microphones

amplifiers

speakers

SPEAKER HOUSINGS � TRANSFORMERS

RE-ENTRANT HORNS AND DRIVERS

INTE~-COMMUNICATION UNITS � ACCESSORIES

STROMBERC-CARLSON COMPANY

Ideal for indoor use. The proper matching of the qualitycomponents used in assembling Economymaster Iassures peak performance at low cost. These budget-priced, hard-working units will combine to serve manypurposes with remarkable efficiency:

For outdoor application, you will find EconomymasterII an unbeatable matching of quality components in itsprice range. Its versatility and performance character-istics make this low cost, highly dependable ensembleworth many times the original cost. The Economymaster/I features:

Truly mobile outdoor equipment which will provideexcellent coverage over an extended area, The Mobil-master will serve innumerable purposes with un-matched efficiency. Its rugged durability, flexibility andperformance make the Mobilmaster outstanding in itsfield.

The Workmaster I is ideally suited for any number ofindoor applications. Featuring the perfect matching ofhighest quality components, the Workmaster I will giveyears of dependable, highly efficient service. True to itsname, it will prove the master of any task assigned to it.The Workmaster I includes:

� AU-62-B watt amplifier� Phono input jack� MR-34C-Controlled ReluctanceMicrophone� MS-26-Microphone Standwith On-Off Switch� RH-2B-D-Speaker Housing in Desert Sand� RC-27*-High-quality 8" Speaker*Four speakers may be employed without line-matchingtransformers; Up to twenty speakers withline-matching tra~sformers.

� AU-62-8 watt Amplifier� Phono Input Jack� MR-34C-Controlled ReluctanceMicrophone� MS-26-Microphone Standwith On-Off Switch� RS-14*-Weatherproof Re-EntrantLoudspeakerwith Built-in Driver Unit

*Four speakers may be employed without line-matchingtransformers; Up to twenty speakers withline-matching transformers.

� AM-48** -6 watt Amplifier. Operatesfrom 6volt storage battery. The AM-49 Amplifieroperatesfrom a 12 volt storage battery.

� MD-33C RuggedControlled ReluctanceMicrophone� Phono Input� RS-14*-12 watt, weatherproof OutdoorLoudspeakerwith Built-in Driver Unit

*Additional RS-14 Speakers may be used.**Speclfy 6 volt or 12 volt operation.

� AU-63-15 Watt Amplifier� PhonographInput� MR-34C-Controlled ReluctanceMicrophone� MS-26-Microphone Stand with Touch-to-TalkLockingSwitch

� RC-27*- Two High Quality 10Watt 8" Speakers� RH-28D- Two SpeakerHousingswith DesertSand Finish

*Will handle up to four RC-27 Speakers withoutLine-matching Transformers; up to 40 Speakerswith Line-matching Transformers.

microphones

Model M R-34CRELUCTANCE

Model M D-33CRELUCTANCE

A high level, highimpedance, controlledreluctance model forvoice paging, etc.

Rugged controlledreluctance model.Non-locking switchcloses separate line foroperati ng relays orsimilar application.

Model M D-43ALAVALIER

For chest, desk orhand use-indoors oroutdoors. Suppliedwith neck cord,supporl clips and 18"cord. Omnidirectionalpolar pattern. Either30-50 ohmimpedance.

The first link in the golden chain of quality communications equipment.There is a microphone for every purpose in this wide selection tohelp start your transmission on its merry way.

Model MD-28CSDYNAMIC

Multi-purposeclose-talking, highimpedance type. Canbe hung, hand-held,or mounted on stand.Equipped with slideswitch.

Model MD-36DYNAMIC

Model MD·37DYNAMIC

General purposemodel. Withstandshigh humidity,temperature extremes,mechanical shocks.Sliding contact switch.MD-36AS, lowimpedance. MD-36CShigh impedance.

Excellent for publicaddress and similaruses. Non-directionalpickup pattern at lowfrequencies becomesdirectionalwith increase infrequency. Slidingcontact switch.MD-37AS, lowimpedance. MD-37CS,high impedance.

