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on A
ugust 28. 2010
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During the time there have been several suggestions do modify the SSB
Modul of the K2 do improve the the modulation which is named „a little
bit week and sometimes craspy by some users. Well known and often used
are the mods designed by John, KI6WX and Karl-Heinz, DF7KHK. The Mod
regarding the bandwith of the Xtal Filter suggested by John have been
overtaken for the series kits by elecraft some years ago.
The following description is a compilation of different mods. Frank, DJ3FR
had the chance to test all known SSB mods using a set of ten K2/100
which haven been built at the same time during a student course.
The described combination of mods if have been installed guarant a clean,
strong modulation on all bands. I have modified and tested a lot of K2
when servicing them as QRPproject supporter. The Berlin DXpedition Gang
is using now 3 modified K3/100 for DXPeditions e.g. to XV4D 5H1DF, A25/
DL7DF say they now get reported a „modulation like a man“ :-)
Improving the Quality of the modulation, Solving the
problem of less driver power on the upper bands
The following description belongs to:
1. Serialnumber K2 above > 3000
or if lower number installation of XFILMDKT 2nd Filter SSB Modification
Kit.
2. SSB PCB as describes in Manual Rev E July 20, 2004 or newer
(That means the new Xtals must be installed, caps CC and CM = 27pF, CG,
CH, CE, CK, CA, CP = 39pF)
If you modify an older K2, in any case check the Xtals on the RF board.
They must be signed with the same sign (4,915-S) as the Xtals on the SSB
board. If not, they must be replaced by the newer Xtals.
Elecraft number for replacement: K2KSB2XTLS 14 pieces paired Filter Xtals
coplete for main board and SSB board
Here we go, start with John´s Modifikation:
MOD 1: KSB2, More Gain for SSB
The original SSB board has a little bit low gain. If a mirophone with low
output is used, it cannot drive the K2 to full power at the high frequency
bands. Using microphones with higher levels it can happen, that the NE602
is over driven with causes AF clipping. This mod is a clean solution for both
problems.
John is using a PN2222 Emiter follower to cople the NE602 to the
low impedance side of transformer T2. This way he uses the Voltage
transformation of T2 and gives a much lower load to the NE602 output
stage. The 82 Ohm resistor together with the impedance of the Emitter
follower gives a good Imedance matching for the Xtal Filter. The resulting
gain of this mod in total gives a plus of about 10 dB..
The mor is easy to realize:
[ ]
Remove D4
[ ] Desolder wire number 2 and wire number 4 of T2 ( you find them next
to the NE602).
[ ] Now solder former number 4 wire to solderlug number 2 and former
