I am currently building up a KPA100 amplifier (i.e., a recent vintage unit
purchased at the Orlando Hamcation Elecraft booth in February, 2007) and
have reached a problem during the alignment and installation phase of this
build. My basic K2 is a Rev. B model (i.e., S/N 4751).
The first weird thing that happened is in reference to the resistance values
shown on page 43 of the KPA100 manual. I have an old but serviceable Fluke
Model 29 multimeter that I used for these resistance measurements. I
connected the black probe of the multimeter to ground and the red probe to
each of the test points noted. In each case, the readings were negative in
polarity, but on an absolute scale, met all the resistance values shown in
the table. Reversing digital volt meter probe polarity (i.e., the red probe
was attached to ground) resulted in resistance values that agreed with the
page 43 values (yes - the probes were correct at the meter!!). I then
tested several conventional resistors that I had on the workbench as well as
during the continuity check of the K2 final transistors when I re-installed
the K2 heat sink (i.e., as instructed on page 45 of the KPA100 manual) and
all tests with this volt meter were normal. So, do I have a problem with
these readings or are they normal?
On page 46 of the KPA 100 manual with the amplifier connected to the K2 as
instructed, the J3 + lead (red) voltage value was -0.029 V instead of 0 V.
I. checked this measurement several times and this small but significant
voltage was consistently there. So the question is, is a small negative
voltage significant or should it be considered within a rounding value to be
0V as stated in the manual?
On page 47 of the KPA 100 manual with the amplifier connected to the K2 as
instructed, I hear the 4 MHz crystal oscillator signal very clearly.
Depending on the receiver mode (i.e. upper sideband, lower sideband, RATTY,
or CW, the signal is just violating (i.e., to 3.996 MHz) or just above the
80 m band edge. Rotating capacitor C27 to move the frequency higher has no
effect. So the questions are: How much frequency swing does C27 provide?
What is causing this lack of frequency movement? Should I be worried?
On page 47 of the KPA 100 manual with the amplifier connected to the K2 as
instructed, under the SWR Bridge Null Adjustment (CI), the SWR null trimmer
works as advertised, and I can change the SWR reading; however, I get no
power out of the amplifier with the K2 output set at 5 W. Initially I was
powering the amplifier and the K2 with a freshly charged, 12 V, 7 AH power
gel cell battery, but when I saw that the transmit power from the amplifier
was nonexistent (i.e., 0.1 W), I switched to powering this set up with a 12
V automotive storage battery reading 12.53 V (note that I was saving my
Astron 20 amp switching power supply to power the KPA 100 alone since two
power supplies are required during testing). In receive mode, the K2
display read 12.1 V and 0.36 Amps and had previously passed all receiving
tests. However, in transmit mode, the K2 flashes a momentary high current
signal, and the K2 display reads 10.3 V at 3.98 Amps with no measured power
output from the SO239 connector of the amplifier. Furthermore, if the K2
remains in tune mode for longer than 30 seconds, the final transistors heat
sink gets fairly warm, and the K2 will either shut down for a few minutes
(i.e. the thermal fuse activates) or just reboot. Removing the K2 from the
amplifier results in normal operation of the K2. This problem has
completely stopped by alignment and testing of the amplifier, and I would
appreciate any assistance that you can give me relative to this problem.
Thanks in advance for your help.
73
Les Kramer WA3SGZ
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