[Elecraft] Elecraft KPA500 vs Tokyo Hy-Power 1.1Kfx

[Bob Henderson]

Jim

The ST SD2933 and Microsemi VRF2933 are only superficially similar.

The key differentiator is drain source breakdown voltage, which for the
SD2933 is 130V but for the VRF2933 is typically 180V.

The THP 550fx was designed using SD2933 devices but failures were high.  I
have met several dead HL550fx amps on my trips to the Pacific.  The
THP1.1kfx is essentially the same amp.  THP now use devices marked
THP2933.  I can't say with absolute certainty but I believe these to be
VRF2933.

Running the VRF2933 from a 60V supply is a good idea.  Doing the same with
SD2933 isn't such a good one.

73 Bob, 5B4AGN



Date: Fri, 17 Aug 2012 18:20:39 -0400
From: "Robbins, James" <jsrobbins at earthlink.net>
Subject: [Elecraft] Elecraft KPA500 vs Tokyo Hy-Power 1.1Kfx
To: elecraft at mailman.qth.net
Message-ID: <45B49D8F-BAF4-4B94-81FE-7690A8F9BCC4 at earthlink.net>
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I am wondering if anyone has an explanation for why the Elecraft
KPA500 amplifier (500 watts) employs 2 VRF2933 FETs (Microsemi) in
the final PA where the THP uses 4 ST2933 FETs (STMicroelectronics) to
generate very similar power levels.  The data sheets for each FET
indicate that both brands are rated at 300-400 watts, support similar
mismatches and run at similar voltage maximums.  They have very
similar specs all together.

Perhaps our amplifier gurus could weigh in here.  Much appreciated.

73,
Jim Robbins
N1JR