[AMPS] Class E MOSFET Amps

[Steve Thompson]

In message <35470FAE.6C7DF1AA@erols.com>, Mark Hall <markeh@erols.com>
writes
>Hi all:
>
>I'm new to this archive and have built a somewhat figity 4-1000
>amplifier over the past couple years.  Almost afraid to "fire" it up
>because the plate gets so bright red/orange.  4.5 KV scares the heck out
>of me and more than a couple times I've heard a loud "SNAP" from the
>darned thing.  It keeps cranking nevertheless.  It's no beauty, but does
>the job.  I've been looking for info on Class E solid state amplifiers
>and was wondering if anyone has experimented with or built one.
>Primarily interested in 7 through 21 MHz which should be possible
>without resorting to $100+ Motorola  MOSFETs.  Any clues to this elusive
>animal would be greatly appreciated.
>
>'73  KI4Z

Class E operation relies on a couple of key points to deliver the high
efficiency - the device has to be able to switch very quickly compared
to the rf cycles going through it, and the external load (your antenna)
has to be matched quite precisely to the device. You will need a
separate tuning network for each band.

I doubt that you will find cost effective devices with the switching
speed needed for 21MHz, and if your antenna tuning is not perfect, there
is a great risk of destroying the devices.

Class E amplifiers are not linear - you can't easily put SSB through
them.

If 2.5kV is less scary, you might consider 4CX400s, or 3CX800s if you
have the drive.

Steve

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