Barry Mishkind - The Eclectic Engineer
Last Update 6/27/09
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The tube featured on this page is a Western Electic 320A. They were used in a custom high power transmitter built by James O. Weldon of Dallas, Texas, for XERA, a Mexican station along the border with Texas.
You'll notice the tube is taller than the doorway next to it, approximately 8 feet tall. The text from the two plaques (on either side of the tube) contain the attached text, "carefully transcribed" by David Hershberger, who also kindly supplied the picture.
WESTERN ELECTRIC TYPE 320A
HIGH POWER TRIODE
Eight of these tubes were put into service in 1938 in the 500 kilowatt transmitter, XERA, at Ciudad Acuna, Mexico, designed by Jim Weldon.
The tube was developed by Bell Laboratories in 1937. The design engineer was Doctor H. Eugene ("Dick") Mendenhall, who was present at the site during initial tests.
The high efficiency "Doherty" linear power amplifier was used in each of the two 250 kilowatt amplifiers which were parallel combined.
Mr. William H. Doherty inspected the installation about a week or so before preliminary testing started.
Only nine of these tubes were ever built and no tubes ever failed in service nor during the four years operation which followed before the station was closed down. It has a "bright tungsten" filament (no thorium).
A crack in the lower glass was found to have occurred in one tube during the day's idle period and none of the Mexican janitors could remember hitting it with a broom handle.
James O Weldon
Weldon was born in Canton, Missouri. He attended Culver-Stockton College where his father taught. His early interests included radio. After studying at the University of Nebraska, he took full time jobs as a radio station engineer from 1927-1935, beginning in Topeka, Kansas.
At KFKB, Milford, KS, Weldon became associated with Dr. John R. Brinkley, who sent him to Villa Acuna, Mexico in order to increase the power of his station, XER, to 100 kilowatts. In 1938, the station (now XERA) was increased to 500 kilowatts, only the second such station in the western hemisphere. XERA, was the first to use the "Doherty Amplifier" at this power level.
In 1940, Weldon was consulting the Federal Telphone and Radio Corporation, designing and building several of the 50 kW radio stations in the New York City area.
Following WWII, he became a partner with Lester Carr ("Weldon & Carr") in doing antenna design and general practice before the FCC. Carr specialized in super-power antennas and Weldon in high power transmitters. In 1946, he arrived in Dallas, and organized what would become Continental Electronics. The current facility was opened in 1951.
One of the first projects was a 1 megawatt MW transmitter (105-B) developed in competition with RCA for the USIA. The transmitter was installed in Munich.
Weldon retired in 1988, but continued visiting the plant right up until his death.
--- The picture and biographic information was adapted from The Continental Courier of May, 1993
Tube Data Sheet
320A Vacuum Tube
The 320A Vacuum tube is a 3 element water cooled tube designed for use as an oscillator, modulator, or amplifier at the higher power levels and high frequencies.
Filament ratings: 35 volts at 435 amperes
Average thermionic emission: 90 amperes
Characteristics at 18 kV plate voltage and 8 amperes plate current
Amplification factor: 30
Maximum plate ratings:
maximum plate voltages:
current: 15 amps DC
dissipation: 150 kilowatts
The 320A vacuum tube must be mounted vertically, with the filament terminal end down. A plumb bob should be used for vertical alignment.
When a standard socket or mounting is not provided the following mounting suggestions should be adhered to. The tube should be supported from the under side of the upper bulged section of the water jacket. Care must be taken not to deform the water jacket by clamping.