Model Ms-41Model MD-22As Model MD-30 Model M D-38s Model MC-41 SHOULDER Model Ms-32A Model Ms-26DYNAMIC DYNAMIC DYNAMIC CARDIOID HOLDER DESK STAND DESK STAND

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I1iClose-talking, For finest installations. Uni-directional Provides free Adjustable model. Has touch-to-talk,

Can be used on dynamic type, movement of Heavy, non-tilt locking switch fornoise-cancelling, low Especially suited for stand, or suspended with sharper hands and body. base. relay operation orimpedance model for voice frequency overhead, or in hand. pickup pattern. Fine for microphone "on-off."high noise-level applications. Acoustical Multi-impedance demonstrators,areas. Ideal for Grip-to-talk stand treatment prevents switch allows lecturers.marine, railroad, with sliding clip to wind and breath working directlyfactory, power plant hold switch in "on" blasts. Sliding into low, mediumand similar position. MD-30A low contact switch. or high inputs.installations. impedance. MD-30C, Vertical tilt swivel.Press-to-talk switch. high impedance

3

WORKMASTER IIThe careful combining of just the right high-qualitycomponents assures you that the Workmaster II willmaster any of the many outdoor duties assigned to it.The quality construction of the components, the ruggeddependability and outstanding performance of theWorkmaster II make it an indispensable asset.

Designed for true Full Fidelity indoor performance, theBroadcaster offers superior audio reproduction in thefinest Stromberg-Carlson tradition. The careful match-ing of quality components gives the exact balance re-quired for Full Fidelity operation. The versatile Broad-caster includes:

Traditional Stromberg-Carlson quality, dependable,high-efficiency operation and functional versatility putthe Performer in a class by itself for outdoor use.Perfectly matched components to assure proper balanceguarantee the best performance possible. The powerfulPerformer features:

King of Kings is an apt description of the Power King.Virtually unlimited in its possible applications and withpower to spare, the Power King stands alone in its field.The careful selection of the right components assuresthe ultimate in power plus long life and efficient per-formance from the Power King, which includes:

� AU-63-PowerfuI15 Watt Amplifier� PhonographInput� MR-34C-Controlled ReluctanceMicrophone� MS-26- MicrophoneStand� RS-14*- Two 12Watt, WeatherproofRe-entrantloudspeakers with Built-in Driver Units

*Handles up to 4 Speakers without Line-matchingTransformers; up to 40 Speakers with Line-matchingTransformers.

� AU-64-Amplifier-30 Watts of PowerPlus!� PhonoInput� MC-41-Broadcast-type Cardioid Microphone.� MS-12-Microphone Floor Stand. Easilyadjusted� RF-473- Two 32Watt High Fidelity CoaxialDiffuser Speakers

� RH-62- Two SpeakerEnclosures

� AU-64-30 Watt Amplifier� PhonoInput� MD-30C-Dynamic Microphone� RP-34*-Four ruggedoutdoor Re-Entrant Horns� RD-24-Four driver units for RP-34 Horn*Handles up to 40 Horns using RD-21 Driver Units.

� AU-65-60 Watt Amplifier with Phone Input� MD-30C-Dynamic MicrophonewithGrip-to-Talk locking Switch

� RC-28-Four High Quality 8",12 Watt Speakers� TR-13-Four line-matching Transformers� RH-28D-Four SpeakerHousings� RP-27-Four Re-entrant Horns� RD-21- Four 30Watt Driver UnitsThe Power King will handle up to 100 speakers.

Model AU-35UNIVERSALAMPLIFIER50 watt output. Two 25-wattoutput channels, with sepa-rate volume controls. Threemicrophone and one phonoinput. Interconnecting jack.Treble and bass controls.

Model AU-62UNIVERSALAMPLIFIER8 Watt Output. One micro-phone and one phono Input.Treble control. Complete withTop Cover.

Top covers with 3-speed record players are available for the AU-64 (ModelPR-5) and AU-65 (Model PR-6).

AU-64 Model (PR-5) and AU-65 (Model PR-6)

Model MS-22 BANQUET STANDAdjustable 18" to 32" for table use; 8" base.

Model MS-12 FLOOR STANDAdjustable 34" to 64". Positive locking position. Heavy base.

Model MS-13 FLOOR STANDDeluxe model with automatic positive clutch. One hand operation. Nocreeping. Adjustable 34" to 64". 12" Base.

The careful selection of the right amplifier for the right job completes thesecond phase in the achievement of audio perfection. For dependability,quality and economy, "There is Nothing Finer Than a Stromberg-Carlson."

Model AU-36UNIVERSALAMPLIFIER50 watt output. One micro-phone and one phonographinput. Has "additional ampli-fier" jack. Treble and basscontrols.

