Stromberg Carlson 734, 744, 635, 636, 638, 641, 642, 645, 846, 10
Contents
1. 100 000 Brown Black Yellow R3 Grid Bias of Feeder of First I 100 000 Brown Black Yellow R4 Filter Resistor Screen Circuits of SG 600 Blue Black Brown R5 Filter Resistor Plate Circuits of SG 600 Blue Black Brown R6 Cathode Res of R F Ampl and 1st I F Ampl Tubes 450 Wire Wound R7 Cathode Resistor Second I 600 Blue Black Brown R8 Filter Resistor Plate Circuit 2nd I 10 000 Brown Black Orange R9 Demodulator Grid 250 000 Red Green Yellow R10 Demodulator Grid Circuit Filter 100 000 Brown Black Yellow Plate Resistor of 1 megohm Brown Black Green R12 Filter Resistor Plate Circuit of Demodulator 500 000 Green Black Yellow R13 Filter Resistor Plate Circuit of 100 000 Brown Black Yellow R14 Volume Control 500 000 R15 Hum Adjuster 400 Wire Wound R16 Biasing Resistor of Power Output 750 Wire Wound R17 Midtap Resistor Filament Circuit of Output Tubes 10 Wire Wound R18 Series Grid Resistor of2. 500 Green Black Brown R19 Cathode Resistor of Mixer 6 500 Blue Green Red R20 Cathode Resistor of 6 500 Blue Green Red R21 Section of Voltage Divider 1 575 Wire Wound R22 Section of Voltage Divider 1 220 Wrie Wound R23 Section of Voltage Divider Resistor 144 Wire Wound R24 Section of Voltage Divider 520 Wire Wound R25 Section of Voltage Divider 285 Wire Wound R26 Midtap Resistor Heater Circuit at Ist I Tube Ju 3 Wire Wound Stromberg Carlson 29 REVISL PER DOTTED LINES amp RES VALUES PICKUP SWITCH FOR 257 ANT t RF AMP MIXER DEM gomu AUDIO OUTPUT TUBES AUDIO e INPUT TRANSE E AUDIO OUTPUT SHORT o SPEAKER CONNECTOR m 000000 000009 00009 0 000000 B 1 00000054 pa GE Xena E gt pe 000000 000000 gt 000000 au E S SE CHASSIS 8 8 3 Re ins SR SRT A OS Dl DEI INA Ry ELECTRO DYNAMIC LOUD SPEAKER 1 1
3. ze 29 T3 POWER OUTLET 5 gt RECEPTACLE D Y 23 5 gt 2 55 3 AC POWER Stromberg Carlson 30 Fig 17 Stromberg Carlson Models 25 and 26 Fig 17 shows the complete circuit connections for the Chassis receivers Of course there may be some variations but in used in models 25 and 26 general the values should be within the limits given on the table Table No 10 gives the correct operating voltage for these TABLE No 10 Type Position A Volts B Volts C Volts Screen Grid Volts 24 Radio Frequency 2 4 135 150 235 130 150 24 Ist Detector 2 4 135 150 2 5 130 150 27 Oscillator 2 4 80 90 13 24 2 4 135 150 2 5 130 150 24 2nd Detector 2 4 190 215 7 130 150 45 Audio 2 4 225 255 40 50 45 Audio 2 4 225 255 40 50 80 Rectifier 4 8 320 350 Stromberg Carlson 31
4. 60 000 Blue Black Orange R13 Section of Voltage Divider 1 575 Wire Wound R14 Section of Voltage Divider amp 900 Wire Wound R15 Volume Control 1 000 Wire Wound R16 Section of Voltage Divider amp 60 Wire Wound R17 Cathode Resistor of 30 000 Orange Black Orange R18 Hum Adjuster 400 Wire Wound R19 Variable Resistor of Automatic Clarifier Circuit 100 000 Carbon Potentiometer Stromberg Carlson 26 Stromberg Carlson Model 22 The model 22 like the models 19 and 20 is a superheterodyne A complete circuit diagram is shown in Fig No 16 On the dia The tubes in it are quite similar to those employed in the 19 grams the values of all fixed condensers and resistors are in and 20 models except that one additional audio frequency tube dicated while table No 9 gives the correct operating voltages is employed and the receiver is designed with automatic vol for the various tubes ume control TABLE No 9 Type Position A Volts B Volts C Volts Screen Grid Volts 35 Radio Frequency 2 4 135 155 4 75 90 35 lst Detector 2 4 135 155 9 4 75 90 27 Oscillator 2 4 75 90 18 5 21 0 35 Ist I 2 4 135 155 4 1 75
5. 7 000000 eee 22 2 195 527 8 gt DIAL LAMP MILO SWITCH 000000 50h Ux 250 OR Fig 3 Stromberg Carison 4 While the 200 detector is more sensitive than the 201 A sometimes the increased noise due to the greater sensitivity of the tube may be objectionable especially if the owner of the receiver is not particularly interested in the reception of distant stations In such cases it is best to use a 201 A or 301 A tube as a detector Stromberg Carlson Model 744 In the model 744 there are four stages of tuned radio fre quency amplification detector and two stages of audio ampli fication The connections are very similar to the model 734 as will be seen by comparing Fig 2 with Fig 1 However in the model 744 an untuned antenna coupling stage is not used and it is designed only for use with a loop antenna In the model 744 as in the 734 the filaments of all tubes except the power tubes are connected in series and are supplied with direct cur rent The power tube filament is supplied with 734 volts alter nating current from a low voltage secondary winding on the power transformer with which the set is equipped Models 635 and 636 Receivers Three stages of tuned radio frequency amplification detector and two stages of audio frequency amplification are employed in both of these receivers All tubes are of the type 27 heater type except the audio output tube wh
