wrote:
Scott Dorsey wrote:

How high speed do you want and why don't you want to use a gas tube?
With a vacuum tube, you pretty much have to run class C in order to get
complete cutoff.

I actually want to implement class E amplification with a valve.

Of what? If you want to put it on 160M you might manage it, but you are
going to have very poor efficiency.

Figure you want a switching rate less than a tenth of a cycle, if all you
want to do is just reproduce the RF signal. If you want to use the PWM
device to do the modulation as well, you will need to go much faster.

You may want to look at some of the Brown-Boveri AM broadcast transmitters,
which use switching output stages, driven by PWM oscillators that handle
both the modulation and the carrier. The output integrator is a nightmare,
even at 200M.

They are using big switching FETs. You don't really need the sharpest
square wave coming out of the output stage, though, because it's just
producing stuff that the harmonic filter is going to eat up anyway.

There are some very high speed gas tubes out there, like krytrons, but most
of them aren't very high power. The real issue, though, is what kind of
frequency you really want and if you want to do the modulation or just the
carrier with the switcher.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."