AW: [Elecraft] KPA100 Hi Current on 30M

[Renardy, Martin]

Hallo Jonathan,

Welcome to "the low power group". I was running into the same problem a couple of
days ago. If the problem is just on 20m/30m and your are shure that you didn't 
mixed the gray and black toroid cores, than add two capacitors parallel to 
C80, C81. I have tested it with an other 4700 pF, which I soldered parallel to
C80, C81 at the bottom of the PCB. The problem has gone and I have now 115 Watts
Also on 20! The official fix is to increase C80, C81 to 5600 pF.

Greetings vom Germany

Martin



-----Ursprüngliche Nachricht-----
Von: elecraft-bounces at mailman.qth.net [mailto:elecraft-bounces at mailman.qth.net] Im Auftrag von Ken K3IU
Gesendet: Sonntag, 12. Juni 2005 20:29
An: 'Gottlieb, Jonathan'; elecraft at mailman.qth.net
Betreff: RE: [Elecraft] KPA100 Hi Current on 30M


Hi Jonathan:

You may well have joined "the group." But first...

Make sure that you can get at least 10 watts output on all bands with the KPA100 turned "Off" in the menu. Then you should recheck the power calibration procedure for the KPA100 unless you are very confident that it is correct. 

If both of those check out OK, then you are probably experiencing the same thing that several others (with you I think there are now 9) that are having pretty much the same problem. Elecraft and the designer are working on the problem and I'm sure there will be a solution soon. In the meantime, one of the things that has worked for some is to increase the capacitance at C80 and C81 between T1 and the bases of the PA transistor. Some have changed to 5600 pF, some have added another 4700 pF, and I ended up adding 2200 pF. One ham in England who had the problem replaced C80 and C81 with new 4700 pF caps from Elecraft and the problem remained. He then purchased locally and installed replacement new metal film resistors to replace R19 and R20 and new 4700 pF caps to replace C80 and C81 and the problem was completely resolved for him. It suggests that the provided resistors may have enough inductance to resonate with the 4700 pF cap and create a "trap" at around 10 MHz.

I encourage you to report the problem to Gary <support at elecraft.com> so that they are aware that there is another builder with this problem.

73,

Ken K3IU


-----Original Message-----
From: elecraft-bounces at mailman.qth.net [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Gottlieb, Jonathan
Sent: Sunday, June 12, 2005 12:12 PM
To: elecraft at mailman.qth.net
Subject: [Elecraft] KPA100 Hi Current on 30M

Almost finished with my KPA100.  Power output is 100 watts on all bands except 30M where I get hi current display over 55 watts.  Any suggestions?

Jonathan Gottlieb
WA3WDK

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