There also seems to be some real-world question. I've been operating
the WW Digi contest this morning, and find that running at 500 watts out
vs 1500 watts out,with similar sequences of transmissions there is about
a 10-degree difference in temperature as reported by the amp.
73, Pete N4ZR
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On 8/31/2019 10:15 AM, Roger D Johnson wrote:
I think I've discovered a fly in my ointment! The efficiency
that the amp displays is based on it's determination of the
output power. If the amp is looking into a higher Z load,
the indicated power is greater than normal resulting in a
higher efficiency reading.
Oh well, back to the drawing board!
73, Roger
On 8/31/2019 9:32 AM, Roger D Johnson wrote:
It occurred to me that the KPA1500's built in tuner might be of
some help.
Here's my reasoning. If we decrease the drive power to lessen
the output power but keep the same voltage, the amplifier wants
to see a higher load impedance.
Here are the results of some quick tests:
Base line is the amp set for 1000 watts output and eff is 44%
I the set the tuner so the amp "sees" a load of 60 Ohms (actually)
58 Ohms with the values of L and C available. Eff went up to 53%!
I then set the tuner to present a 70 Ohm load (actually 68 Ohms).
Eff went up to 59%!
This was into a dummy load. I realize that, if you're using the tuner
to match an antenna, this could be very complicated.
If Elecraft could figure some way to give us a choice of voltages
for differing power levels, this problem would go away.
73, Roger
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