On 08/19/2011 07:05 PM, Roger (sub1) wrote:
>
> I really don't see wide adoption of SS legal limit amps until the
> devices can be made more rugged, can be cooled more easily, and become
> available at much lower prices. Prices are based on tooling set up
> costs, number of units produced per batch, amount of silicon in the die
> compared to the base wafer size, and yield efficiency. At present they
> are just too fragile and the protective circuitry (which is more
> complicated than the amp) really pushes the prices far too high for wide
> spread adoption.
I used to think the same thing...but not any more.
The Freescale MRFE6VP61 can withstand 60:1 VSWR for 10 msec, which is plenty of
time for a simple controller to shut it down. That part costs $271 for about
1000W out...a lot cheaper than a 3cx800. Transistors will get cheaper. Tubes
will get more expensive.
The commonly used reference design for the amplifier uses a large block of
copper to spread heat into a large Aluminum finned heat sink. But water
cooling
makes better sense. Mount the transistor to about a 1/2 inch square water pipe
to minimizes the thermal path from transistor to water and use the water to
spread the heat rather than a lot of heavy expensive machined metal.
Transistors dump heat at ground potential while tube dump heat at high DC and
RF
potentials. That makes cooling a LOT easier.
The cooling system becomes a transistor mounted on a short length of square
pipe
that has some hoses leading to a bucket for thermal mass or maybe a fan cooled
heat exchanger.
I'm designing a transistor control board that uses a FET to switch the 50V
drain
supply. The micro-controller cuts off the amp in about 2 msec on any fault
conditions. The FET doesn't need protection from drive without supply voltage.
Homebrew amps can use a 3000W supply available on ebay for $25. Commercial
manufacturers will have to pay real money for a switcher, but you get power
factor correction, light weight, and huge volume discounts because lots of
supplies use the same components.
The trend from 12V to 24V to 50V supply has greatly simplified output network
design because the device output impedance goes up by 4 for every doubling of
supply voltage.
Total amplifier size will shrink and become separate subsystems, especially
with
water cooling. Amplifier pallet smaller than a paperback. Power supply
smaller
than a shoe box. Water cooling smaller than a bucket. Control box just large
enough for a meter and display.
Multiple amplifiers can share the subsystems. Parallel power supplies for more
capacity. Routing 50V around the shack makes more sense than routing 4 kV.
Multiple amps can share the same water cooling bucket. Multiple amps can share
the same controller.
jeff, wa1hco
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