"Jimmie D" wrote in message
...
I am trying to build a small class C RF amp for 160 AM. The amp is to be
plated modulated and I have about 12 watts of audio available. I have built
amps before(30 years ago) but I have never built one around a modulator,
previously I built the modulator to suit the amp. Any help with tube and
voltage selections would be greatly appreciated.

Jimmie

I presume you mean 160 KHz, not MHz.

Almost any of the N channel power FETs intended for switching power supply
use will work at 160 KHz.. Forget about the 12W amp; you would need a low
impedance modulation transformer for that. I would start with a non
regulated power supply at about 30 volts, and run that to a buck regulator.
Set the quiescent voltage to 12 V. Now, AC couple the audio ( a few
milliwatts) into the regulator reference input, and adjust the audio
amplitude so that the regulator output swings between 0 and 24V. That is the
supply for the power FET.

To operate in class C, you will want to drive the gate with a rectangular
waveform. I would start with about 25% duty cycle. There will be a tuned
circuit at the output of the FET; that has to have a fairly low loaded Q,
or you will cut off the sidebands.

Actually, It should be possible to do this without even having a separate RF
amplifier. Run the buck regulator at 160 KHz with almost no filtering at the
output. The regulator output will be AM modulated 160 KHz. Filter it in an
LPF.

If you meant 160 MHz, the first paragraph still applies. Use the regulator
output to power an RF transistor operating at 160 MHz.

Tam