Don,
I checked T4 and discovered that it is a FT50-10 core instead of FT50-43. I
wound the proper core and all the adjustments worked out fine. K2 S/N 5404
is running fine with over 100 watts out on all bands. I do have one more
question. While working on the amp I noticed that the black coatings on the
thermal pads seem to scratch easily. Mine have a couple of minor scratches
that go thru the black. Does this reduce their ability to conduct heat away?
Should I replace them? Thanks.
Harvey KN6VP
----- Original Message -----
From: "Don Wilhelm" <[EMAIL PROTECTED]>
To: "Harvey Howell" <[EMAIL PROTECTED]>;
<elecraft@mailman.qth.net>
Sent: Sunday, June 11, 2006 8:50 PM
Subject: RE: [Elecraft] KPA100 Problem
Harvey,
At first glance it would seem like there is something awry with your
wattmeter section of the KPA100. Check the T4 windings again and check
carefully to be certain everything is well soldered with no solder
bridges.
Check the diodes for proper orientation, then try again to balance the
wattmeter bridge. If you do not get the trimmer capacitor correct, the
power and SWR indications will be 'funny', so be certain that you have a
good null (use the DVM on the test point). The capacitor setting is quite
'touchy' so adjust it very slowly waiting for your DVM to settle down with
each small change.
The increased voltages at D13 and U4 pin 8 are to be expected since the
change of R4 to 39k - the voltages in the KPA100 unfortunately have not
been
updated to reflect this change. They are NOT related to your wattmeter
problem.
73,
Don W3FPR
-----Original Message-----
Hello everyone. I almost made it to the finish line with my K2.
I'm encountering a problem with the KPA100 SWR Bridge Null
Adjustment (C1). I have everything hooked up correctly as far as
I can determine. I set the power knob for 5.0 W. Enter tune mode
and adjust C1 to get 1.0-1 SWR on the K2 display. The best I can
achieve is 3.6w and 3.4-1 SWR. When the display reads this value
my SX-200 power meter indicates about 18 watts out!! Also some of
the voltages read a little high:
D13 cathode should be 90 to 150v : reads 158v.
U4 (MAX 1406) pin 8 should be -5 to -25v : reads -28v
Test Equipment Used: DL-1 and MFJ dummy loads.
SX-200 power meter.
I have given the board a close visual inspection and nothing
looks bad. The red and green leads on T4 go to the correct pads.
Any ideas? Thanks very much.
Harvey KN6VP
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