[Amps] Can I cool too much the tubes or ants?

[Glen Zook]

Back in the late 1960s some of the technicians at the Collins Radio plant here in Richardson, Texas, were testing one of the military amplifiers, 308-U20, that put out at least 20 kW.  This particular amplifier has an auto-tune that can definitely match a very wide range of input impedance.

The technicians placed about 100 feet of wire across the parking lot and then activated the amplifier.  They soon noticed that the end of the wire was burning.  Someone got the idea to just let the amplifier operate and see how long the auto-tune would function before shutting down the amplifier.  The wire continued burning until it was less than 3 feet long when the safety circuits shut down the amplifier.

Those same technicians liked to check out the 3 MHz to 30 MHz Collins built log periodic antennas using the "CB" channel 19.  Since Collins was building antennas for the military the technicians were authorized to operate on any frequency within the range of the antenna.  So, CB channel 19 was one of the frequencies that they liked to use.  The system consisted of a KWM-2A and one of the 20,000 watt amplifiers into the antenna.  This resulted in an e.r.p. of around 200,000 watts.

A test transmission involving both a carrier then some voice would be made.  Then the technicians would just listen for a minute, or two.  Virtually every time the frequency would be silent for several seconds.  Then, someone would come on the frequency asking "WHAT WAS THAT"!  The technicians would then make more test transmissions on Channel 19 which "stirred the pot" even more.  Finally, the technicians would change to other frequencies within the range of the antennas.

Glen, K9STH

Website:  http://k9sth.com


--- On Mon, 8/23/10, Jim Thomson <jim.thom at telus.net> wrote:

Melting antennas is a very good sign since I am the last one to relate this story.
 
Circa 1957. San Fernando Valley, CA W6HX, Ted Gillete builds a 20 meter amplifier for W6YMD using 2-- 4-1000D tubes. They run 7000VDC on the plate at 2 Amps. This causes the driven  element to glow at the ends as neighbors knock on Bill's door to tell him there are invaders from outer space. Actually they worked many AP, VU, & 3B8 that night. The antenna did not survive. Anyway that's what was relayed to me.....