MODEL PC-17PORTABLE CASEEquipped with 2 high quality8" speakers, 25 feet heavy-duty cable, and plugs wired toeach speaker. Takes any am-plifier not over 14" wide by 8"deep. Drilled to permit fas-tening AU-57 or AU-58 ampli-fier. Fabrikoid finish.

Model AU-65UNIVERSALAMPLIFIER60 Watts Output. Two Micro-phone and one Phono Input.Treble and Bass Controls.Top Cover with Self-Retrac-table Handles included.

Model AK-13 REMOTEVOLUME CONTROL

Provides individual control of vol-ume of each of four input sources.Supplied with connector plug. De-signed for use with Model AU-57amplifier which is equipped withremote volume control socket.

Model TM-8A PLUG-ININPUT TRANSFORMER

Designed for Model AU-57 ampli-fier, this plug-in unit provides meansof converting high impedance mi-crophone input to low impedance.

Model TM-10 )INPUT TRANSFORMER

Microphone line input transformerdesigned for easyconversion of highimpedance input to low impedance.

Model AU-57UNIVERSALAMPLIFIER25 watt output. Four micro-phone inputs, one with mag-netic crystal phono selectorswitch. Treble and bass con-trols. Provision for remotevolume control.

Model AU-63UNIVERSALAMPLIFIER16 Watts Output. One Micro-phone and one Phono Input.Treble Control. Ineludes TopCover with Self-RetractableHandles.

Model AV-38PRE-AMPLI FI ER

Multi-purpose line or voltageamplifier, ideal for remoteprogram pickup. Three low-impedance microphone andone high-impedance phonoinput. Treble control. Basscontrol on microphone. Bassboostcontrol on phono. Moni-tor headphone jack. Outputlevel meter. Built-in ACpowersupply.

complete re-entrant speakers

Models RS-5 and RS-6

Small re-entrant speakers, with built-in driverunits, for paging, etc. Ideal for loading platformsand exposed location. 6" bell, ai r column equivalentof 14". Input capacity: 3 watts RS-5,voice coil im-pedanceof 8 ohms; RS-6, 45 ohm impedance.

Model RS-14

Re-entrant, with built-in driver, handles up to12 watts of program material. Particularlyeffective in noisy locations. Suitable also foroutdoor installation. 9" bell, air column equiv-alent of 18". Voice coil impedance of 8 ohms.

Model AU-58UNIVERSALAMPLIFIER25 watt output. Two micro-phone inputs, one with mag-netic crystal phono selectorswitch. Treble control. Basscontrol.

Model AU-64UNIVERSALAMPLIFIER30 Watts Output. Two Micro-phones and one Phono Input.Treble Control. Ineludes TopCover with Self-RetractableHandles.

Models AM-48and AM-49MOBILEAMPLIFIERS6 watt output. One micro-phone and one phono input.Volume control. Model AM-48is for 6-volt storage batteryoperation. Model AM-49 oper-ates from 12-volt battery.

Model HS-101HEADPHONE SET

Famous Stromberg-Carlson telephonequality throughout. These headphonesare furnished complete with cord andare VA-approved. Plastic covered, ad-justable headband; nickel plated ex-posed parts. Permanent magnets ofAlnico metal. 2000 ohm DC resistance.

Model RF-460 HI-FI SPEAKERIdeal for smooth, wide-range reproduction forsmall-size enclosures and hard-to-fit locations. 8"cone with W' voice coil. 6.8 oz. Alnico V Magnet.Flux density 13,000gauss. 8 ohm impedance. Han-dles 12 watts of program material. Frequency re-sponse 45-14,000 cps. Moisture-resistant cone.

Model RC-61There are many applications for this 4" speaker.Handles 4 watts of program material. Voice coilimpedance of 3.2 ohms. Alnico V magnet, .82 oz.

Stromberg-Carlson's years of world leadership guarantee the very finest in sound-engineeredspeakers-an extremely vital element in optimum audio reproduction. "There is NothingFiner Than a Stromberg·Carlson" speaker for smooth frequency responseand top performance.

Model RF-473 HI-FICOAXIAL SPEAKERCombines high-power-handling capacity, wide tonalrange, smooth frequency response and exceptionaldurability. 12" curvilinear, moisture-resistant coneand coaxially located, exponentially shaped, high-frequency diffuser. Handles 32 watts of programmaterial. Better than 75 degrees angle of coverage.Frequency response: 30 to 14,000 cps. Back andfront dust covers protect against dust and otherforeign materials.

