[Amps] Advice needed for SS amp

[Paul Decker]

Hi Bill,
I had an amp using the MRF1500 parts, based on the commercial  Tokyo high power design.   

I also talked to the THP guys for a while at Dayton and they are phasing out their ARF1500 design using the Microsemi.  The reason I was told is because of quality issues with the parts themselves.

IMHO, it may be better to go with the NXP BLF578XR since it is a 1500W part although it is only 50V.

Paul,
kg7hf



Message: 1  Date: Wed, 05 Jun 2013 09:07:14 -0700  From: Bill Turner   To: Amps   Subject: [Amps] Advice needed for SS amp  Message-ID:   Content-Type: text/plain; charset=us-ascii	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