6. A double volume control is used this control being operated from a single knob One section of the volume control consists of a 2000 ohm potentiometer and varies the input from the an tenna to the first RF transformer and the other a potentiometer which varies the grid bias on the first two RF tubes A power detector is used and operates with a plate potential of approximately 30 volts and a bias of 9 volts the bias voltage being supplied by a 9 volt C battery The first two stages of audio amplification are resistance coupled and the third stage which is connected in push pull 1s designed to supply a dynamic speaker with a voice coil of 13 ohms impedance CHASSIS BASE 20000 0000000 D C POWER SUPPLY UNE FILTER ON OFF SWITCH 00025 MF D 00025 7 7 5 dul 000 M 0000000 5 9 Si PICK UP C PICK UP JACK 2ND RF Ista 2 001 MF 20080 00 v 166 Le __ _ COROS RECEPTACLE RESISTOR UNIT IN CHASSIS SPEAKER FIELO Fig 11 Stromberg Carlson 17 Since the 45 tube filaments require only 114 amperes of current while all other tubes require 1 75 amperes a Mazda No 31 pilot lamp is shunted across the filaments of the 45 tubes If the receiver is operated with
7. 45 In this receiver as in several other Stromberg Carlson models a double volume control is used A 20 000 ohm potentiometer is connected across the primary of the antenna coil with its variable point connected to ground other part of the volume con trol varies the C bias on the grids of the first and second R F tubes through an 800 ohm potentiometer A diagram of the circuit is shown in Fig 7 The capacity of all fixed condensers and the values of all resistors are shown on the diagram as an aid in making further tests The power transformer has four secondary windings the first of which supples about 2 4 volts for the heaters of the R tubes and the detector The second supplies about 2 4 volts for the filament of the 45 tube The third winding supplies high voltage to the rectifier where it is changed to direct current for the plate supply and grid bias voltages The fourth winding supplies about 4 7 volts for the filament of the 80 full wave rectifier Since 24 screen grid tubes are used in the R F stages no meaus of neutralizing is required Each of the tuning condensers is provided with a small trimmer These trimming condensers are used to balance or equalize the capacity of the main tuning condensers to allow perfect one dial tuning The correct plate voltage for the R F tubes is about 140 volts for the detector about 250 volts and for the power tubes about 250 volts The correct grid biases are as follows
8. 90 35 2nd I 2 4 220 245 2 8 75 90 27 2nd Detector 2 4 35 40 27 15 Audio 2 4 135 155 11 6 45 2nd Audio 2 4 230 26 45 55 45 2nd Audio 2 4 230 260 45 55 80 Rectifier 4 8 325 355 Stromberg Carlson 27 3 PICK UP Samy SWITCH PICK UP JACK ANT 1st AUDIO AUDIO OUTPUT AUDIO OUTPUT 9 AMPLIFIER MIXER TUBE dst F AMPLIFIER 2nd 1 F AMPLIFIER TUBE TUBES TRANS r SILENT KEY INPUT 113 TRANS 8 a la SPEAKER CONNECTOR 5 5 3 ES F OR 60 a mma GNO BW LZ 21 8 1 Lol Load IIl TIT E ELECTRODYNAMIC LOUD SPEAKER POWER SER OUTLET s 83 54 RECEPTACLE 2 2 4 AAA POWER pum Fig 16 Stromberg Carlson 28 In case it is necessary to adjust or align one of these receivers The following table gives the values of a l fixed resistors to a broadcast oscillator and output meter are necessary together gether with the color coding as an aid in identifying by color with a 175 kilocycle oscillator for adjusting the intermediate when making service tests frequency transformer COLOR CODING Designation FUNCTIONS Value Ohms BODY TIP DOT Rl Grid Bias of Feeder of Radio 100 000 Brown Black Yellow R2 Grid Bias of Feeder of Mixer
9. a 45 power tube transformer coupled 10 the out put of the detector The circuit is shown in Fig 10 A double type of volume control is employed which operates by varying the input from the antenna to the first radio frequency transformer and also the grid bias of the first two RF tubes Both controls are operated by a single knob but the grid bias control does not begin to operate until the volume is partically reduced by the antenna control The antenna volume control is a 20 000 ohm potentiometer bridged across the antenna transformer primary with the ground connected to the variable potentiometer contact The other section of the volume control consists of an 800 ohm potentio meter in series with the 170 ohm fixed resistor The purpose of the 170 ohm fixed resistor is to insure a minimum bias of about 1 5 volts on the control grid of the first two RF tubes The linear power detector is capable of large outputs and the 27 detector tube operates with a plate potential of approximately 250 volts and a normal bias of approximately 28 volts The grid is biased by means of a 15 000 ohm resistor in series with the cathode which is bypassed by a capacity of 9 mfds A 2 megohm grid leak and a 00025 mfd grid condenser are connected in parallel and in series with the grid These have nothing to do with the detector action but are used to prevent the secondary of the radio transformer from interfering with the operation of the phonograph pic