Model RC-59Powerful 6" x 9" oval cone speaker with voice coilimpedance of 3.2ohms. Has1.7oz. Alnico V magnet.Handles 7 watts of program material.

Model RH-29Two-way metalprojection housing for8" cone speaker.Brackets permitversatile mounting.Desert Sand finish.

Models RH-34and RH-54Ruggedly constructedtilt-type wall mountingcabinets in Desert Sandfinish. 7W angle tilt oneach side. RH-34 designedfor 8" speaker. RH-54designed for 12" speaker.Housings easily convertedto two-way use byaddition of RA-8 or RA-12back panel.

Models RA-8and RA-12Back panels withmatching finish andgrille cloth, permittingopen mounting. RA-8for RH-34 housing;RA-12 for RH-54cabinet.

Model RF-465 HI-FICOAXIAL SPEAKERTrue coaxial speaker system with "Omega M VoiceRing" horn loaded 2W' tweeter and separate 15"low-frequency woofer. Moisture-resistant cone. Fre-quency response: 30 to 20,000cps. Handles 35 wattsof program material. Better than 90 degrees angle ofcoverage. Engineered to match perfectly any type ofenclosure suitable for use with a 15" speaker.

Model RC-27A popular 8" cone speaker that handles 10 watts ofprogram material. Voice coil impedance: 8 ohms.Alnico V magnet. Flux density 8,500 gauss. Freq.response 55-13,000 cps.

Models RH-28and RH-28DAttractive plastic cabinetfor 5Y2" or 8" conespeakers. Model RH-28finished in Mottled Brown;RH-28D in Desert Sandenamel.

Model RH-62 )Larger size tilt -type woodcabinet for 12" speaker suchas RF-471. Directs sounddownward at 15° angle.Desert Sand finish.

Model RF-471 HI-FICOAXIAL SPEAKERFeatures exclusive carpinchoe-Ieather suspendedtweeter. 12" low frequency cone with 1'12" voicecoil, 20 oz. Alnico V magnet, flux density 11,000gauss; 2" high frequency unit with W' voice coil,aluminum spider, protective lens, 2.15 oz. Alnico Vmagnet, flux density 8,500gauss. 8 ohm impedance.Handles 32 watts of program material. Frequencyresponse 30-14,000 cps. Moisture-resistant cone.

Model RC-58This 12" permanent-magnet type cone sp'3aker hasvoice coil impedance of 8 ohms. Alnico V magnet.Flux density 8,500 gauss. Handles 16 watts of pro-gram material. Frequency response 55-13,000 cps.

Model RF-475 HI-FICOAXIAL SPEAKERA "power-plus" system with exceptionally heavymagnet. Finest reproduction at all volume levels.15" low frequency cone with 3" voice coil. 10'12lb.Alnico V magnet, flux density 11,500gauss; 5" highfrequency parametric horn with 10-element acous-tic lens, flux density 15,500gauss. 16 ohm imped-ance. Handles 40 watts of program material. Fre-quency response 30-16,500 cps. Moisture-resistantcone.

Model RC-62Dynamic 12" permanent -magnet type cone speakerwith frequency response of 50-13,500 cps. 6.8 oz.Alnico V Magnet. Flux density 13,000gauss. Voicecoil impedance: 8 ohms. Handles 20 Watts programmaterial.

Model RF-466 HI-FICOAXIAL SPEAKERPrecision engineered, budget priced coaxial speakerwith frequency response of 30-15,000 cps. Handles32 Watts of program material. More than 100 de-grees angle of coverage. 15" low frequency conewith 2" voice coil, 20 oz. Alnico V Magnet, flux den-sity 11,000gauss.23,4"high frequency unit with W'voice coil, 1.75 oz. Alnico V Magnet, flux density8,500 gauss. Voice coil impedance: 16 ohms. Mois-ture resistant cone. Magnet completely enclosed forfull protection.

Model RC-28High quality 8" Cone Speaker. Famous Alnico VMagnet. Handles 12 Watts of program material.Frequency response 50-13,500 cps. Voice coil im-pedance: 8 ohms, flux density 13,000gauss.

Models RH-35and RH-55Steel flush-mounting speakerbaffles, in Desert Sandcolor, for mounti ng onstandard Columbia box.Model RH-35 accommodates8" speaker, is 13" square.Model RH-55 is 19" squareand accommodates12" speaker.

