RCA Equipment Archive

From the time RCA was formed (using the combined engineering of Westinghouse, AT&T, Marconi and GE), the company was a formidable source of broadcast gear. The last 50 kW unit was shipped in 1977. In 1985, GE bought RCA and dissolved it.

50A
The first 50 kW unit by GE for RCA was the 50A. Reportedly, only one was made in 1927, for WEAF.
	From an old magazine. Notice the tubes are exposed, and the railing is to keep the operator from the high voltage.
The 50A and 50B used motor generators to run the transmitters on DC, the later transmitters ran on AC. All together the transmitter used 20 UV207 tubes for audio and RF. Modulation was high level Heising modulation.

50B
The 50B was built, starting in about 1927 or 1928. This was Heising-modulated, linear-amplified, and water-cooled. One of the earliest practical 50 kW transmitters, 50Bs were in daily use for over 30 years.

	The KFI RCA 50B, installed in 1931, and featured in the RCA Broadcast News
The 50B had a 250 Watt exciter, followed by a 5 kW IPA to drive the UV862 finals.

50C
The 50C seems to have been an upgrade from the 50B, and the first design changes by RCA. The filaments were changed from DC to AC and the final tubes were changed out.

50D
The 50D was produced starting in 1937. It was the first truly RCA design: a Doherty-style modulated, water-cooled unit. However, since David Sarnoff did not want to pay royalties to Western Electric (for a 90-degree lagging network between the tubes), his company developed the "RCA Class B-C High Efficiency Linear Amplifier." This was a 270-degree network, to get past the legal niceties. Apparently it did not work, as legal hassles continued. A total of only six 50-D's were made. They were installed at KNX, Los Angeles, WLS, Chicago, WWL, New Orleans, WCKY, Covington, KY (Cincinnati), WWVA, Wheeling, WV, and CBA, Sackville, New Brunswick, Canada. The last of these were said to have been scrapped in the 1970s.
	The 50D was available in two layouts, a "flat" layout and a "U" shape.
Being the operator for this transmitter must have been as close to operating a spaceship as you could get in those days!

BTA-50E
The 50E was introduced in 1941. It was a plate modulated transmitter. The first 50E delivered is said to have gone to KOB in Albuquerque, NM. Reports are that only a half dozen or so "E"s were built, with other US units going to KTRH (Houston), WCAU (Philadelphia), and KGA (Spokane, WA). According to reports, one went to the Aspidistra project and several were in use for the BBC's "Light Programme" on 1214 kHz.
	Now on display in Tommy Bolack's Electrical Museum in Farmington, NM, KOB used this transmitter from 1941 until its removal in 198x.
This 5/10C was the exciter/driver for the 50E. It also lives at the Bolack Museum.
	Although it looks brown due to the monochromatic photo, KTRH's 50E was also blue/green like KOB's. Courtesy: Bruce - Houston radio history blog

BTA-50F
The BTA-50F was produced starting in 1947 (it was after WWII that RCA added the BTA ... presumably to avoid confusion with the new BTF FM series). This was also a plate modulated transmitter. The upgrade to the "F1" series was the following year, using a thoriated tungsten filament 5671 tube for higher efficiency. (The "F"s were upgraded to "F1".)

	KOMO in Seattle used the 50F
The 50F Power Amplifier Tube compartment
	The 50F even had a door that you could walk through to get into the transmitter from the front. Here, the door to the power supply section is open.
KRMG in Tulsa installed a BTA-50F1

BTA-50G (1954)
The 50G was the first Ampliphase transmitter. (Ampliphase was RCA's trademark for outphasing modulation, and was based on the Chiriex design from France, implemented by engineers at McClatchey's KFBK in Sacramento.) Two 4-250s fed a pair of 5762s, which drove the 5671s that were used as PAs. Production began in 1954. According to one source, about 30 were built.


BTA-50H (1961)
The 50H was the second generation Ampliphase, starting in 1961. The IPAs were changed to 4CX5000As and the PAs were changed to 6697 triodes. The price in 1961 was $99,750
	From an RCA spec sheet
	This is a view of the 50H installed on Radio Caroline, a pirate station in the British Channel. more info is at www.rossrevenge.co.uk where the Ampliphase is discussed at length.
The 50H1 was "two-toned"
BTA-50J (1970)
The 50J was the last of the Ampliphase transmitters. Built starting in 1970. A solid state exciter was one of the upgrades. The IPA (two 4-250's) fed the pair of 4CX5000 drivers which drove the two 6697 PA tubes.
The 50J had no windows on the outside
	KFQD in Anchorage, AK had a BTA-50J in use until 2001

Thanks to Jack Sellmeyer and Nat Kayle, among others, for assistance in putting this page together.

This is the RCA Section of The Broadcast Archive

This is the RCA Section of
The Broadcast Archive