10. is set in such a position that the pointer has the greatest swing to the right the receiver is tuned to exact resonance with the station The meter which is mounted on the panel directly above the station selector dial is a milliammeter connected between the 390 ohm resistor in series with the cathode of the second R F tube and ground so that it measures the plate current 38D aun anD AEN TRANS 1 SET EC QNNM hay EN RETURN Fig 8 Stromberg Carlson 13 When the receiver is tuned to exact resonance with a station the plate current is less than it is when the receiver is not tuned to resonance so the pointer swings further to right at resonance than at other points When the receiver is tuned to a very strong signal the grid bias will of course be high as already explained and the plate current will be correspondingly less so the greatest swing to the right will occur when a strong station is tuned exactly to resonance Correct heater voltage for the 24 and 27 tubes also for the 45 power tubes is about 2 4 volts and for the filament of the 80 rectifier tube about 4 7 volts Plate voltage for the R F tubes should be approximately 145 volts with 235 volts on the plate of the 27 detector and 12
11. said about them Correct plate voltage for the radio frequency and first audio tubes is about 105 volts while the detector plate voltage should be about 35 volts with 180 volts on the plate of the power tube Correct grid bias for the radio frequency and first audio tubes is about 5 volts It is secured by 1500 ohm resistors connected between the cathode and ground of each tube The biasing resistors of the radio frequency tubes are by passed by 5 mfd condensers The power tubes are provided with a negative bias of about 40 5 volts by the voltage drop through the 500 ohm resistor in the power pack 1909007 LST RADIO TND RADIO The secondary of the audio transformer is shunted with a 1 megohm resistor to improve the tone quality The output of the last stage is coupled to the loud speaker by means of a 20 henry choke and a 2 mfd condenser while a high frequency cutoff type of audio filter is included in the audio output system The loud speaker is connected to the receiver by pin type jacks located at the rear of the chassis A magnetic pick up connection is provided for phonograph reproduction Turning the volume control as far as possible in a counter clockwise direction connects the pickup in the grid circuit of the detector tube Table No 2 gives the correct filament plate and grid bias voltages for the receiver with the Hi Lo switch in the two posi tions and with different line voltages Tests made on a receiver in go
12. 15 120 125 HI LO LO LO LO UX 280 Filament Voltage RMS 4 5 4 75 5 0 4 5 4 7 4 93 Voltage per anode RMS 236 0 248 0 259 0 236 0 248 0 258 0 Amplifiers Heater Voltage RMS 2 17 2 27 2 38 2 16 2 26 2 35 Plate 106 0 110 0 115 0 106 0 110 0 115 0 Grid Voltage 5 0 5 5 5 75 4 7 5 2 5 6 Detector Heater Voltage 5 2 11 2 22 2 32 2 1 2 2 2 3 Plate 39 0 40 0 42 0 38 0 40 0 41 0 Grid 3 25 3 5 3 75 3 25 3 5 3 75 Audio Output Tube Filament Voltage RMS 4 5 4 75 5 0 4 53 4 72 4 94 Plate 167 0 175 0 184 0 165 0 174 0 182 0 Grid 37 0 40 0 41 0 36 0 40 0 41 0 NOTE The grid voltage on the Ist audio tube will be slightly lower than that the amplifier secondary of the Ist audio transformer Stromberg Carlson 6 tubes due to the drop in the Grid bias for the R F tube is secured by three 1 500 ohm resistors one connected between cathode and ground of each tube A 10 000 ohm grid biasing resistor is connected between the cathode of the detector and ground while grid bias for the 71A power tube is obtained by the voltage drop through a section of the tapped res
13. 5 volts on the plate of the first audio amplifier Correct plate voltage for the power tubes is about 250 volts Correct C bias for the first and second radio amplifier is from 1 to 1 5 volts For the third R F tube it should be 1 5 volts with a grid bias of 7 volts on the detector 7 volts on the first audio tube and 48 volts on the power tubes Correct plate voltage for the automatic control tube is 45 volts with a C bias of 9 volts If trouble is experienced with the automatic volume control the volume control tube should be replaced with another tube which is known to be in good condition Either high or low emission of the volume control tube will cause unsatisfactory operation of the control If the emission is too great the grid bias on the first two R F tubes will be higher than it should be Stromberg Carlson 14 resulting in volume lower than normal while if the emission is low the pointer of the meter on the dial will not swing quickly to the right when a station is tuned to resonance and will be sluggish and slow in operation and the tube should be replaced AUTOMATIC VOLUME CONTROL UY 227 Stromberg Carlson Model 642 The three stages of radio frequency amplification in the model 642 employ 24 screen grid tubes The output of the third stage of radio frequency amplification passes to 27 detector of the grid bias type There is only a single stage of audio frequency amplification
