrected by increasing the size of C174 to anything from 270 to 390 pF.

We will immediately begin supplying a 330 pF capacitor with new K2s. But if you have already received your kit, you can use any suitable capacitor that you already have on hand (NPO disc, silver mica, or polystyrene). Most builders should have a 270 pF capacitor left over from the modification to C182. You could either install this capacitor in place of C174 or just solder it in parallel with C174 on the bottom of the board. If you don't have a suitable capacitor, let us know and we'll send you one.

Instructions for Correcting the BFO Range

1. Install a larger value at C174 as indicated above.

2. Replace the bottom cover of the K2 (this is important for maintaining accuracy of frequency counter readings during BFO alignment).

3. Re-test your BFO range using the procedure on page 56 of the manual. If the range is still less than 4 kHz, let us know. Typical range is 4.5 - 5.5 kHz.

4. Re-align all of your BFO settings using CAL FIL (do this on 40 meters). You may notice that CW Normal and LSB now sound better than before, particularly if you had poor BFO range.

Note: We'd like to thank Jerry, W0MC, for helping us find and correct this problem.