Posted by
ON4WIX on
May 27, 2006; 11:18am
URL: http://elecraft.85.s1.nabble.com/KPA-100-initial-test-problem-tp390264.html
Hi all
I've just finished building a KPA100 for my K2 s/n 5361. This kit is revision C-5, with R4 (High Voltage Bias Supply) 39k instead of 100k and 1k across RFC 3.
Up to p43 in the manual all seems to have gone well.
During Initial Testing (p20 to 23) I did measure some slight deviations from the resistances and voltages mentioned in the tables, in particular the following voltages (table page 23)
U1 pin 1: 4.93V instead of 5.0V
U1 pin 20: 4.93V instead of 5.0V
U1 pin 27: 5.63V instead of 5.8V
U1 pin 28: 5.52V instead of 5.7V
U4 pin 11: 4.93V instead of 4.93V
I assume that these voltages are close enough not to raise any suspicion.
Then, during Alignment and Installation, I measured 11.8 ohms at the bases of Q1 and Q2, which is just below the 12-16 ohms mentioned in the table at page 41.
At page 43 I ran into some seriously wrong voltages. The voltages at the cathode of D13 and pin 8 of U4 are not stable and fluctuating in a more or less repeating fashion.
At D13 I measure values between 150V and 188VDC whereas this should be a steady 90 to 150VDC.
Same at U4 pin 8: cycling between -28V and -32VDC, this should be a steady -5 to -25VDC.
I've been looking at the reflector archives but can't find any mention about this phenomenon. I have checked all soldering, component values, toroid tinning but can't see anything out of the ordinary.
Any hints as to where I should start looking are very much appreciated.
73 and thanks
Glenn ON4WIX
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