14. 9 and 20 A Correct operating voltages are given in Table No 8 also a total of nine tubes are required the connections being as shown list of the tubes employed throughout the receiver in Fig No 15 TABLE No 8 Type Position A Volts B Volts C Volts Screen Grid Volts 35 Ist 2 4 150 170 3 35 15 Detector 2 4 150 170 10 12 80 90 27 Oscillator 2 4 85 90 10 15 80 90 35 Ist I 2 4 150 170 3 35 2nd 1 2 4 150 170 3 80 90 27 2nd Detector 2 4 190 215 20 25 80 90 45 Audio 2 4 250 45 50 45 Audio 2 4 250 45 50 80 Rectifier 4 8 325 350 Stromberg Carlson 24 PICKUP JACK PICK UP SWITCH R AMPLIFIER MIXER TUBE Ast AMPLIFIER T 2nd 1 F AMPLIFIER DEMODULATOR AUDIO OUTPUT TUBES C 10MH emm gt 009009 2 000000 DS gt Y 000000 Enea EE 009009 po BUNE 33 IMF 000000 0600000 WT ELECTRODYNAMIC LOUD SPEAKER SS POWER OUTLET POWER RECEPTACLE 7 RECTIFIER ON OFF TUBE SWITCH z 54 2MF POWER CORD Fig 15 Stromberg Carlson 25 Since these receivers are accurately adjusted at the factory there are few adjustments necessary after they are installed In case of necessity however these receivers may be aligned and adjusted in the same manner as any other superheterodyne receiver The equipment necessa
15. Ist and 2nd R F tubes from 2 to 3 volts 3rd R F tubes 1 5 to 2 volts for the detector about 28 volts and for the power tubes approximately 46 volts The screen grid voltages for the R F amplifier tubes should be about 60 to 65 volts 9 4 00 00000 gt i gt 0000 3 00 Y a m Stromberg Carlson 11 The antenna volume control varies the amount of energy flowing through the primary of the antenna coupler while the amplifier volume control varies the C bias on the control grids of the first and second radio tubes through the 800 ohm poten tiometer by varying the potential of the cathode with respect to ground A fixed resistance of 170 ohms is connected in series with the 800 ohm potentiometer to secure a minimum grid bias on the first two tubes of approximateiy 1 5 volts The grid circuit of the linear power detector is biased by a 15 000 ohm resistor in series with the cathode A 1 microfarad condenser is connected in parallel with this 15 000 ohm resistor to by pass both radio and audio frequencies Note that a 00025 microfarad condenser and a 2 megohm grid leak are connected in parallel and in series with the grid They have no effect on the detector action however but are used to prevent the secondary of radio transformer from affecting the operation of the phonograph pick up The model 641 is designed for use with either a magnetic sp
16. RADIO SERVICE MANUAL 18 STROMBERG CARLSON RECEIVERS MODELS 734 744 635 636 638 641 642 645 846 10 11 12 14 16 19 20 22 25 AND 26 The wiring diagrams and service data in The R T I acknowledges with thanks the this Manual covers the latest models of Strom co operation and help rendered by the Strom berg Carlson radio receivers In all wiring berg Carlson Telephone Manufacturing Com diagrams the complete connections are clearly pany in the preparation of this Manual All shown and the values of fixed condensers and re of the material in it was supplied by them with sistors are given as an aid in making service tests their permission for its use by R T I students RADIO AND TELEVISION INSTITUTE Inc CHICAGO This Service Manual is one of a complete series covering all service work on standard radio receivers It is not for sale and can be obtained only in connection with R T I Training in Radio Television and Talking Movies Copyright 1931 by R T I a 59 USA I employing the neutrodyne circuit detector and two stages of Stromberg Carlson Model 734 the model 734 receiver there is an untuned antenna coupling s will be seen from an examination of Fig 1 the filaments of stage three stages of tuned radio frequency amplification all of the tubes with the exception of the power tube in the last stage of audio frequency amplification are connected in series The 210 power tube in
17. aker assembly Balancing and neutralizing adjustments are made exactly the same as in other neutralized tuned radio frequency circuits The volume control adjustment is made by loosening the hexa gonal nut that holds the casing of the rear resistor to its mounting bracket and turning the volume control knob as far clockwise as possible and holding it in that position while the casing of the rear resistor is turned counter clockwise as far as it will go The hexagonal nut is then retightened so as to clamp the rear resistor to the casing securely to its mounting bracket The volume control adjustment should be made so that the pick up switch closes just before the volume control hits the stop when turned counter clockwise If this is not done the range of the volume control will be decreased and the signal will be cut off suddenly when the pick up switch operates before the volume control has reached the minimum MOVING MOUNTED ON RETURN SPEECH cone INPUT TRANSFORMER N FIELD N ci CONNECTOR HALF FIELD SUPPLY CORD Fig 6 Stromberg Carlson 10 Stromberg Carlson Model 641 Receiver The model 641 employs three stages of tuned radio frequency amplification using 24 screen grid tubes detector and 1 stage of audio amplification Grid bias detection is used with a 27 detector tube The single audio frequency amplifying tube is
