[Elecraft] K2/100 and QRP Mod.

[Ron D' Eau Claire]

> K2 #1185 has the modification from page 101 of the K2 Manual Rev
> B for improved transmitter efficiency at low power levels. It is
> CW only and I like the "safety margin" to the rated output.
>
> When the KPA100 takes over at 11 watt of drive from the K2 PA
> there will be a gap from about 7 to 11 watts where neither the K2
> PA nor the KPA100 will give output. ...
> 73 de Gerald, HB9iRF     K2 # 1185

If the "safety margin" you speak of is in the rated dissipation of the
finals, Gerald, you didn't improve it significantly by rewinding T4 for
lower power. All that did was to reduce the current drain slightly at 5
watts for a little better overall efficiency.

You have essentially the same "safety margin" with T4 wound normally if you
leave the power control sitting at 5 or 7 watts.

At least one op posting on this reflector has managed to coax over 20 watts
out of his K2. Clearly, the Elecraft team included a very large "safety
margin" in the power amplifier power dissipation when they designed the K2
finals for 10 watts. Indeed, most ops seem to grumble if they can't get 15
on some bands at least. I have run 10 to 15 watts for two years with no sign
of trouble from mine, and I do NOT have the KAT2 so my finals have to deal
with me twiddling with my manual ATU while tuning up. Of course, I do that
at reduced power (usually <G>). I'm still running with the original finals
and no sign of trouble.

So, while I can't answer your question about what the KPA100 will deliver
with 5 to 7 watts of drive, I can reassure you that you aren't endangering
your K2 finals by running them at 10 watts output in CW mode. And if you
want keep your 'safety margin', just don't turn the POWER control all the
way up.

One reason I may have had absolutely no trouble is that I purchased, quite
inexpensively, a spare set of finals for my K2. Having them sitting in the
drawer ready if needed is probably the biggest reason the ones in the rig
have continued to work just fine.

73,

Ron AC7AC
K2 # 1289





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