Hi Andy,

This is very interesting, because 12 watts is what I think I have consistently been able to generate into the antenna before problems creep in.

I can easily accept that this amplifier may only be capable of 12 or 13 watts.

What I don't understand is why I think I am seeing a clean 25 watts into a pure resistive 50 ohm load. Can someone please check my math?

I'm running the output of the amplifier through a low pass filter, then a scopematch, then into a high quality 50 ohm load.

My scopematch circuit is here:

http://n1bug.com/n1debug/LF_ScopeMatch-20171224.jpg

Note that it is configured such that on the current sense output, 1V=1A and for voltage, 1V=50V.

Running into a pure 50 ohm resistive load I am seeing exactly 4 divisions peak to peak on the scope (2 divisions above center, 2 below).

500 mV/div * 4 divs = 2.0V peak-peak or 0.707V RMS.

0.707 * 50 (1V=50V on the scopematch) = 35.4V RMS.

35.4^2 / 50 ohms = 25 watts.

Where am I going wrong?

As a check on scopematch calibration I set my HP 3325B to 10V peak-peak, ran it through the scopematch into the same 50 ohm dummy load at 137.5 kHz. I set the scope to 50 mV/div and it read exactly 4 divisions peak-peak = .2V * 50 = 10V which seems to verify. Admittedly this verification is at a much lower power level.

73,
Paul N1BUG