18. and when the bias is greater due to a strong signal the plate current will be correspondingly less the least reading being when the receiver is tuned exactly to resonance with a station pick up jack and a pick up switch are provided and connected as shown in Fig 13 so the audio amplifier of the receiver may be used for phonograph reproduction manual volume control is also provided It consists of a potentiometer connected across the secondary of the first audio transformer with a movable Contact connected to ground As shown there are two stages of audio amplification the first employing a 27 heater tube and the second a pair of 45 power tubes in push pull Table No 6 gives the normal operating voltages for each tube and circuit The values found when testing a receiver with a high grade analyzer should agree approximately with the values given in the table TABLE No 6 Filament Plate Screen Tube Type Voltage Voltage Bias Grid Amplifiers 24 2 4 135 3 0 85 27 24 195 m 25 15 A Amplifier 27 2 4 115 ix 4 5 2nd A F Amplifier 45 2 4 245 pe 45 Model 16 Receiver The model 16 is designed for operation from a D C power line It employs three 24 screen grid radio frequency amplifiers and five tuned circuits the same as in the models 10 11 12 and 14 The detector is a 27 tube and its output is transformer coupled to a 27 first aud
19. cord phonograph with an automatic record changer Both are adapted for attachment of No 1 Stromberg Carlson remote control equipment Three 24 screen grid RF amplifiers and five tuned circuits are employed Two of the tuned circuits are incorporated in a bi resonator which serves to couple the antenna to the first radio amplifier tube A broad band transformer couples the first and second tubes together with a second bi resonator circuit between the second and third RF amplifiers and a single tuned RF trans former between the last radio frequency amplifier and the 24 screen grid detector The antenna is coupled to the first tuned circuit the same as in the models 10 and 11 receivers previously described 27 automatic volume control tube is connected in the cir cuit Its function is to maintain practically constant volume by regulating the grid bias of the first two radio frequency am plifiers The grid circuit of the volume control tube is supplied with signal energy from the third radio frequency amplifier Strong signals cause the automatic volume control tube to in crease the bias on the first and second RF amplifiers thus de creasing the volume The visual tuning arrangement which is shown in Fig 13 consists of a milliammeter connected between the cathode of the second RF amplifier tube and ground It Stromberg Carlson 20 reads the plate current in that tube This plate current is of course varied by the control grid bias
20. eaker or a dynamic speaker Either Stromberg Carlson No 14 or No 16 magnetic speakers are recommended while if a dynamic speaker is used Stromberg Carlson No 25 is designed to give satisfactory operation The receiver is designed for use with an antenna and ground A good average length of antenna for this receiver is 85 feet unless located near powerful stations which are impossible to tune out Lhen an antenna from 20 to 55 feet in length will give better results Stromberg Carlson Model 846 In the model 846 receiver there are three stages of tuned radio frequency amplification employing 24 screen grid tubes de tector and two stages of audio frequency amplification In addition there is a 27 tube employed as an automatic volume control The detector and first audio tube are also of the 27 type while in the second audio stage two 45 tubes are connected in push pull In the power supply an 80 full wave rectifier provides direct current for the receiver Stromberg Carlson 12 As it will be seen from Fig 8 the field of the dynamic speaker is supplied with direct current by a 80 rectifier and a power transformer entirely separate from the power transformer and rectifier supplying the remaining parts of the receiver 110 volt line connects directly to the speaker field supply trans former which has two secondaries One of these secondaries supplies the filament of the 80 tube while the other supplies voltage whic
21. h is rectified for the field of the speaker The primary of the antenna coupler is shunted with a 20 000 ohm potentiometer in series with a 10 ohm fixed resistor This point of the potentiometer is grounded The purpose of this potentiometer is to vary the sensitivity by reducing the input to the antenna coupler automatic volume control tube is connected so as to vary the grid bias on the first and second R F tubes and thus maintain practically the same volume for all stations The output of the third R F tube is connected both to the detector and to the volume control When the strength of the carrier wave of an incoming signal increases the volume control circuit tends to increase the grid bias on the first and second tubes In creasing the grid bias reduces the amplification so the volume re mains practically constant for all stations with the exception of very weak ones By changing the sensitivity control the volume may be set to many desired values visual tuning meter in series with the cathode of the sec ond R F tube provides a visual indication showing when the receiver is tuned to exact resonance with a station When a station is tuned in strong enough to operate the au tomatic control the pointer of the meter swings to the right the amount of swing depending upon the station signal The ceiver should be adjusted so the pointer swings as far to the right as possible When the tuning control
