Paul G. Allen wrote:
James G. Sack (jim) wrote:
Is it not true that tubes are still the kings in the (ultra-) high power
arena -- eg rf transmitters.
Yes, it is true.
Agreed, but power MOSFET's are starting to make inroads.
http://www.elecdesign.com/Articles/ArticleID/11057/11057.html
"High-power broadcast-TV transmitter design should become easier with
the MRF6P3300H enhancement-mode MOSFET. Designed for use in TV
transmitters of 1, 5, and 10 kW, it can dissipate up to 300 W. It's the
next generation of Freescale Semiconductor's high-voltage, laterally
diffused metal-oxide semiconductor MOS technology (LDMOS).
The n-channel device can be used in the 470- to 860-MHz range as a
push-pull class AB power amplifier. It can be operated from a 32-V
supply. Also, it delivers a power gain of 19 dB with an efficiency of
57.5% at 300 W. With these advances, fewer devices are needed to make a
multi-kilowatt power amplifier. The leadingedge thermal-management
approach enhances the MOSFET's efficiency, too."
The primary advantage to MOSFET's is reliability. You don't have to
worry so much about powering the tube gradually to preserve the filament
or worry about the filiament lifetime.
The primary disadvantage, as I understand it, is resilience to lightning
strikes. Tubes can apparently take a strike and keep working; MOSFET's
die a horrible death.
-a
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