[Elecraft] k2 spurious

[Don Wilhelm]

David and all,

I am a little late chiming in here, but all David's points are correct 
except for a caution on one.

The alternate winding ratio for T4 should never be used with the KSB2 or 
the KPA100 installed.  It is OK for power in CW kept below 5 watts.
If the PA is operated above 5 watts, it becomes more and more 
inefficient as the power is increased.

I have repaired several for buyers of a used K2 who had problems 
developing full output and observed that the current draw at 10 watts 
was quite high, sometimes causing HiCur messages.

73,
Don W3FPR

On 10/26/2020 8:43 PM, David Woolley wrote:
> 
> I'd expect the actual PA collector impedance to be a lot higher than the 
> impedance reflected through the transformer, as transistors and FETs 
> are, to a first approximation, current sources, although the negative 
> feedback would actually make the reverse termination impedance much 
> lower than that from the transformer.
> 
> A hint that is the case is the option for different winding ratio if you 
> are always going to use a lower maximum power.  Maximising the voltage 
> swing increases the efficiency.  The alternative ratio doesn't transform 
> the filter input impedance down so much.
>