22. ich is a 71A and the rectifier tube which is the 80 Tuning is accomplished by a 4 gang condenser operated from a single control and the circuit is of the neutrodyne type As will be seen by an examination of Fig 3 the neutrodyne circuit is used and the detector is connected for the grid bias or plate rectification method of detection There are five separate secondary windings on the power transformer the first of which supplies approximately 2 3 volts for the heaters of the 3 R F tubes and the first audio tube The second supplies 2 3 volts for the detector heater only which is rather unusual the purpose being to reduce hum The third winding supplies 5 volts for the power tube in the last stage of audio frequency amplification the fourth one supplies the high voltage to the rectifier and the fifth one supplies low voltage for the filament of the rectifier tube The secondary winding supplying filament current for the detector is shunted with a 10 ohm potentiometer with its variable contact grounded for hum balance and the secondary supplyin the power tube is shunted with a 20 ohm potentiometer whic also has its variable contact grounded Table No 1 shows the correct filament plate and grid voltages with varying line voltages and the hi lo switch connected to the primary of the transformer in the different positions Stromberg Carlson 5 TABLE No 1 Line 105 110 115 1
23. io amplifier which in turn supplies a pair of 45 output power tubes connected in push pull THIRD RADIO AMPLIFIER FIRST RADIO SECOND RADIO AMPLIFIER AMPLIFIER FIRST AUDIO AUDIO AUDIO TUBE Ayoo OUTPUT TUBES OUTPUT TRANS PUSH Led TRAN SILENT KEY 9 3 SHORT ANT TN f tof SPEAKER Connector gt 5 r3 SS a CHASSIS BASE LOUD SPEAKER POWER OUTLET ON OFF HL d SWITCH 3 i t 53 03209 8 H 3 mU 3 38 ic 257 POWER CORD i eH TUBES 25 ie Stromberg Carlson 21 PICK UP JACK PICK UP SWITCH 58 FIRST RADIO SECOND RADIO THIRD RADIO DET PLATE AMPLIFIER AMPLIFIER AMPLIFIER FILTER f Tuees CONTROL NNA 4 OUTPUT 25 TRANS A Eu i 000000 000 1 A 000000 54 p 000000 f gt 000 000000 tach atin TO GNO BINDING POST CHASSIS BASE TRIP SWITCH LINE FILTER 19 380 Fig 14 Stromberg Carlson 22 The heaters of the 24 RF amplifier and of the detector and first audio amplifier also the filament of the power tubes are all connected in series as shown Since the power tubes require less filament current than the heaters of the remaining tubes a dial lamp is connected in parallel with the power tube filaments The receiver should never be o
24. istor in the power pack which gives a negative grid bias of about 40 5 volts The volume control consists of two resistors operated by the same control knob The first is a 10 000 ohm potentiometer shunting the primary of the antenna coupler with its variable contact grounded The second part of the control is a 10 000 ohm variable resistor shunted across the primary of the third radio frequency transformer which controls the signal strength REAR VOLUME CONTROL RESISTOR MAIN SHAFT supplied to the detector Both units are mounted on one shaft and are insulated from each other by means of an insulation collar at one end of the shaft The arrangement of the volume control is shown in Fig 4 To adjust the two resistors so they will operate together loosen the hexagonal nut that holds the casing of the rear resistor 16 each mounting bracket and turn the volume control knob clock wise as far as possible Next rotate the casing of the rear resis tance counter clockwise as far as it will go Next retighten the hexagonal nuts so as to clamp the rear resistor in casing securely to its mounting bracket taking care not to turn the resister casing when the nut is tight Stromberg Carlson Model 638 In this model there are four stages of tuned radio frequency amplification employing 27 tubes a detector of the grid bias type and two stages of audio amplification The first one em ploying a single 27 tube and the second two 71 p
25. k up A pick up switch is provided to connect a phonograph pick up in the grid circuit of the detector Throwing the switch to the phonograph position connects one terminal of the pick up jack to the grid of the detector and the other to ground Correct operating voltages for the receiver are given in Table No 3 Stromberg Carlson 16 TABLE No 3 Filament Screen Grid Plate Tube Type Voltage Voltage Bias Voltage lst Amplifier 24 2 4 60 65 2 3 135 145 2nd Amplifier 24 2 4 60 65 2 3 135 145 3rd Amplifier 24 2 4 60 65 1 5 2 135 145 27 2 4 ev 28 250 Amplifier 45 2 4 46 240 80 4 7 a 345 Model 645 The model 645 has eight tubes consisting of three 24 screen grid RF amplifiers 27 detector two stages of audio frequency resistance coupled amplification employing 27 tubes and two 45 power tubes in the output stage The receiver is designed for operation from a 105 125 volt DC supply line The filaments of all tubes are connected in series as shown in Fig 11 which shows the complete circuit for the receiver The negative supply line connects through the switch directly to one filament terminal of one of the 45 power tubes the filament return to the positive side of the line being made through a re sistor which lowers the voltage to a value which is suitable for the filaments
