Dear Don,
Thank you very much for the tip. I found the problem. I had 2 turns
on the secondary (white) of T4 instead of 3. Fixing that solved both
the 80 meter and 30 meter problems. I guess it doesn't like
impedance mismatch. If I set the power knob at 14 watts, I now get
at least 12 watts out (on the W2 readout; not the same as actual
output of course) on all bands, all with currents under 2.8 A. So,
this case is closed. On to the next one.
You perform a real service for Elecraft assemblers. I've noted your
posts helping other people. We all owe you a very great debt of
gratitude for your patience (telling frustrated people to check and
check again, etc.) and your dedication. Again, thank you.
73,
Oliver Johns
W6ODJ
On 26 Jan 2008, at 6:13 PM, Don Wilhelm wrote:
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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