I'm thinking of building a solid state 1500 watt amp using some of
MicroSemi's high voltage MOSFETs. This is a new kind of project for me and I
would appreciate any comments you might have which would help me avoid any
blunders.
The MicroSemi ARF1500 looks attractive because of its high power
capabilities and relatively low price. Digi-Key carries these for $205 each.
A single one is rated at 750 watts output so I would use two of them. I'm
thinking of water cooling.
MicroSemi data sheet is at
http://www.microsemi.com/existing-parts/parts/81770 and there are other
versions with similar ratings.
Notice the unusually high power supply voltage. I'm thinking of running a
full wave bridge rectifier directly off the 240 VAC line, thus eliminating
the power transformer and giving about 340 VDC no-load. The amp would have
to be isolated from ground of course, with input and output coupling via
toroid transformers and PTT switching done by a well-insulated relay.
A set of four 10 amp 600 PIV diodes is available on eBay for less than $30
and a 6800 uF 450 VDC capacitor is available for about $50 including
shipping. There's most of your power supply. Pretty cheap, huh? :-)
Of course with that size cap a step-start circuit would be mandatory lest
you blow your main house breaker when you power up.
My main use would be RTTY and CW so linearity is not an issue, but do you
have any thoughts on what the IMD might be for SSB? I can't find any data on
MicroSemi's website for that. Maybe it's no good for SSB.
Since the output impedance is about 50 ohms, I'm wondering if a 1:1
broadband antenna balun might serve for the output toroid? Just a thought.
Might not be a good idea.
Like I said, I'm a complete newbie at solid state amps so all comments are
welcome. This almost seems to be too easy to be true. Go ahead, burst my
bubble. :-)
73, Bill W6WRT
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