26. od condition should shows approximately the values given in this table RADIO oh 4 UST AUDIO DETECTOR HE ET AA Stromberg Carison 8 Fig 5 TABLE No 2 Line HI LO Filament Voltages Amplifier Detector Audio Output UX 280 Plate Voltages Detector sings eine soe caste eee een lst Audio Amplifier Audio Output UX 280 A C volts per anode Grid Bias Voltages Ist Audio Amplifier Audio Output Alternating voltage input to dry rectifier on loud speaker assembly Direct voltage across field coil of loud 115 120 125 HI HI 2 15 2 25 2 35 2 1 2 15 2 25 4 4 4 6 4 8 4 42 4 6 4 8 97 101 105 33 34 35 91 95 98 164 172 178 263 275 287 5 5 2 5 5 4 1 4 4 4 7 35 37 39 11 4 11 9 12 9 10 5 11 2 11 9 Stromberg Carlson 9 The loud speaker is of the dynamic type the connections being as shown in Fig 6 the field of the speaker is supplied with cur rent from one of the power transformer windings and a rectifier is included in the spe
27. or the 80 full wave rectifier tube and the fourth is the high voltage winding which provides plate and grid voltages for the receiver The values of all fixed resistors and fixed condensers are given on Fig 12 and the normal voltage reading for each tube and circuit are given in Table No 5 PICK UP JACK PICK UP SWITCH ANT FIRST RADIO SECOND RADIO THIRD RADIO AUDIO OUTPUT AMPLIFIER AMPLIFIER AMPLIFIER 1 DETECTO TUBES CONTRO be LDNG ANT SWITCH CONG ANT AUDIO AUDIO 3 INPUT TRANS OUTPUT TRANS SHORT ANT A lt gt C lt gt lt gt gt c gt c lt gt gt gt 5 SPEAKER CONNECTOR gt lt gt lt gt lt gt lt gt lt gt lt gt gt lt gt c c 5 gt e to E gt c gt C lt gt w lt gt lt lt gt lt gt lt gt 4 gt gt gt gt gt gt 9 313 5 ES CHASSIS BASE ng ELECTRODYNAMIC LOUD SPEAKER POWER OUTLET RECEPTACLE ON OFF SWITCH Stromberg Carlson 19 TABLE No 5 Filament Plate Grid Screen Tube Type Voltage Voltage Bias Grid Amplifiers 24 2 4 135 2 5 80 DETECTOR 24 2 4 200 pe 75 Amplifier 45 2 4 235 xa 45 RECTIFIER 80 4 8 ed Jus 2 Models 19 and 14 The same chassis and speaker are employed in the models 12 and 14 The No 14 however is equipped with a multiple re
28. out the pilot lamp the lives of the 45 power tubes will be shortened any one of the tubes burns out or is removed the filament of the remaining tubes will not light When a tube is to be removed from a socket the receiver should always be turned off on account of the fact that an are will form at the filament contact and may burn the prong or the socket Correct operating voltages for the filament heater grid and plate circuits of the various tubes are given in Table No 4 TABLE No 4 Normal Tube Type Filament Screen Grid Plate Plate Voltage Voltage Bias Voltage M A R Amplifier 24 2 1 56 5 107 1 0 Detector 27 2 3 13 05 lst Amplifier 27 2 2 25 79 1 10 2nd Amplifier 27 2 2 5 105 1 5 eoe ia 45 2 2 9 96 23 Models 10 and 11 Models 10 and 11 employ the same circuit the only difference being that the No 11 receiver is mounted in a console cabinet in which a phonograph panel assembly may be added making a combination radio and phonograph Three stages of radio frequency amplification are employed using 24 screen grid tubes There is total of five tuned cir cuits in the radio frequency amplifiers also a broad band inter stage coupling transformer Stromberg Carlson 18 Fig 12 shows a complete schematic diagram of the circuit employed in the models 10 and 11 As will be noticed the output of the third radio frequency amplifier supplie
29. ower tubes in push pull double volume control is provided consisting of two 10 000 ohm resistors the first of which is shunted across the primary of the antenna coupler with its mid point grounded while the second is connected across the output of the third radio frequency stage Both of these controls are mounted on the same shaft and op erated by a single knob on the panel of the receiver The three tuned stages of radio frequency amplification are neutralized by the adjustable neutralizing capacitators shown directly above the radio frequency tubes in Fig 5 One unusual feature of this receiver is the fact that a separate secondary winding is provided on the power transformer for the heater winding of the detector tube alone This winding pro dnces about 2 3 volts and has a 10 ohm potentiometer shunted across it with its variable contact grounded for hum balance The heaters of the three radio frequency tubes and the first audio tube are supplied with 2 3 volts from another low voltage secondary on the power transformer The third winding snpplies about 4 5 volts for the filament of the 71A power tube It is shunted by a 20 ohm potentiometer for hum balance the middle point of which is grounded Stromberg Carlson 7 The plate current for the receiver is obtained from 80 rectifier connected as shown in Fig 5 The values of the filter condensers and the resistors in the power pack are given on Fig 5 so nothing further need be