Model RH-31AHandsome, triangular(corner) wood cabinet for 8"cone speaker. Desert Sandfinish.

Model RH-32For ceiling installations requiring3600 diffusion. Usewith 8"speaker. Satin aluminum finish.

Model RA-6Steel back box lined with plasticroughi ng campound-for 8"speaker. Equipped withplastic ring.Model RH-24

Steel ceiling grille, 10" diameter,with rubber gasket. Beigeenamel finish.

Models RP-27, RP-34, RP-44Ruggedly constructed. For use with Stromberg-Carlson driver units. Model RP-27 bell 15'12", aircolumn equivalent of 30", frequency cut-off 200cps.Model RP-34 bell 20", air column equivalent of 42",frequency cut-off 150 cps. Model RP-44 bell 25'12",air column equivalent of 53"; frequency cut-off120 cps.

Models RP-40, RP-503600 projectors for indoors and outdoors. UsewithStromberg-Carlson driver units. Model RP-40 bell24%", air column equivalent of 48", frequency cut-off 150 cps. Model RP-50 bell 281,4", air columnequivalent of 60", frequency cut-off 120 cps.

Model RD-21 DRIVER UNITInput capacity: 30 watts. Frequency range: 90-lD,OOO cps.Voicecoil: 16ohms. Built-in transformer.

Model RD-23 DRIVER UNITInput capacity: 25 watts. Frequency range: 90-lD,OOO cps. Voice coil: 16 ohms.

Model RP-48Dual re-entrant horn with twin air columns. Coverswide areas. Ideal for fixed or mobile mounting loca-tions. Mouth 91,4" x 18'12", depth lD1,4". Frequency'cut-off 250cps. Two driver units may be attached tosingle RP-48 by using RA-3 connector.

Model RD-24 DRIVER UNITInput capacity: 25 watts. frequency range: 90-6,000 cps. Voice coil: 16 ohms.

Model RA-3Two Driver UnitConnector

Model RA-2Mounting Bracket

inter-communication units

ModelTD-18Master StationDesk Phone

Stromberg-Carlson TelephoneInter-Communicating Systemsare available in selective ring-ing-common talking combina-tion; also in common ringing-common talking combinations.

Master Stations are the TO-18for desk use and the TW-28 forwall mounting. Sub-Stationsare the TD-ll for desk and theside-mounting TW-31, whichmay be mixed. The TO-ll canbe converted easily to wallmounting by means of a simpleConversion Kit (TK-3).

Model TW-31Sub-StationSide-MountingPhone

LINE-MATCHINGTRANSFORMERS

Good frequency response, minimum audio powerloss, a wide range of usable tap values and powerhandling capacities mark these line-matching trans-formers. Model TR-13 is rated at 2.5 watts, incorpo-rates a tapped secondary as well as three primarytap values. Model TR-20, power capacity of 12watts, offers four primary tap values. Model TR-30,rated at 12 watts, has five primary tap values forvoltage or impedance matching. Model TR-54, de-signed for outdoor use, has power capacity of 25watts and offers three secondary as well as fiveprimary tap values.

A DIVISION OF GENERAL DYNAMICS CORPORATION

1700 UNIVERSITY AVE. ROCHESTER 10, N. Y.

5.108 25M 556 GlP Printed in U.S.A.

MODEL AU-42 AMP-LIFIER

Economy must be considered for many soundequipment applications where dependability andperformance cannot be sacrificed. For this reason,Stromberg-Carlson builds a series of amplifierswith provision for one microphone and one phono-graph input. Thus, without sacrifice of quality,reduced cost is obtained.

Stromberg-Carlson Model AU-42 is the 1.5wattamplifier of this series. Circuit design permitsindependent regulation and mixing of the mi-crophone and phonograph or equivalent level in-puts. This makes possible such combinations asmicrophone program pickup with backgroundmusic supplied from a phonograph or wired-lineinput.

Although this amplifier provides for the simul-taneous use of only one microphone and onephonograph input, additional microphones can be

accommodated by connecting them to the ampli-fier one at a time. To accomplish this, the Strom-berg-Carlson No. 13 Type Key Box provides thebasis of an excellent switching device.

Push-pull beam-power tubes, multi-stage feed-back, careful circuit design and high-quality ma-terials, together with careful assembly and stricttesting make the Model AU-42 Amplifier an ex-cellent selection where audio power up to 15 wattsis adequate.

