[Elecraft] K2 10W PA problem

[Guido Tedeschi]

I removed the PA transistors and measured the bias, which is 0.64V and 
this should be fine...
Probably, it was only an heatsinking problem, unless the TX current is 
wrong: without the PA transistors, with RF Power set to 5.0W (with any 
value greater than 0.1W is the same), the TUNE current is 0.62A (0.24A 
in RX)
Is it ok 0.62A?
Thanks and 73
Guido, ik2bcp

Don Wilhelm wrote:
> Guido,
>
> Since the normal base to emitter voltage on the PA transistors self 
> limits at about 0.63 volts, the best way to check the bias voltage is 
> to remove the PA transistors and measure it.  With the PA transistors 
> out, if the base voltage during a TUNE is between  0.6 and 0.63 volts, 
> then Q11 and Q13 are doing their job and you have faulty PA transistors.
>
> For proper heatsinking, yes the PA transistors must fit flat against 
> the heatsink.  Before soldering the PA transistors in place, I 
> position them on their mounting hardware and secure them temporarily 
> with a nut (no lockwasher, no thermal pad).  That places the tab 
> parallel with the RF board.
> Solder the transistors and remove the nuts - add the thermal pads and 
> mount the heatsink.
>
> 73,
> Don W3FPR