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.
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