[Elecraft] KPA100 Problem

[Harvey Howell]

 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" <w3fpr at earthlink.net>
To: "Harvey Howell" <h.r.howell at worldnet.att.net>; 
<elecraft at 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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