The Fifty Kilowatt KGA Transmitter in Southeast Spokane on Moran Prairie.
by Val Strange, Chief Engineer
"It was the long time ambition of Mr. Louis Wasmer to run a 50 kW transmitter, as was the desire of many station owners. Soon after the war was over in 1945, the government started to dispose of its surplus war material, which included this RCA 50 kW AM transmitter. (NOTE: FCC records of 1942 show that KGA, in a construction permit, proposed to install an RCA BTA-50F transmitter.)
"This transmitter was built to be installed in Italy by the Radio Corporation of America and was their most recently designed high power transmitter to be used in connection with the campaign in the war with Italy and it was transported to Italy, but it was never set up and used as the armed forces were far ahead of the predicted schedule. The transmitter was not even unpacked. Later on, it was shipped to Argentina and soon after it was delivered, they found no need for it and it was declared surplus and advertised for sale. Mr. Wasmer was able to buy this fine transmitter at a most reasonable price and had it shipped to Spokane and installed it with the directional antenna system of two elements of 365-foot guyed towers and fed with the then popular open wire configuration of transmission lines. Apparently the main problem was to have a clear channel for 50 kW operation assigned and the recent 1510 kHz was the only one available, and while it does work well in high conductivity earth due to the rapid attenuation at high frequencies, it did not do as well as Mr. Wasmer had hoped it would. Mr. Chronic relates of the hectic times in operating this transmitter on the 1510 kHz channel and efforts to cover the Eastern Washington service area as they felt a 50 kW transmitter should. The station was known world wide for transmission to distant countries and ships in the Pacific, but coverage to the Eastern Washington area was not what he had desired...
"The RCA fifty kW transmitter was basically a 5 kW transmitter using 892R air cooled tubes operating as drivers to the final amplifier and the high level modulators employing the large air cooled tubes, 9C22. The 892Rs of the driver operated at 8,500 volts and the final amplifier and modulator operated at 10,000 volts from a 3-pahse full-wave rectifier using 857B mercury vapor tubes. The station operated with one antenna daytime non-directional and nighttime directional with two towers in the antenna system. The antenna pattern gave minimum radiation to Memphis (sic), Tennessee.
"This RCA type 50F was one of the first large transmitters to operate without water-cooling. The 892R tubes were made up of 892 water cooled tubes with radiating fins to the external plate for dissipation.
"A pair of 9C22 tubes was used as final amplifiers and a similar pair was used as high level Class B modulators. All of components of a high power transmitter are large and heavy. The power supply, the driver and modulation transformer were in the 1000-pound class and the 9C22's were over 100 pounds each. The 9C22's were later replaced with an improved 5671 type. Up until this transmitter was developed, large transmitters employed water cooling on all tubes. The 10,000-volt rectifier, which used the 857 mercury vapor tubes, was modernized to the new solid state type using silicon diodes. The diodes were more reliable as they did not flash-back as mercury vapor tubes did. KGA has a fine well designed transmitter."
About Chief Engineer Val Strange
Val Strange was chief engineer of KGA from 1949 to 1968. (NOTE: Although Mr. Strange was not the chief engineer when KGA first moved to this site, he had first hand knowledge about the workings of the transmitter and he would have had access to people who were involved with the initial installation.)
The above article appeared in Partlow's and Jorgenson's "Early History of Spokane Radio."
compiled and editted by Bill Harms - 30 May 2007