This is a photo, from about 1935, of the RCA-50B 50 kW AM Broadcast Transmitter installed
at station KOA in Denver. The RCA-50B Transmitter was installed by many Class 1A 50 kW
clear channel stations during radios golden age in the 1930's. NBC's owned
and operated stations in Chicago, Denver, New York, and San Francisco, all used the
RCA-50B transmitter. NBC's RCA-50B transmitters, installed in the 1930's, remained in service
until they were replaced in the early 1960's. The 50B transmitters were manufactured
for RCA by the General Electric Company, and the Westinghouse Electric and Manufacturing
Company. An article describing the RCA-50B Transmitter can be found in the
October 1930 issue of the Proceedings of the Institute of Radio Engineers titled,
"Some Developments In Broadcast Transmitters". The 50B transmitter consisted of a 50 kW
linear amplifier using two water cooled UV-862 tubes in a push pull circuit, which was
driven by an RCA-5B 5 kW transmitter. As can be seen in the photo of the 50B installed at
KOA, the 50B consisted of 4 main units. The panels in the left side wall are the 5 kW
driver transmitter. The panel on the left side of the rear wall is the 50 kW linear
amplifier, while the panel on the right side of the rear wall is the main rectifier. The
control panel is on the right side wall.
This is the RCA-50B transmitter at WENR in Chicago as it appeared in a 1932 photo.
The 50 kW linear amplifier of the 50B appears at the right rear, while the control
equipment for the transmitters appears to the left in the photo. WENR's RCA-50B
was later replaced by a new RCA-50D, and WENR's old 50B was moved to WEAF's new Port Washington site in 1940.
The Rectifier for the WENR 50B is at the center rear in this 1932 photo.
An older transmitter of open construction appears behind
the railing on the left, and in the rear of the photo adjacent to the rectifier for
This 1932 photo shows WEAF's first RCA-50B transmitter which was installed at Bellmore Long Island.
This transmitter remained behind at Bellmore to maintain continuity of service while WEAF moved
to their new Port Washington Long Island site in 1940.
This 1940 photo shows the old WENR RCA-50B 50 kW AM Broadcast Transmitter as it looked after
it was installed at WEAF's new Port Washington site in 1940. It can be seen that WEAF's
"new" RCA-50B has been dressed up with stylish modern trim. Only the 50 kW linear
amplifier and rectifier were moved from Chicago to New York. WEAF used an existing spare 5 kW transmitter,
with extensive modifications, to drive the 50 kW amplifier. Over the years most
50B transmitters underwent similar modifications to upgrade their performance.
The control panel was installed between the 50 kW
linear amplifier and the main rectifier, rather than the typical location to the right of the main rectifier.
NBC eventually changed the call letters of station WEAF to WNBC. To see how RCA
and NBC converted WNBC's RCA-50B transmitter for AM Stereo operation in 1959,
This is the RCA-50B 50 kW AM Broadcast Transmitter installed at station KPO in
San Francisco. As can be seen, KPO's installation of the 50B is very similar to that
This is the first RCA 50B which was installed in 1929 at WTIC of Hartford.
It was known by RCA engineers as "Number One" of its type, and was the first
high power commercial transmitter to use 100-kilowatt tubes, the first to use
mercury-vapor type rectifiers throughout, and the first capable of 100 percent
modulation of its full rated 50-kilowatt carrier output. Notice the RCA logo
on the main rectifier cabinet in this 1930 photo.
This is a view of the 50 kW linear amplifier cabinet for WTIC's "Number One",
with the doors open to show the two water cooled UV-862 tubes.
This is a close-up view of the Main Rectifier cabinet for WTIC's "Number One"
50B Transmitter, showing the RCA logo.
Thanks to John Schneider for the photo of KPO's RCA 50B Transmitter. You can learn
more about the history of KPO on John's web page:
Thanks to Jim Hawkins for the photo of WEAF's first RCA 50B Transmitter. You can
learn more about WEAF's successor on Jim's web page:
WCBS/WFAN Transmitter Tour.
I would be interested in hearing from anyone that has any additional information on
the RCA 50B Transmitter. I am especially interested in finding a photo of the RCA 50B
transmitter installed at WMAQ in Chicago, and a copy of the Instruction and Operating
Manual for the RCA 50B Broadcast Transmitter.
I can be reached by email