RCA ET-4750

GENERAL DESCRIPTION

"RADIO CARACAS" - ONE OF VENEZUELA'S FINEST

photo RCA ET-4750

Pioneer station installs latest-type RCA equipment for greater public service

CARACAS, capital of Venezuela, has many fine, RCA-equipped broadcasting stations built to exacting Ministry of Communications regulations. The Ministry is patterned after our own F.C.C. The pioneer among them has been Radio Caracas. The present owners of this station, then as now, were agents for the entire country for RCA Victor, and in December, 1930 a small 100 watt transmitter was inaugurated to fulfill the need for a well-organized commercial broadcast service. Sales of RCA Victor radios and improvements to the station increased apace. Two years later a 5-KW equipment, the old RCA Model 5-A long wave transmitter was inaugurated as YV1BC on a frequency of 960 kc., on which channel it has continued to this day.

This power increase, together with the addition of a complementary transmitter in the 49 meter band, brought more receiver sales, better programs and revenues, and, like all other successful ventures, competition.

Greater Coverage Required

After some years of service and an increasing number of stations being established in Caracas, the need became apparent for greater coverage of the interior of the vast country, while retaining a strong primary service area in the capital and the surrounding Federal District. Experiments on short wave had meanwhile indicated the advantage of the 62 meter band over 49 meters for continuous day and night coverage of a 400 mile East-West radius, thereby avoiding the interference and crowded condition of 49 meters and minimizing fading effects. Actually, at this time both the Republics of Colombia and Venezuela were pioneering 62 meter operation.

The 5-A long wave equipment was, therefore, reconstructed for 62 meter operation and an RCA 1-G, 1000 watt transmitter was purchased for use on 960 kc for local coverage. At this time two completely new air-conditioned, acoustically-treated studios, a welcome innovation in that part of the world, were inaugurated, 100% RCA -equipped.

Clear Channel

In 1939 a regional frequency convention for the 62 meter band was held in Bogota between Venezuela, Colombia, Brazil, Ecuador and Peru at which time the present 4920 kc. wave was assigned as a clear channel for Radio Caracas with a power of 5000 watts. Continuing their policy of keeping abreast or ahead of all other stations in their territory and to fully utilize their new channel, Radio Caracas requested the RCA Manufacturing Company, Inc. to submit the design of a high frequency transmitter.

Prime requisites for the new transmitter were for minimum operation and service costs with simplicity of installation and the provision for covering all short wave channels down to the 13 meter band in case of possible future changes of frequency assignments. Also the elimination of water-cooling equipment was desired.

At this time RCA was completing their latest Model ET-4750 high frequency broadcast transmitter designed for just such requirements for government and commercial stations throughout the world. This equipment which is now available for general sale, includes many new features giving high fidelity operation with a remarkable low cost.

Use of the new RCA-889R air-cooled triodes in the final stage of this transmitter gives an antenna output of 7½ kilowatts carrier power down to the highest frequencies at which this equipment is designed to operate.

Since the ET-4750 transmitter is likely to be of general interest, technically, to our readers it may be mentioned that an exceeding simple yet effective tube line-up is used. In the radio frequency portion an 807 crystal oscillator is followed by an 807 buffer/doubler stage, an intermediate power amplifier stage of four 813 beam-power pentodes driving the two air-cooled RCA-889R's which constitute the final Class C modulated-amplifier. These tubes are modulated in turn by two air-cooled RCA-891R's in Class B, driven by four RCA-845's, two RCA-807's and two RCA-1603's in turn. The use of straight Class B audio is made by reasons of simplicity of operation and to obtain best possible audio qualty. Inverse feed-back over the audio portion of the transmitter by means of a resistance filter loop further aids this purpose with the result that residual noise and ripple components of the carrier are 50 db. or better below 100% modulation while the audio frequency characteristic does not vary beyond 1.5 db. from 30 cycles to beyond 7500 cycles.

Vertical Construction

Mechanically the transmitter is composed of four main panels mounted vertically in back of a unified front. On the front panel are located meters, controls, and indicator lights necessary for the proper operation of the equipment. The left vertical panel includes the control circuit parts; the next panel includes the low power radio frequency and the high power output tubes; the fourth panel includes the radio frequency output plate and transmission line coupling circuits. The rectifiers and their associated equipments are located in a separate angle frame constructed unit. The plate transformers for the 6000 and 4000 volt rectifiers are separate units. The modulation transformer, reactor, and associated parts are mounted on a separate sub base. The complete equipment requires floor space of approximately 11 feet wide by 10 feet deep. The height over the frames is 72⅞ inches. The total equipment weighs approximately 9000 pounds.

Radio Caracas is operated by C. A. Almacen Americano, owned by Mr. W. H. Phelps, Jr., this organization being one of the oldest and best-known importing houses in Venezuela, handling the entire RCA line from RCA Victor home receivers to the largest sized RCA Transoceanic Communications equipment for the Venezuelan Government Radiotelegraph Service. Almacen Americano have branch stores located in all cities of importance through-out the Republic and in addition to handling RCA Victor, also represent many other well-known American lines. This prominent house is an important link in the chain of increasing goodwill and closer commercial relations between the two Americas.

Program service has gradually increased throughout the years at Radio Caracas and now under the direction of Mr. Ricardo Espina, the well-known manager. Program time amounts to 18 hourscontinuous daily entertainment. Of all the Latin American stations in this region, Radio Caracas is probably the most noted for the number of radio celebrities appearing on its programs. Cuba, Mexico and other countries send their stars regularly for Caracas engagements.

TUBE COMPLEMENT
RF stages		AF stages and modulator		Rectifiers
Number	Type	Number	Type	Number	Type
2	889-R	2	891-R
2	813	4	845
2	807	2	807
		2	1603

THIS TYPE OF TRANSMITTER IS INSTALLED IN THE FOLLOWING COUNTRIES
	ITU	Country	ITU	Country
	AUS	AUSTRALIA	COD	CONGO DEMOCRATIC REPUBLIC
	LBY	LIBYA	MOZ	MOZAMBIQUE
	VEN	VENEZUELA