this is the Model 15
Contents
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7. 2 RED 250 1 35 HH 70 GSIS AMPLIFIER 9 36 9 H G 80 RECTIFIER __ 8 1 5 7 H 3s 24 5 ia 3 2520 2 4 624 6245 5575 G 47 5 Fit Continuity Chart Model 15 Chassis 103007 sissey do r urrojsue1 4 Y 0 109310 3 051 50 209 udo 81 Pinous 45315 1 2 stag 4 puz 81 7 ON LI PIJIN 107 PUP 5000 40136162 WYO 000 00 93214 103999 so o udo H 91 PON SI apoye PRA t su puoo pue 0006 o YH ai ON l Ja E ee L g gt puz yo 0 wado YH oe gt NE 202123 ON
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10. Terminals are provided on the Models 15 and 23 chassis for antenna and ground con nections Antenna and ground terminals are located at the rear of the chassis and clearly marked Normal antenna length should be approximately 30 to 40 feet When the receivers are to be operated in localities several hundred miles distant from broadcasting stations a longer antenna is recommended In such cases where consistent long distance reception will be required antenna length should be approximately one hundred feet COLOR CODE Power Transformer Model 15 Primary Start of Winding Y ellow Finish of Winding Yellow Start of Anode Yellow Center Tap Anode Black Finish Anode Red Start of Heater Yellow Finish of Heater Yellow 280 Fil Start Black 280 Fil Finish Black Model 25 Primary Start of Winding Yellow Finish of Winding Yellow Start of Anode Center Tap Anode Biack Finish of Anode Red Start of No 1 Heater Black Finish of No 1 Heater Black Start of No 2 Heater Yellow Finish of 2 Heater Yellow Start 5 v Fil Black Center Tap No 1 Heater Red Finish 5 v Black 6 JPW AInuyuUoD SLNIOd 1531 00002 aalan 1 0 GA POWER AMPLIFIER 8 12 gt i re 5 6 24 5 2ND DETECTOR 4 8 4 42 ENO
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12. Y 14 IPPON 03 JO MAJESTIC 75 ZC OSCILLATOR FIG 96 SHIELOEO VOLUME our Pur 4882 WITH 2222 CONTROL TO GRID 1 CONTROL GRID OF 755 DET METAL 14000 CASE 27 SHIELD BNO GROUND ALIGNING SWITCH ey SER SPEAKER CONE THERMO GALVANOMETER OR 7 44 5 85 PLATES TRANS INSTRUCTIONS LE TRANSFOR MER SHOWN N ABOVE OSCILLATOR SWTABLE FOE 175 C OPERATION MAY BE PURCHASED FROM GEIGS GPUNOW THROUGH THE OSTH OPERATION WEERT TE PLUG IN OSCILLATOR SOCKET PLACE 9 27 OSCILLATOR TUBE TAKEN FRO CHASS S MOLISE OSCILLATOR SOCKET 547 OUTPUT METER SWITCH TO _ SPEAKER POSITIOW 25746 TUBE 15 WARN CLOSE CIRCUIT SWITCH ADJUST VOLUME OUTPUT CONTROL 70 GIVE OW SCALE READING ON OUTPUT METER ALIGN LE STAGE IN CHASSIS TO PESONANCE 2 MAXIMUM READING ON OUT PUT METER NOTE 22 TOF SHOUD BE CHECKEO SEP ORE USING PLUGGING IN ON A STANDARD CHASSIS AND MAL NS GRIGSBY GRUYOW EHICAGO UEA 2 WITT SN ODBIO OD MONNIO AISDIAD 2 FL SNHO OGLI 2797 waxes 22222224 93 2 4257 tp
13. fore any attempt is made to make any necessary corrections of alignment GRIGSBY GRUNOW Technical Data for Pertaining to Model 15 Model 25 Chassis The Circuit MODEL 15 The Model 15 Chassis employs the superheterodyne circuit espe cially designed to give full performance with the minimum n of tube stages The circuit from antenna to speaker is arranged as follows fir t detector stage inter mediate frequency amplifier stage second detector and pentode power amplifier stage In cluding the rectifier five tubes are employed in the Model 15 Chassis The Model 15 superheterodyne circuit differs from the customary superheterodyne circuit employed in compact receivers in that the design of the pre selector input circuit gives an image ratio that gives this receiver perfect freedom from heterodyne interference 5 2 MODEL 25 The Model 25 Chassis employs the efficient superheterodyne circuit de signed with a greater number of tuned stages to give the characteristics of uniform high sensitivity single channel selectivity 10 kcs and nearly perfect audio frequency response The circuit from antenna to speaker is arranged as follows pre selector stage oscillator first detector stage intermediate frequency amplifier stage second detector twin power detec tion and push pull pentode power amplifier stage Nine tubes are employed in the above mentioned stages The Model 25 super
