■ Eimac Division of Communications ■ “CRT Still Rules TV Market,”
& Power Industries (CPI), Electronic News, 6/5/2006.
■ Peavey Electronics Corporation,
■ “CRT Not Ready for the Museum
Shelf,” Electronic News, 5/25/2005.
■ Usenet, http://groups.google.com/
■ “Design of a 250MW Hydrogen
Thyratron,” IEEE Pulsed Power
■ Brand X-ray Tubes, www.brand
■ “The Great Krytron Caper,” The
Washington Report, July 15, 1985.
■ Source 1 X-ray Tubes, www.source
■ Nautel solid-state broadcast transmitters, www.nautel.com.
■ Industrial Microwave Systems,
■ Harris solid-state broadcast transmitters, www.broadcast.harris.com.
■ Industrial Microwaves and
■ Nixie Tubes,
as detectors for x-rays and other
ionizing radiation. The most obvious
case is the Geiger Müller tube which
is at the heart of a Geiger counter, but
scintillation detectors also use photo
multiplier tubes to detect the tiny
flashes of light that occur when radiation strikes a radio luminescent crystal.
One of the most interesting applications I came across while researching this article are the so-called “down
hole” instruments used in the oil
industry. Not surprisingly, it’s really,
really hot at the bottom of an oil well
— temperatures at the bottom of a
several miles deep borehole can reach
over 400°F — and, until very recently,
solid-state devices were unable to
survive in this environment. But on the
other hand, Nuvistors — a miniature,
all metal vacuum tube invented in the
1950s for UHF applications — can
operate up to 500°F or more.
Nuvistors were used in down hole
instruments up into the 1990s and
have only been supplanted by solid-state devices in the last decade.
I wanted to end by saying that
vacuum tubes would be with us
forever, but it’s not that simple. Many
of the applications I’ve mentioned are
slowly but surely being overtaken by
solid-state devices. LCDs are steadily
replacing CRTs, and it won’t be that
long before CRTs disappear.
There are already several, completely solid-state MW/SW broadcast
transmitters in the hundred kilowatt
range, and there are a number of solid-state alternatives to TWT transmitters
for satellite links. The latter are generally much lower power than their TWT
ancestors — transistors are still not good
for high power levels at microwave
frequencies — but for satellite Earth
stations, the gain of a 10 meter dish
obviates the need for lots of power.
Even the guitar players may switch
eventually — Peavey engineers have
studied gain, response, compression, and
several other factors that create the “tube
sound” and have come up with a line of
“Trans Tube” all solid-state amplifiers.
But there are still some applications
that are safe for the foreseeable future.
For one, nobody has come up with an
X-ray LED (at least not yet!). And it’s hard
to imagine how a solid-state replacement, even if one existed, could be
simpler or more reliable than the magnetron in your microwave oven. NV