[Elecraft] K2 PA replacements

[Don Wilhelm]

Don,

The safe thing to do is replace Q11 and Q13 in addition to Q7 and Q8.  
Sometimes Q11 and Q13 fail as a secondary failure when the PA 
transistors fail.

On the part where you say there is only 7 watts out while the K2 shows 
15 watts, I am going to make a lot of "IF" statements - read carefully 
for the conditions.
IF you have only the base K2 (no KAT2, no KPA100) - you must have a 50 
ohm non-reactive load to have valid power readings on the K2 display.  
Connect a good 50 ohm load and you wattmeter to check.  If the K2 power 
display does not track, check the soldering around the resistors 
associated with D9 - occasionally, D9 may fail, but that is not a 
frequent occurrence.

OTOH, if you have the KAT2, KPA100 or KAT100 installed, those each have 
wattmeters - the wattmeters need to be balanced and calibrated (see the 
manual for the particular option).  Check the 2 diodes (2N5711s) 
associated with the wattmeter and replace if they are questionable 
before attempting to balance and calibrate the wattmeter.  If you cannot 
achieve a good null when balancing the wattmeter AND the wattmeter has 
worked correctly before, damaged diodes are the most likely cause.  If 
it has never worked right, there is a problem with the bifilar wound 
transformer or soldering.

I would give you more specific information, but I am on vacation this 
week and do not have all the manuals with me.

73,
Don W3FPR

On 12/15/2011 12:41 PM, NK6A-Don Minkoff wrote:
> The K2PAKIT comes complete with additional replacement bias transistors,
> Q11 and Q13.  Although the K2 does operate up to 7W out (while showing
> 15W) , there is no adjustment in a linear fashion with the power knob.
> 2W out when showing 5W on the display. Should I replace automatically
> the bias transistors along with Q7 and Q8? That was my plan.  Just
> wanted to check with any experts out there.
> Thanks,
>
> Don, NK6A
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>