14. some of the principal problems that have been holding back the design of high sensitivity receivers with the requisite tone quality Off and Line Switch The off and on switch on both the Model 15 and 25 is attached to the volume 5 control shaft Turning the volume control completely to the left shuts the receiver off The first fifteen degrees rotation of the contro to the right will turn the receiver on The balance of rotation to the right controls the volume of the receiver Models G 10 B G 11 B and G 13 Dynamic Speakers The Model G 10 B Dynamic Speaker has field resistance of 1750 ohms at 78 The Model G 10 B Dynamic Speaker field structure is of the heavy U construction This speaker is used in conjunction with the Majestic Superheterodyne special cone The 11 and G 13 Speakers employ the same structure as the G 10 B but are used in conjunction with larger size cones to match acoustic properties of the cabinets in which they are employed The Model G 10 B Speaker employs a hum bucking coil as an additional aid in the filter system in the Model 15 chassis This coil consists of a small winding around the field coil and is connected in series with the cone coil This winding induces hum into the cone coil circuit in opposite phase to any hum that passes the filter system The effect is a cancellation which reduces hum to a minimum in the speaker Antenna and Ground Terminals
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16. SERVICE MANUAL Technical Data Pertaining to Model 15 Chassis Model 15B Chassis Model 150 Chassis Model 25 Chassis 1931 Model 15 Chassis is Employed in Havenwood Ellswood and SHerwood Models Model 15B Chassis is Employed in Fyfewood Model Model 150 Chassis is Employed in Castlewood Phonograph Combination Model Model 25 Chassis is Employed in Brentwood Chelt nwood and Brucewo d Models GRIGSBY GRUNOW COMPANY CHICAGO U S A The information contained in this Manual applies to _ Majestic Models 15 and 25 Superheterodyne receiver chassis The completely new design and progress shown in these two super heterodyne Receivers warrants your careful perusal of this Manual so that you may become fully acquainted with what is considered the outstanding achievement in present day Superheterodyne Re ceivers The Engineering Laboratories of the GRIGSBY GRUNOW COMPANY have incorporated in these Receivers every available improvement known to present day radio science It is to your advantage therefore to fully familiarize yourself with the char acteristics of this circuit so that you may intelligently render re quired service for the benefit of the customer in obtaining the exc llent performance of which these Receivers are capable There are several aligning adjustments on the 15 and 25 Chassis and it 15 imperative that this Manual he followed as to aligning procedure b
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19. coustic a STATIG MODIFIER VOLUME CONTROL STATION SELECTOR AND OFF SWITCH LF ALIGNING CONDENSERS CONDENSERS OSCILLATOR POWER TRANSFORMER ANL Top View Model 15 Chassis ST PPOR OPIS vano 7 61 PPOR VOLUME CONTROL AND OFF SWITCH A STATION SELECTOR 900 ANT STAGE Bottom View Model 15B Chassis ACOUSTIC CONTROL VOLUME CONTROL STATIC MODIFIER CON ANO OFF SWITCH ALIGNING CONDENSERS POWER TRANSFORMER OND ANT View Model 158 Chassis 34195840 ST PPO 9 0 ima woog a a Poio ESTAN 40103139 vous 230 Guy 1 22 6 OSN ODODIHD 02 MONNYD AGSOIYD 5 606 46 SWHO OSL si 97914 A SORE WAH 71 7948556 2 BAMA 304677 250 04285 90 15 AT 8130 sis D 2 AIZSNIINOD E HLIM SLLOIM YIMOd 537040 O9 OS ONY 52 SL7I0A OEZ 511 S ISS9HD OS
