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from the my-vacuum-has-a-bag-not-a-tube dept.
More than a half century later, traveling-wave-tube amplifiers still dominate satellite communication. That's right—your ultrahigh-definition satellite TV and satellite radio come to you courtesy of vacuum tubes in space.
Of course, there's a huge difference between Telstar's 3.5-watt, 4-gigahertz amplifier and one of the dozens of highly efficient microwave amplifiers on, say, the DirecTV-15 satellite, launched earlier this year. The latest generation of traveling-wave tubes can provide up to 180 W at frequencies up to 22 GHz, with efficiencies approaching 70 percent and rated lifetimes exceeding 15 years. Though their basic function is the same—amplifying RF signals—just about everything else has changed: the design, the testing, the materials, and the fabrication.
...
And now, ongoing research into a new and potentially revolutionary kind of traveling-wave tube—the ultracompact and ultraefficient cold-cathode TWT—looks poised to deliver the first practical device by the end of this decade. These are exciting times for vacuum tubes. Here's why.
No cheating this time--read the article to find out why.
(Score: 0) by Anonymous Coward on Friday November 27 2015, @09:45PM
Class A - The device is conducting all the time, deviating from its Q point, up and down its load line.
This is the least efficient amplifier configuration.
Class B - The device is conducting 50 percent of the time.
The active devices are typically used in pairs (push-pull), with each half handling half the waveform and the halves are added (typically with an output transformer) to increase the output voltage swing.
Class AB - The device is conducting slightly more than 50 percent of the time.
This gets rid of "crossover distortion" at the zero-volts part of the waveform.
There have been tons of audio amps built using a pair of 6L6s in a push-pull configuration (and a big honking output transformer).
Class C - The device is conducting less than 50 percent of the time.
(It spends most of its time in the Off state.)
In RF circuits, you hit the circuit with what is effectively a pulse and you let the circuit "ring" for the rest of the cycle at the resonant frequency which you have selected via the physical dimensions of the passive components.
(At "lower" frequencies, those are inductors and capacitors; at higher frequencies, waveguides are used.)
Class C is the way to get high efficiency.
Class A is the complete opposite.
.
their resilience to error
That's the big one right there.
In a previous life, I repaired electronic organs.
Take a church that is in the middle of nowhere and give it a spire that is the tallest thing for miles and miles.
It is going to get hit by lightning, no 2 ways about it.
Now, put an electronic organ in it and have an organist who doesn't leave it unplugged when not in use.
Their chances of having to call me were greatly diminished if it was built with tubes.
-- gewg_