Let me chime in on this thread:
As semiconductors have improved over the last half century, they have
progressively replaced, displaced, and ruled out tubes that formerly
were used instead of them. Keep in mind that around 1950 tubes were used
even in computers! But as solid state devices become available that
replace tubes with advantages, the tubes that were replaced are no
longer developed. There is no market for them, so why should anybody
invest in development?
The same trend will surely continue. Solid state devices will continue
to be improved, and this will phase out tubes from some of the areas
where they are still dominant. I can very well envison that HF
transmission tubes in the 100 watt class will soon be available only as
collector's items (we are pretty close to that already!), while HF tubes
in the 1kW class will continue to be manufactured for some more years,
but not developed further, while tubes for the 10kW plus power classes
will continue going strong, and even be improved, for some longer time.
It's all a matter of performance versus cost.
Maybe somebody comes up with a novel idea that gives empty state
technology a new boost. And maybe somebody comes up with a breakthrough
in solid state technology that gives even high power tubes their last
blow. And maybe someone comes up with a completely new technology that
puts both tubes and MOSFETs to rest. It's your collective guess what's
most likely to happen! But significant development, which demands large
amounts of money, will surely be put only into technologies that seem to
have a profitable market. And I honestly doubt that HF communications in
the 1kW class are a market attractive enough to warrant much investment
by the big companies. A big sign written on the wall is that the newer
high power MOSFETs are typically VHF and even UHF devices, not HF, aimed
at FM and TV broadcasting, or more commonly are aimed at medical and
industrial applications rather than communications!
Who knows, perhaps in a few decades we poor few remaining stubborn
little hams will have to make our power devices at home! THAT might
indeed lead to a renaissance of tubes! It certainly seems more possible
to make a tube at home, than a MOSFET...
More likely, we will have to transmit using devices made for arc welding
and nuclear magnetic resonance imaging, pressed into linear amplifier
service... Don't forget that a few decades ago, the most common HF power
devices used by hams were tubes optimized for the horizontal sweep
function of TVs, of all things!
Manfred.
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http://ludens.cl
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