20. heterodyne circuit differs from the regular super heterodyne circuit employed in the customary receivers in that the design of the detector stage provides an almost perfect fidelity of signal through the detectors to allow an audio frequency output from the speaker of faithful tone reproduction Method of Biasing Model 15 The necessary bias is obtained on the first detector and oscillator stage through a 10 000 ohm resistor between cathode and ground The intermediate frequency amplifier is biased through the volume control and a balance resistor of 264 ohms which is contained in the volume control The second detector is biased through a 40 000 ohm resistor to ground in the cathode circuit Model 25 The radio frequency amplifier first detector and intermediate frequency amplifier are biased by the volume control and a balance resistor of 160 ohms contained in the control which is in the cathode circuit of these tubes The twin power detectors are biased in their grid circuit by a 250 000 ohm resistor to ground Volume Control System Model 15 Control of volume is obtained in the Model 15 chassis by a 11 500 ohm control which controls the bias of the oscillator first detector and I F amplifier stages This control is so arranged in the circuit that in addition to controlling the bias of these two tubes it controls the input voltage to the pre selector stage simultaneously s that a balanced control system is obtained M
21. more or less perma nent and should not need further adjustment except in rare cases IN ALL ALIGNMENT PROCEDURE AN OUTPUT METER MUST BE USED R F and Oscillator Alignment 28 1 Tune in station in the vicinity of 1500 kilocycles or output of local oscillator if available into receiver 2 Align stage and oscillator tuning condenser The stage and oscillator aligning condensers are on the gang condenser Oscillator Tracking Condenser Alignment 1 Tune in local oscillator to 600 kilocycles 2 Adjust both tuning control and tracking condenser simultaneously to give maximum signal as noted on output meter This will be obtained by rocking tuning control across resonance point while adjusting tracking condenser to give maximum output at the point of resonance This operation cannot be performed without local oscillator and output meter Check Check the alignment previously made of and oscillator aligning condensers in the vicinity of 1500 kilocycles New G 27 S G 24 S and G 51 S Spray Shield Tubes The new Majestig Spray Shield Tubes are a distinct advancement in the art of tube design The principal advantages of the Spray Shield Tube are as follows 1 More efficient shielding of each circuit 2 More amplification possible per tube stage 3 Regeneration reduced to a minimum 4 Improved tone quality due to absolute stability of the amplifier stages The above advantages overcome
22. odel 25 Control of volume is obtained in the Model 25 chassis by a 6500 ohm control which controls the bias of the radio frequency amplifier first detector and intermediate fre quency amplifier stag s Sensitivity In cases where low sensitivity is encountered the first step taken to remedy the condi tion should be the checking of the radio frequency type G 51 and G 51 S Tubes Tubes having a low amplification factor in any of these positions will seriously affect the sensitivity of the receiver These procedures should always be taken prior to any attempts at remedy by realignment of the condenser gang Power Supply System Model 15 The power supply system of the Model 15 chassis consists of a power trans former filter unit and dynamic speaker field The filter unit contains two 8 mfd especially designed dry electrolytic condensers and the speaker field which acts in the capacity of a choke Model 25 The power system of the Model 25 chassis consists of a power trans former filter unit and dynamic speaker field The filter unit contains two 8 m d especially designed dry electrolytic condensers a liberally designed choke and the speaker field in addition Alignment In checking the alignment of the Models 15 and 25 chassis the intermediate frequency transformers should not be aligned unless there is definite reason to believe that they are out of alignment The alignment of these transformers at the factory is
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