Oliver,
High Current coupled with low power output is normally an indication of
a problem with the Low Pass Filter or with T4. The first thing to check
is the Low Pass Filter. Check the capacitor values for the 20/30 meter
(and 80 meter) low pass and count (and recount) the turns on the
toroids. Be certain to count only the turns that pass through the
center of the core.
Check to be certain T4 is wound correctly - 2 turns of green wire and 3
turns of white wire.
As a last resort, there may be a problem with one of the PA output
transistors (Q7 and Q8). One could be weak and hogging current in an
attempt to produce the requested power output - they have sufficient
gain on some bands to produce adequate power even if one is weak. The
easiest way to determine that is to replace them both.
73,
Don W3FPR
Oliver Johns wrote:
Dear folks,
I'm wondering if this is a bug, or perhaps a known feature of the K2.
Comments appreciated.
The following observations are made with the Max current set to 3.5
A. The K2 is running into a DL1 dummy load, directly connected by a
male-male BNC adapter. The KAT2 is not installed. The power supply
is rated at 4 A continuous, 6 A intermittent. There is very little
drop in the nominal 13.6 voltage when the Xmtr is keyed. The BP
filters have been aligned carefully as per the manual page 80.
On 40, 20, 17, 15, 12, 10 meters, I can set the Power knob on the K2
to its maximum of 15.2 Watts with no sign of Hi Cur. The actual
current drains run somewhere around 2.5 A. The actual power out
varies, of course, but there is no problem with Hi Cur. The powers
read from the display are: 40 = 14.9 20 = 14.5 17 = 14.6 15 =
14.1 12 = 10.9 10 = 10.0. Notice that the power decreases on 12
and 10, as evidently would be expected since the final is less
efficient on these high bands.
But on 80 meters, there will be Hi Cur for any power knob setting
above 8 Watts. At 8 Watts, the power read from the display is 8.1
Watts and the current drain is about 2.25 A. But much above that and
the current goes to the maximum and is then limited back.
And on 30 meters there will be Hi Cur for any power knob setting above
10 Watts. At 10 Watts, the power read from the display is 9.8 Watts
and the current drain is 3.4 A.
The 30 meter case is particularly puzzling to me. The BP inductors
for 30 meters are shared with 20 meters, and the LP filter for the two
bands is the same. So any soldering error there would probably also
show up on 20 meters. And 30 meters is lower in frequency than 20
meters and so should be more not less efficient.
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