I've been testing the KPA100 that I've just finished building and have
found a problem.
The symptoms are a little weird, so bear with me.
On 40m and 80m SSB, once the K2 PWR control is set to 11W or over, the
RF output corresponds to peak full power. This seems to be frequency
dependent
and the audio frequency at which peak power is delivered changes between
USB and
LSB. When I whistle into the mike, I see full output on a scope and the
power
indication on the K2 also shows full scale, and the K2/KPA is drawing
around 20A.
If I turn the power to 10W, I see the expected power level on these two
bands.
If I turn the PA menu option to OFF, then power delivery throughout the
power range
0.1 to 15W is as expected.
On these two bands, CW power control is fine with the PA turned on, and
varies
as expected from 0-10, and then with tha PA on from 11W to 100W+.
On 160m, 30m, 20m, SSB (USB and LSB) power delivery is correct.
I didn't try any bands higher than 20m for this.
So the problem seems to be PA ON only, affecting SSB only (USB and LSB)
and only on two bands. The base K2 seems fine on these two bands within its
normal 15W range. It appears as if there is a PA ALC/power control problem
on these two bands in SSB mode.
All the resistance checks and voltage checks during construction were fine.
The only ones that were slightly off were the PA transistor base
resistance check.
I measured 11.6 ohms instead of the 12-18 ohms indicated on my DMM.
All the others were within spec.I figured that 11.6 was within 5% of 12 and
that might be DMM inaccuracy.
Any ideas where to start looking for the problem?
Thanks,
David, M0DHO.
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