[Elecraft] K2 Problems

[Don Wilhelm]

Brent,

With that clarification, yes, I can say that the PA transistors in the 
base K2 need to be changed.  If you ordered the PA transistors from 
other than Elecraft, I suggest that you do not use those transistors -  
Order the K2PAKIT from Elecraft and you will receive a matched pair of 
PA transistors plus 2 2N2222A transistors to replace those at Q11 and 
Q13.  Do replace the Q11 and Q13 transistors because they often fail 
either as the cause of the PA failure (the bias goes high) or they are 
damaged as a secondary effect from excessive voltage on the PA 
transistor bases.

What is happening is that the current draw is exceeding 5 amps and the 
resettable fuse trips turning power off (that is a good thing).

If you have the KPA100, do check D16 and D17 to see if they are 
damaged.  If they do not function properly, the K2 will go to maximum 
power and that places stress on the base K2 PA transistors. If you do 
not have the KPA100, but have either the KAT2 or KAT100, they also have 
wattmeter diodes that can be damaged by static.

I would suggest that you install a resistor across all of your feedlines 
to discharge static charges that can occur from nearby lightning, wind, 
rain or snow.  The common advice is to disconnect the antennas when not 
in use, but plugging in PL-259s are especially bad because the center 
conductor makes contact before the shell, and if there is a static 
charge on the feedline, there is no chance to bleed it off before it 
zaps those diodes.  The protection must be in the feedline rather than 
in the K2.  I use an antenna switch in the shack and switch the 
transmitters to dummy loads when not in use - my resistors are mounted 
inside the antenna switch, so I do not have to physically disconnect the 
antennas, just turn the switch.

A resistor of 5k to 100k will be effective.

73,
Don W3FPR

On 8/24/2012 4:10 PM, Brent Sutphin wrote:
> I ordered a half dozen of the 1N5711 diodes  and finals for the K2 today.  I
> also ordered several of the 2n7000 transistors. I felt like there was some
> confusion last night after my original post with the nature of my problem.
> After reading my post today it was easy to understand the confusion.
>
> When I turned it on, it came on for a few seconds then a high
> current warning and then off.
>
> I meant to say, I turned it on, it came on for a few seconds before a high
> current warning and then the radio powered down. If I turn the power off via
> the front panel power switch and back on it does the same thing again.  The
> K2 finals quickly get very hot as if they are drawing full current, all this
> in the RX mode not transmitting . I didn't attempt to transmit.
>