RE: The toob finally sets...

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 

At 07:51 AM 9/13/2004 -0600, you wrote:
>Original poster: "David Trimmell" <humanb-at-chaoticuniverse-dot-com>
>Jim is completely correct. It is amazing what Si devices are up to but
>you cannot beat a vacuum for hardiness. Certainly the solid state is
>most energy efficient in lower power, but higher I don't know. Jim, just
>curious, but where did you get your efficiency comparisons from?

The efficiencies were for power amplifiers in space applications. For lower 
frequencies, solid state is MUCH more efficient than 20%, particularly for 
constant envelope applications. Look, for instance, at Rutledge's work at 
CalTech on Class E amplifiers (85-90% efficiency) using cheap FETs at 7 
MHz. There are some folks getting this kind of efficiency at microwave 
frequencies, but it's at low output powers (<1 Watt).  There is enormous 
interest in getting efficient PAs for the wireless telecom industry, since 
the transmitter PA in a cellphone is a big chunk of power consumption.

In microwave amps the power converter from bus voltage to using voltage can 
have a huge effect on overall efficiency.  In a typical TWT, you'd have a 
power converter to make the HV (and filament power) that runs around 
80-85%.  The tube itself is fairly efficient too, also in the 65-70% range, 
so the overall package runs around 50%.

Solid state amps (linear) run in the 30% efficiency range (biased Class A 
or AB)


>It
>would beinteresting to really compare the relative efficiencies bellow
>1 MHz. There is something about a nice hot vacuum tube; they do heat a
>cabin well in the winter!
>Not too sure if it would be even conceivable to design a comparable
>circuit of the current DRSSTC with a VTTC without becoming even more
>complex (multi stage, etc.)? But if possible you wouldn't have to worry
>about "exploding" Si packages, only the silent death of melting plates!

Or softening seals.....


>Regards,
>
>David Trimmell