Art Greenberg wrote:
On Sat, 16 Jun 2007 02:27:09 -0500, Tim Daneliuk wrote:
Even so, semiconductors never completely replaced vacuum tubes. Radio
transmitters of any large size still use tubes (valves to those of
you in the rest of the Anglosphere) because there are no transistors
of which I am aware, at least, than can deliver 50KW of RF into an
antenna.

High-powered radar has been all solid state for some time. Many, many
peak KW at low duty cycle into the antenna. Continuous (AM, FM, TV) at
high power uses a number of smaller amplifiers with a split feed at the
input and a combiner at the output.

Back in 1975, I worked with solid state amplifiers in the ultrasound
range (30-50KHz) that delivered bursts of a single tone into a piezo
transducer. Several peak KW with two TO-3 transistors and no heatsink!

Today, Harris Broadcast sells an all solid-state 40KW FM broadcast
transmitter. I'm sure there are others, and for AM and TV as well.


Interesting. I used to service marine Radars, and while their peak
output power was in the 10-50 KW range, their average power was far
lower because of the low duty cycle. When you say that radars have
been solid state for some time, does that mean magnetrons and klystrons
are no longer in the picture? (Not arguing, just curious.)

--
----------------------------------------------------------------------------
Tim Daneliuk
PGP Key: http://www.tundraware.com/PGP/