some what of a Segway, is tubes for AC->DC->AC transmission. That segment had
converted to SS quite some time ago.
-pete
On Tue, Aug 16, 2011 at 11:01 AM, John Lyles <jtml@losalamos.com> wrote:
> Ignoring more exotic tubes like gyrocons, gyrotrons, TWTs, relativistic
> electron devices, things that the Naval Research Lab is doing, there is
> still vacuum tube improvement being done in the industry. Notice that I
> didn't say research. As broadcasting and wireless has pretty much
> embraced silicon devices (except for HF transmission at high power),
> advances in power tubes are being made to support more demanding
> applications such as scientific and military needs. Not amateur radio
> and not AM/FM radio. Ham radio saw the peak of development 20-30 years
> ago, although occasional variants of old tubes are introduced for
> specific targets, like the somewhat successful 3CX1200 introductions
> from Eimac that were supposed to replace glass 3-500Z sockets as well as
> 8877s. There are others too, that hams embrace here. Television has
> converted to solid state where it is feasible, although IOTs (a linear
> beam tube with a grid) have held ground in UHF for higher power due to
> simplicity and lower cost.
>
> IOTs, klystrons (multi gun/beam) and gridded tetrodes are still being
> designed for various projects, such as resistive heating sources for
> fusion machines and as sources for RF particle accelerators. There are
> many accelerators built and planned to be built worldwide, serving
> industrial to basic science applications. Not just big bang machines
> like LHC at CERN.
>
> Techniques like multiphase cooling (Hypervapotron is one mfr's name) to
> exchange anode heat with water at much higher efficiency, pyrolytic
> graphite for grids, and improvements to cathodes for higher loading are
> all improvements that are working their way into big tubes. These make
> tremendous increases in power density. In cathode loading, a tube with
> thoriated tungsten (going back to Langmuir and others at GE) can deliver
> as much as 3 Amps per cm^2 of electrons in a well designed tube to get
> lifetimes > 20,000 hours. Figure the size of the filament basket and you
> understand how the peak current can be 1000 amps overall. Thats just not
> possible in a transistor junction, no matter what type. Combining lots
> of transistors gets there, however, at a cost.
>
> For example, the TH628 from Thales has over 1 MW plate dissipation, with
> less water flow and high performance into the VHF. The 4CM2500KG from
> Eimac has over 2 MW plate dissipation, with slightly lower frequency
> ranges but very high CW power. I wouldn't say that the few remaining
> tube manufacturers are sitting still, but they are not cranking out new
> designs yearly either. They are making measured step improvements to
> their existing products, a lot easier than starting over with a clean
> page. These two examples are sort of the crowns for these two companies
> to push performance limits.
>
> Others mentioned cold cathode research with field emission and such.
> Metal filament and oxide-type tubes and cathodes provide excellent long
> life performance, if properly rated for the application. It's when
> engineers try to exceed the ratings that lifetimes shorten. Or
> manufacturers reduce quality (rising gas levels for example). Similar
> lifetime-reductions happen in solid state devices when application
> demands more than the device designer expected, except much quicker -
> flash, pop.
>
> As a designer of power amplifiers using both tubes and transistors, I
> see a good trend in solid state, with 1200 watts or more per device. But
> I don't expect to see a megawatt in a device, something that I can and
> do see with new tubes. Ham radio will eventually quit using tubes except
> for nostalgia reasons; we are still seeing a few 304TL and 450TH
> amplifiers getting built due to having the parts and for fun. As long as
> their is a market, the Far East will provide bottles for building simple
> amplifiers. Don't expect any new tubes for this, however. HV power is
> getting harder to come by due to cost of iron and copper. Switch mode
> technology comes just in time.
> 73
> John
> K5PRO
>
> N7CXI wrote:
> > This discussion of "super semis" makes me wonder if anyone is still
> > engaged in vacuum tube research these days. Could any of the basic
> > tube wear points be improved on with modern technology? Could
> > filaments be made to emit twice as long without degradation?
>
> > I just looked at the CPI Eimac site and I can't see where they're
> > motivated or have the resources to innovate at the basic level. They
> > list "Amateur Service" as a product category, which can't bode well
> > for volume sales... Assuming MOSFET technology passes tubes by at
> > high power levels, will they just go quietly into the night?
>
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