this August 1947 image, Walter F. Myers, chief engineer of WJJD(AM) in Chicago,
is checking the meters of his station’s brand new RCA BTA-50F 50 kW transmitter.
was the first post-war 50 kW unit delivered by RCA, at a cost in excess of
$250,000 (more than $2.5 million in today’s dollars).
completing its power increase from 20 kW to 50 kW, WJJD became Chicago’s most
powerful independent station. The station owner at the time was Marshall Field,
the Chicago department store magnate.
operated with 50 kW on 1160 kHz as a daytime-only station, signing off at
sunset to protect clear-channel KSL in Salt Lake City. WJJD started
broadcasting full time in 1980 and is now known as WYLL.
high-level plate-modulated BTA-50F replaced the pre-war BTA-50E and utilized
new technologies developed by RCA during the war. Its impressive lineup of six
cabinets, painted in RCA’s signature glossy umber gray, filled up an entire
wall, including the front-entry door which provided access to the inside of the
transmitter. Separate rooms in the transmitter building housed the
transformers, blowers and AC control circuits.
BTA-50F was the first high-powered transmitter to use air-cooled tubes,
utilizing two RCA 9C22 modulators and two more as finals. Additional tube
sockets were provided for three hot-standby tubes. A hand-operated forklift was
used to change the tubes. The transmitter consumed a breath-taking 156 kW at 90
of the BTA-50F started 1947. In addition to WJJD, the first units went to KOMO
in Seattle, WCFL in Chicago and WFAA in Dallas. Because of its excellent sound
quality, KOMO kept theirs on the air into the 1990s.
June 1947 issue of the RCA Broadcast News featured an extensive promotional article about the BTA-50F.
John Schneider is a lifelong radio
history researcher. Write him at email@example.com.
This is one in a
series of photo features from his collection. See past images under
Columns/Roots of Radio at radioworld.com.