The Model AU-42 Amplifier is also available aspart of the Model PS-42 Portable System. Featur-ing a smartly-designed plywood case, neatly fin-ished in Glacier Gray fabricoid and using twoModel RC-24 eight-inch heavy-duty reproducers,this system should receive careful conside!,ationwhere versatility and portability are important

I

factors.

Model AU-42 Amplifier

Size with Cover: Width 13~", depth 7~", height10>i". Allow 1" front for knobs, 2" side andback for connectors.

Weight: Net 19Ibs., packed for shipment 22~ lbs.

Tubes Supplied: 1-6SF5, 1-6J5 or 6C5, 1-6SC7,2-6L6G,1-5Y3GTjG.

Power Supply: 105-125 volts, 50-60 cycles.

Power Consurned: 90 watts at 117 volts.

Inputs: One microphone, one phonograph, bothhigh impedance.

Controls: One microphone, one phonograph, onetreble attenuation control with combined on-offswitch. Treble control provides up to 18 db.attenuation at 10,000 c.p.s.

Power Gain: 108 db. from microphone input, 75db. from phonograph input, ratings based on50,000 ohm input source impedance.

Power Output: 15 watts with less than 5% totalharmonic content, measured at 400 c.p.s. witha supply voltage of 117 volts.

Output Tap Irnpedances: 4, 8, 15 and 500 ohms.

Other Useful Output Irnpedance Values: 350, 385,and 415 ohms. Obtained by connecting be-tween taps. (See Output Line Matching of thisdata sheet.)

Noise Level: 55 db. below rated output.

Frequency Response: 75 to 10,000 c.p.s. Variationless than +0 db. -3 db. from the 400 c.p.s.value.

Output Regulation: Approximately 3 db. variationfrom full load to no load.

Finish: Glacier Gray.

Underwriters' Listing: Listed under re-examinationservice by Underwriters' Laboratories, Inc.

In addition to the components shown on the schematic, it will be helpful to consult the following list ofparts that might be required to properly service this amplifier.

Part No.27958326433265739840

DescriptionFuse HolderExternal Microphone ConnectorSpeaker Line Connector "Knob

Part No.39844398474630646310

Tube Terminal

No. Tube Purpose 1 2 3 4 5 6 7 8-- -- -- -- -- -- --

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Second1 6J5 or Stage 0 *6.3 45 .. 0 · . *6.3 1.6

6C5 VoltageAmplifier

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Model AU-42 Amplifier

INPUTCONNECTIONS- A single-contact mIcro-phone connector is provided for the microphone.or other low-level, high-impedance input. Ascrew-type terminal strip is provided for a phono-graph or equivalent level high-impedance input.

OUTPUTCONNECTIONS-Two, parallel-connected,octal sockets on the rear of the amplifier baseprovide connection to the various taps of theoutput transformer.

CONTROLS-Independent microphone and phono-graph controls permit regulation of volume andmixing of the input signals. Any change in settingof one control has no effect on the operation ofthe others.The tone control, when rotated clockwise, de-

creases the response of the amplifier on the higheraudio frequencies. The A.C. off-on switch is com-bined with the tone control.

AMPLIFIER-Proper placement is important. Bylocating the amplifier close to the microphonelocation, wiring cost and noise pickup are re-duced; by locating it close to the reproducers,output power loss as well as wiring costs are re-duced. Equipment should be readily accessible tofacilitate proper maintenance. When mounting theamplifier in a cabinet or on a shelf, care must betaken to provide sufficient ventilation for adequatecooling. .

MICROPHONE-This amplifier is designed for usewith a Stromberg-Carlson high-impedance micro-phone. For best results the microphone cableshould not exceed fifty feet in length. When alonger microphone line (up to 5000 ft.) is re-quired, a Stromberg - Carlson low-impedancemicrophone may be used by employing a well-shielded input transformer at the amplifier input.Complete information and schematic diagram isgiven in the data sheet packed with each Strom"berg-Carlson microphone or see Sales Engineers'Manual, Section 6. Data sheets can be obtainedfrom your Stromberg-Carlson distributor.

