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 _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
