here is what you want in your 250 watt

AM TRANSMITTER

Raytheon MANUFACTURING COMPANY

Simplified ... More Reliable

RAYTHEON'S new RA -250 is a precision engi- neered, completely modern broadcast transmitter which incorporates many important improve- ments in a simplified circuit design.

Better program quality is achieved by specially designed audio transformers and triode type tubes having an inherently lower distortion level. The noise level is over 60 db below 100% modulation and the frequency response is flat between 30 and 10,000 cycles per second.

Simplified circuits, highest quality components which operate at well below their capacity, and triode type tubes give a more positive guarantee than ever before against program interruption. Even a feed-back failure does not put this trans- mitter off the air.

All controls are centralized on the front panel; all circuits are completely metered and instantly tested. It is necessary to tune only two stages, the RF drive amplifier and the power amplifier. Low speed motor tuning gives a positive microm- eter adjustment of these stages.

Maintenance functions are made easy. Vertical type chassis, full length double rear doors and hinged full length side panels give instant acces- sibility to all wiring and component parts. Every part is directly accessible without having to first remove several others. Safety interlocks and a

dead front panel protect operating personnel at all times.

Our broadcast engineers, experienced in the en- gineering and programing requirements of the modern broadcast station, have, we believe, achieved all the qualities most desired in an AM transmitter. You will note, too, that no quality has suffered for the good of another.

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an Important Improvements

Simplified, More Efficient Circuits-A high level modulation system eliminates the necessity of complicated and critical adjustment of linear amplifiers and re-

duces harmonic distortion to a minimum. Low tube cost and considerably lower power consumption are added advantages of this system.

Increased Operating Efficiency-The use of most modern improved compo- nents which are operated as well below their maximum capacity together with simplified circuit design greatly increases overall operating efficiency.

Greater Dependability-Due to the use of Triode type tubes, feedback failure will not cause a complete breakdown and the signal quality will still be good. Feedback is actually unnecessary, in this simplified circuit, to put a signal on the air but its inclusion further improves the quality of the signal.

Simple, Speedy and Accurate Tuning-All operational controls are centralized on the front panel; it is not necessary to make any adjustments inside the trans- mitter. Every circuit is completely metered and instantly checked. Only two stages are tuned, the RF drive amplifier and the power amplifier. A clutch equipped low speed motor makes micrometer adjustment of these stages very simple.

Silent Operation-Natural air cooling means complete freedom from blower noise, permitting the use of microphones in the same room with the transmitter. This silent operation is especially appreciated by stations planning to locate their trans- mitter in their studio, or where it is advantageous in early or late programs to have the transmitter operator double as an announcer at the transmitting station.

Low Audio Distortion-Triode type tubes used in the audio stages of this trans- mitter have an inherently lower distortion level. Specially designed audio trans- formers reduce the audio distortion still further.

Low Noise Level- The noise level of the RA -250 far exceeds the minimum F.C.C. requirement. It is actually better than minus 60 db below 100% modulation.

Easy Servicing- Symmetrical mechanical layout and complete accessibility through double rear doors and hinged side panels make the RA -250 a favorite with broad- cast engineers. Any component may be replaced and wiring checked with a mini- mum of time and effort. Full length hinged side panels swing open to expose all chassis cabling; double rear doors open the full height of the chassis.

Quiet, Natural Air Cooling- The RA -250 is so designed that natural ventilation adequately cools the transmitter at all times. Vertical chassis construction plus door and ceiling louvres allow free circulation of convective air currents. All dan- ger of fire or other damage due to a blower failure is eliminated.

Easily Meets All F.C.C. Requirements-All electrical characteristics easily meet all requirements of the F.C.C. Each transmitter is completely performance tested and tuned to the correct operating frequency before it is shipped. All con-

nections necessary for installation are clearly indicated and easy to make.

STRAIGHTFORWARD simplicity of design is readily a parent from the above schematic.

The RF circuit shows the 6J5 crystal oscillator with two crystal sockets either of which may be connected from a front panel switch. The plate circuit of the oscillator is made broad -band to eliminate tuning and reaction on the crystal frequency. The 807 buffer is operated as a class A stage with broad -band untuned plate circuit which insures complete isolation of the oscillator stage. An 813 operating well below maximum ratings drives the push-pull 810 final amplifier with a large reserve of driving power.

Use of the push-pull arrangement in the power amplifier reduces harmonic output and simplifies neutralization. The adjustable output coil in the final tank circuit is designed to feed standard type transmission lines from 70 to 250 ohms impedance.

The audio system is of the class B type for high level modulation. Push-pull circuits are used throughout with 2-6J5 tubes in the first stage, 4-6B4 tubes are used as audio drivers and 2-810 tubes as modulators. Specially designed driver and modulation transformers permit proper use of feed-back networks. The phase shift in the modulation transformer has been reduced to the point where effective feed- back is possible over the entire audio range of the transmitter. Distortion and noise are thus held to a minimum. Separate bias controls permit matching of modulator tubes for best operation.

The main power supply has been designed to pro- vide ample margin for all percentages of modulation with excellent regulation. A separate bias supply is provided with interlock relay for the protection of the high power tubes.

Control, interlock and power starting circuits are designed for protection of the equipment and oper- ating personnel as well as ease of operation and maintenance.