REPRODUCERS-Locate the reproducers so that thespace between the reproducer and the area to becovered is clear of obstructions. Direct the re-producer so that sound is projected toward thecenter of the area to be covered.vVhen a reproducer and microphone must be

located in the same general area, they must beplaced so that a minimum of sound from the re-producer will re-enter the microphone. If sufficientsound, either direct or reflected from hard surfacesreturns to the microphone, acoustic feedback willresult. Acoustic feedback is caused by amplifiedsound being picked up by the microphone andfed back through the amplifier where it adds tothe original sound, building up until a continuouswhistle or howl is produced.

SYSTEMWIRING-Sound system wiring should beprotected against mechanical injury and moistureparticularly where it passes through walls or floors.Even a small amount of moisture may affect theinsulation of poorly protected wiring to such anextent as to impair the efficiency of the system.

MICROPHONELINES-Keep microphone lines atleast six inches away from other electric circuitsincluding amplifier output lines. If it is necessaryto run microphone lines parallel to other electriccircuits, keep at least two feet separation.vVhen enclosed in conduit, microphone lines

may be run together but never run any othertype of wiring in the same conduit.If the shield on the microphone line is used as

the return conductor, it must be in·sulated through-out its length from contact with conduits, etc.,and grounded only at the amplifier where thegroilnd is supplied by the amplifier, through themicrophone chassis connector.If a shielded-twisted pair is used for a micro-

phone line, it is preferable to insulate the shieldfrom contact with conduits, etc., although it maynot be necessary on short runs.

AMPLIFIERGROUND-A good building ground,such as a connection from a cold water pipe or

Model AU-42 Amplifier

the frame of a steel building, should be terminatedunder the knurled nut located on the rear of tl~eamplifier.

REPRODUCER LiNES-When supplied as the ModelPS-42 Portable, two speakers each with 25 feetof cable and plug are provid~d correctly-wiredfor insertion in the output sockets of the ampli-fier. One speaker case has a socket imtalled, intowhich the s}:eaker cord plug of the second speakercan be inserted for cascade connection.'~7hen reproducers are to be located at a distance

from the amplifier, care must be taken to see thatline loss is not excessive. Line loss can be reducedby increasing the size of the wire or by usingtransformers at each reproducer location to raisethe impedance of the line. Additional informationis given in Sales Engineers' Manual, Section 24,wllich may be obtained from your Stromberg-Carlson distributor.

OUTPUT LINE MATCHING-The following chartlists the amplifier output taps provided to ac-commodate various reproducer loads. The audiovoltage present when the amplifier IS deliveringrated output, is also listed:

Terminal8-18-28-37-37-27-18-7

Output(at 15 watts)8 volts11 volts15 volts7'2 volts76 volts79 volts87 volts

Irnpedance4 ohms8 ohms16 ohms350 ohmsS85 ohms415 ohms500 ohms

To determine the power into any reproducer,divide the impedance of the amplifier output tapby the impedance of the reproducer to be used(or the tap on the reproducer transformer). Thisis the fraction of the total power output of theamplifier delivered to that reproducer. For ex-ample, if a '2,500 ohm reproducer is connected toa 500 ohm output tap, that reproducer will drawone-fifth of the power delivered by the amplifier.Thus, by proper selection of loudspeaker impe-dance, different amounts of power can be deliveredto a number of speakers, all connected in parallelto the same amplifier. The rule applies equallywell whether the reproducers are all connected to

the same output tap, or if connected to severaldifferent-impedance taps. The sum of all thesefractions of total amplifier output power shouldbe equal to one for the best matching. If theimpedances of available taps do not permit perfe<.'tmatching, the sum should be less than one.

Adjust the volume controls to gIve the desir"edamplifier output. A successful installation permitseveryone to hear comfortably. Loudness is notnecessarily essential. To keep hum and noise at aIJ;linimum, itis important that any volume controlbe set at zero when that input is not being used.If after precautions mentioned under "Location

of Equipment" have been observed and acousticalfeedback is still encountered, the following shouldbe tried:

1. Relocate the reproducers and/or microphone inrelation to each other.

'2. Reduce frequency response of amplifier by ad-justment of treble control.

S. Reduce setting of microphone volume control.

4. Speak closer to the microphone to obtain in-creased volume.

The amplifier can readily be adapted to theprogram being reproduced or to the acoustics ofthe room by means of the tone control.

Treble attenuation largely eliminate's the effectof needle scratch when recordings are used and isuseful on microphone reproduction in reducingshrillness and acoustical feedback.