30. perated without the dial lamp because the filament of the power tubes will be overloaded and their lives correspondingly shortened As in other models of Stromberg Carlson receivers a phono graph pick up jack and pick up switch are provided the con nections being as shown in Fig 14 which is a complete schematic diagram of the receiver In Fig 14 the values of all fixed condensers and resistors are given as an aid in making tests All voltages for the receiver are supplied from the power line with the exception of the C bias for the output power tube This bias is provided by a 9 volt C battery The following table gives the normal voltage readings for the receiver The DC meters used to make these measurements should have a resistance of approximately 1000 ohms per volt These readings correspond to a line voltage of 120 volts on the high position of the Hi Lo switch of the voltage divider The voltages found upon actual test may not agree exactly with the figures given in the table but they should be approximately the same TABLE No 7 Filament Screen Grid Plate Tube Type Voltage Voltage Bias Voltage Amplifiers 24 2 4 60 65 2 2 5 95 100 E27 95 100 45 2 4 9 0 100 105 Ist AST cakes S 33 450 95 100 Stromberg Carlson 23 Stromberg Carlson Models 19 and 20 The same chassis is employed in the models 1
31. ry in proper aligning one of these receivers includes the broadcast signal oscillator inter mediate oscillator and output meter The frequency of the intermediate amplifier is 175 kilocycles The following table gives the resistor identification also the color coding of the resistors used throughout the receiver and will be helpful in service work COLOR CODING Designation FUNCTIONS Value Ohms BODY TIP DOT Grid Bias Feeder of Radio 500 Green Black Brown R2 Filter Resistor Plate Circuits of SC 600 Blue Black Brown R3 Filter Resistor Screen Circuits of SG 600 Blue Black Brown R4 Mid tap Resistor Heater Circuit at First I F Tube 3 Wire Wound R5 Demodulator Grid Bias 10 megohms Brown Black Blue R6 Demodulator Grid eese esses 100 000 Brown Black Green R7 Grid Biasing Resistor Power Output 750 Wire Wound R8 Mid tap Res Fil Circuit Output 10 Wire Wound R9 Series Grid Resistor of 500 Green Black Brown R10 Cathode Resistor of 6 500 Blue Green Red Cathode Resistor of Mixer 6 500 Blue Green Red R12 Filter Resistor Demodulator
32. s the grid of a 24 detector the output of the detector supplies a pair of 45 power tubes in push pull The phonograph pick up jack and the pick up switch are con nected in the grid circuit of the detector so that when a phono graph pick up is connected to the jack and the switch thrown to the phonograph position the detector acts as an amplifier thus giving two stages of amplification for phonograph records The antenna is capacitively coupled to the first tuned circuit There is a pin jack arrangement by which it is possible to con nect either of two capacitators in series with the antenna circuit to compensate for the antenna length The range control is provided to reduce the signal input from the antenna to the RF amplifier when extremely strong signals are received When the range control is thrown to the local position it shunts a 015 mfd condenser between the antenna and ground The volume is controlled by means of the 1000 ohm potentio meter marked R6 in Fig 12 Changing the setting of this potentiometer varies the grid bias applied to the first and second RF tubes the variations being from 3 to 15 volts A switch is connected in the primary of the power transformer to compensate for variations in the line voltage The secondary of the power transformer has four windings onc of which supplies the heaters of the detector and RF tubes another supplies the filament of the power tubes the third supplies filament voltage f
33. the last stage is supplied with 714 volts audio frequency amplification C current for its filament from a 7 volt winding on the The receiver is designed for operation either with a loop or secondary of the power transformer with an antenna and ground If operated with an antenna the Standard type 201 A or 301 A tubes are employed in the coupling stage is connected in the circuit but with loop operation R F stages and the first stage of audio frequency amplification the input from the loop is supplied directly to the grid circuit For the detector a 201 A or 301 A is used or if better sensitivity of the first R F amplifier is desired a detector of the 200A or 300 A type may be used ANT cor RAUO RECORD KEY s 23 IMPEDANCE eiue snc 7 AUDIO TRANSFORMER VST AUDIO ZND AUDIO COUPLING STAGE SEO RADIO DETECTOR T 1 Tove Set Wows ae AINE pe i 4594 gove 515 Fig 1 Stromberg Car son 2 RADIO RECORD KEY DETECTOR 00 IST AUDIO TUSCE E 15T RADIO ZND RADIO ES NC AUDIO TRANSFORMER 00025 3 AMF oA IMPLDANCE COR C Hvac At ADC 4SVt 30 37544 Fig 2 Stromberg Carlson 3 UY 227 OR PHONOGRAPH PICK UP JACK UY et1 OR 12 OR
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