[Elecraft] K2 10W PA problem

[Don Wilhelm]

Guido,

Did you also change Q11 and Q13?  What I suspect is that the bias is 
incorrect, and increases during keydown causing the current draw by Q7 
and Q8 to increase.

Often Q11 and Q13 are damaged by a PA transistor failure, and if they 
are not changed, they will in turn damage the replacement Q7 and Q8.

Where did you obtain the 2SC1969 transistors?  I have heard reports of 
Chinese transistors that do not meet specification and fail quickly.
Currently, the only source of 2SC1969 transistors that I trust is those 
at Elecraft - order K2PAKIT, it includes the PA transistors, 
replacements for Q11 and Q13 as well as R50 if needed, along with 
mounting hardware for the PA transistors.

73,
Don W3FPR

Guido Tedeschi wrote:
> A friend asked to me to repair his K2 10W which has a strange problem:
> too high current in TX (1.2A even with 0.5W) and current that
> increases during key-down until HiCurr protection.
> Already changed the 2 x 2SC1969 PA transistors and re-winded the
> output transformer, but nothing changed: the voltages on PA and driver
> seem OK, the power from driver and the power output remain stable
> during key-down, but the current increases...
> What could be the issue?
> Before spending more time on troubleshooting, has someone had and
> solved the same problem?
> Thanks and 73
> Guido, ik2bcp
>
>