SERVICEFUSE REPLACEMENT - When replacing a blownfuse use only a '2 amp. 250 volt, type SAG. Touse a fuse of higher rating will needlessly en-danger the windings of the power transformer.

MAINTENANCE-The values and part number ofthe various components are given in the list ofparts on the schematic diagram. The voltagespresent at the various socket terminals of a nor-mal operating amplifier are given in the voltagechart. Always use Stromberg-Carlson replacementparts for Straight-Line Communication equipmentperformance.

ModeJ AU-42 Amplifier

the frame of a steel building, should be terminatedunder the knurled nut located on the rear of tileamplifier.

REPRODUCER LINES-When supplied as the ModelPS-42 Portable, two speakers each with 25 feetof cable and plug are provid~d correctly-wiredfor insertion in the output sockets of the ampli-fier. One speaker .case has a socket installed, intowhich the sreaker cord plug of the second speakcrcan be inserted for cascade connection."Vhen reproducers are to be located at a distance

from the amplifier, care must be taken to see thatline loss is not excessive. Line loss can be reducedby increasing the size of the wire or by usingtransformers at each reproducer location to raisethe impedance of the line. Additional informationis given in Sales Engineers' Manual, Section 24,which may be obtained from your Stromberg-Carlson distributor.

OUTPUT LINE MATCHING-The following chartlists the amplifier output taps provided to ac-commodate various reproducer loads. The audiovoltage present when the amplifier IS deliveringrated output, is also listed:

Terminal8-18-28-37-37-27-18-7

Output(at 15 watts)8 volts11 volts15 volts72 volts76 volts79 volts87 volts

Impedance4 ohms8 ohms16 ohms350 ohms385 ohms415 ohms500 ohms

To determine the power into any reproducer,divide the impedance of the amplifier output tapby the impedance of the reproducer to be used(or the tap on the reproducer transformer). Thisis the fraction of the total power output of theamplifier delivered to that reproducer. For ex-ample, if a 2,500 ohm reproducer is connected toa 500 ohm output tap, that reproducer will drawone-fifth of the power delivered by the amplifier.Thus, by proper selection of loudspeaker impe-dance, different amounts of power can be deliveredto a number of speakers, all connected in parallelto the same amplifier. The rule applies equallywell whether the reproducers are all connected to

the same output tap, or if connected to severaldifferent-impedance taps. The sum of all thesefractions of total amplifier output power shouldbe equal to one for the best matching, If theimpedances of available taps do not permit perfe('tmatching, the sum should be less than one.

Adjust the volume controls to gIve the desiredamplifier output. A successful installation permitseveryone to hear comfortably. Loudness is notnecessarily essential. To keep hum and noise at an;Iinimum, it is "important that any volume controlbe set at zero when that input is not being used.If after precautions mentioned under "Location

of Equipment" have been observed and acousticalfeedback is still encountered, the following shouldbe tried:

1. Relocate the reproducers and/or micl'Ophone inrelation to each other.

2. Reduce frequency response of amplifier by ad-justment of treble control.

3. Reduce setting of microphone volume control.

4. Speak closer to the microphone to obtain in-creased volume.

The amplifier can readily be adapted to theprogram being reproduced or to the acoustics ofthe room by means of the tone control.

Treble attenuation largely eliminate's the effedof needle scratch when recordings are used and isuseful on microphone reproduction III reducingshrillness and acoustical feedback.

FUSE REPLACEMENT - When replacing a blownfuse use only a 2 amp. 250 volt, type 3AG. Touse a fuse of higher rating will needlessly en-danger the windings of the power transformer.

MAINTENANCE-The values and part number ofthe various components are given in the list ofparts on the schematic diagram. The voltagespresent at the various socket terminals of a nor-mal operating amplifier are given in the voltagechart. Always use Stromberg-Carlson replacementparts for Straight-Line Communication equipmentperformance.

Model AU-42 Amplifier

Licensed under U. S. patents of American Telephone and Telegraph Company and Western Electric Company,Incorporated, for use only in public address systems. phonograph distribution systems, systems for distributionfrmn radio broadcast receiving sets or musical instruments or of programs received over wires, and in speech

input systems and monitoring systems for radiotelephone broadcasting stations.

BRANCHES

564-70 WEST ADAMS STREET, CHICAGO 6, ILLINOIS 0, 2017 GRAND AVENUE, KANSAS CITY, MISSOURI

325 NINTH STREET, SAN FRANCISCO 3, CALIF.