All component parts have been chosen to provide a good safety factor for long continued operation with- out failure.

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iagram o' ayt eon s2 5 Watt AM Transmitter-RA-250

MODERN VERTICAL CHASSIS

CONSTRUCTION

THIS FULL LENGTH interior view shows the clean, modern vertical type of construction used in this transmitter. This type construction gives complete accessibility to all component parts, greatly simplify- ing maintenance and servicing. Circuit symmetry and highest efficiency have been achieved in the layout of all parts. Complicated gear or flexible shaft drive for tuning have been replaced with modern motor drive. Grouping of all controls on a single recessed panel located for convenience and operating ease is thus readily accomplished.

Using two full length doors, in place of one as com- monly used, allows the transmitter to be placed much closer to a wall or partition without sacrificing accessi- bility. High voltage interlocks are, of course, provided on each door. A locking type door handle prevents unauthorized entry into the cabinet.

Placement of parts is evident from the picture. The large power and audio components are placed on a heavy sheet at the bottom of the cabinet. Facing the rear, the right hand wall carries all of the control relays and contractors. The front wall carries the radio frequency circuits starting with the oscillator and buffer chassis immediately above the power units fol- lowed by the 813 driver stage and the 810 output stage. The left wall carries several small chassis for rectifier tubes, bias supply, audio amplifier and modulation stages and low voltage power supply.

Openings are provided through the base and in the rear for conduit and wiring entrances. If coaxial line is used this may be brought in either overhead or through the base. An open wire line connection is furnished in the top only.

ter

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1. Symmetrical Layout Increases Efficiency

This view shows. ii more detail, the RF output stage and the modulator chassis. Cleaniess accessibility and symmet ical layou- are immediately evident

2. Transformers and Buffer Chassis

The crystal Dsci;lator and the buffer chassis is located immediately above the power Lnits. This location keeps the unit away tircrr heat generated by the -ectifer and sigh power tubes.

c5leezt

i

250 Watt AM Transmitter-RA-250 ELECTRICAL CHARACTERISTICS: Nominal Carrier Output 250 Watts Frequency Range 530 KC to 1600 KC Power Supply 208/230 volts, 3 wire, single phase, 50-60 Cycles Power Consumption 1703 Watts Radio Frequency Stability ±10 Cycles Modulation 100% High Level Audio Input (500/600 ohm source) for 100% Modulation .0 db

(1 Milliwatt Reference Level) A erage Program Level -5 db (1 Milliwatt Reference Level) Audio Frequency Response ±1 db from 30-10,000 Cycles Audio Distortion (50-7500 Cycles) 2.0% or less with 95°o Modulation

1.8°'o or less with 85% Modulation Noise Level 60 db below 100% Modulation

TUBE COMPLEMENT: Oscillator 6J5 Buffer .... 807

813 2 810's Push -Pull

Audio Amplifier 2 6J5's Push PullTriodes Audio Driver 4 6B4G Push -Pull Parallel Triodes Audio Modulator 2 810's Push -Pull Class B

R -F Low Voltage Power Supply Rectifier 350 Volt 200 ma I-5U4G

R -F Driver R -F Final

Modulator Low Voltage Power Supply Rectifier Modulator Bias Power Supply Rectifier High Voltage Power Supply Rectifier

MECHANICAL SPECIFICATIONS: Weight

350 Volt 200 ma 1-5Ú4G 35 Volt 240 ma 1-5U4G

1500 Volt 700 ma 2-872a's

Sise 1200 Lbs.

32'/s" Wide; 29" Deep; 80" High

FCC FILING DATA jimingli Applicants intending to use the Raytheon RA -250 Transmitter, in applying for a coAstruction permit, are required to fill in the following technical information on pages 28, 29 and 30 of FCC Form No. 301.

(a)

(b) (d)

(e) (h) (i) (i)

(a)

(b) (c)

Paragraph 18 should

Raytheon Manufacturing Company Type RA -250

(c) On file On file (except for last paragraph where

"not applicable" should be inserted) (f), (g) On file Not applicable On file Should be filled in by applicant

Paragraph 19 should

Raytheon Manufacturing Company part of Type RA -250

On file First line insert "Manufacturer", Second

be filled in as follows:

(k) Should be filled in by applicant (1) Plate voltage meter, on file. Serial number

should be supplied by applicant on in- stallation of transmitter. Plate ammeter- same as plate voltage meter. Antenna ammeter-same as plate voltage meter.

(m) On file (n) 300 watts (o) 250 watts

be filled in as follows:

and Third lines-Applicant must insert frequency in kilocycles at 60° centigrade.

(d) (e), (f), (g), (h), (i), (J), (k), (1), (m) On file

IN ORDER TO CONSTANTLY INCORPORATE THE FINEST IN ENGI- NEERING, DESIGN AND COMPONENTS IN OUR BROADCAST EQUIPMENT RAYTHEON RESERVES THE RIGHT TO MAKE ENGINEERING CHANGES

&cei.>ince in etem.cc.s

PRINTED IN U.'i.A. DL -R-407.746

RAYTHEON MANUFACTURING COMPANY Broadcast Equipment Division

7517 NORTH CLARK STREET, CHICAGO 26. ILLINOIS