I agree with the spot-on-the-mark sentiment summary expressed below.
A very fine QRO legal-limit S.S. amp with decent IMD specs can be homebrewed
by the savvy hands-on experimentally inclined (not many of us left?) amongst
the ham radio fraternity.
Jim is right about the complexity and cost of "everything else" particularly
implementing the requisite diplexer based harmonic terminating auto-switched
HF multi-band LPF capable of handling up to 2.5 kW under potentially high
VSWR conditions. In terms of dollars per Watt the modern LDMOS FET active
devices per se are very cheap.
If one is designing a monoband S.S. QRO amp then some complexity and
associated cost savings can be had.
Adequate heatsinking and dealing with the demanding thermal issues (the
Achilles heel of LDMOS and MOSFET RF power devices) and efficient heat
extraction is the other principal challenge. This has a big impact on
semiconductor MTBF.
It can all be done; but not cheaply :-(
Cheap, reliable / good MTBF, no time limit QRO, low IMD, are mutually
exclusive design goals. The pragmatist has to take their pick which
parameters they value most; choosing them all is an expensive exercise even
for the resourceful homebrewer; commercially we are talking over $10K ++ for
a high-end S.S. amplifier.
Leigh
VK5KLT
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Catherine James
Sent: Thursday, 8 December 2016 3:45 AM
To: amps@contesting.com; Jim Thomson
Subject: Re: [Amps] SS amps and auto-tune. Is it even necessary?
On Wed, 12/7/16, Jim Thomson <jim.thom@telus.net> wrote:
## The low cost of the LDMOS is the least of the issues involved. Its
everything else that?s involved with the SS amp.
## Jim VE7RF
Yep, that's it in two sentences. That's why I can't get excited about cheap
SS finals until I see a complete, commercialized SS amp using them, said amp
to be affordable and reliable. Right now they are for experimenters.
73,
Cathy
N5WVR
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