INSTRUCTIONS FOR INSTALLING, SERVICING AND OPERATING GATES SA SERIES EQUIPMENTS I SA7 POWER SUPPLY SA8 VOLUME INDICATOR SAlO MONITORING AMPLIFIER SAl 7 SWITCH AND FUSE PANEL SA20 PROGRAM AMPLIFIER SA22 CUEING AMPLIFIER SA66 GENERAL PURPOSE AMPLIFIER SA70 PRE-AMPLI FI ER SA7l PRE-AMPLIFIER SA72 PRE-AMPLIFIER SA77 POWER SUPPLY SA78 POWER SUPP,LY SA79 POWER SUPPLY INSTRUCTIONS FOR INSTALLING, SERVICING AND OPERATING GATES SA SERIES EQUIPMENTS SA7 Power Supply SA8 Volume Indicator SAlO Monitoring Amplifier SA17 Switch and Fuse Panel SAZO Frogram Amplifier SA22 Cueing Amplifier SA66 General Purpose Amplifier SA70 Preamplifier SA71 Freamplifier SA72 Preamplifier SA77 Power Supply SA78 Power Supply SA79 Power Supply I.B. 804 Copyright 1948 by GATES RADIO COMPANY Quincy, Illinois INDEX Page General detail on SA Amplifiers ..; .............................................. 1 and 2 SA-66 .................................................................................... 3,4,5 SA-66 Resistor Board Drawing .................................................. 5 SA-66 Electrical Characteristics ................................................ 6 SA-66 Parts List.. .................................................................. .. . 7, a SA-66 Pictures (with parts indication). ................. . ....................... 9, 10 SA-66 Schematic.. .................................................................... 10 SA-20 Frogram Amplifier .......................................................... 11, 12 SA-20 Farts List ....................................................................... 12, 13 SA-20 Pictures (with parts indication). 14 SA-20 Resistor Board Drawing ................................................... 15 SA-20 Schematic ..................................................................... 15 SA-10 Monitoring Amplifier ....................................................... lb,17 SA-10 Electrical Characteristics ................................................ 18 SA-10 Parts List.. .................................................................... 19, 20 SA-10 Pictures (with.parts indication) ......................................... 21, 22 SA-10 Schematic 22 SA-22 Cueing Amplifier ............................................................. 23 SA-22 Farts List ....................................................................... 23, 24 SA-22 Pictures (with parts indication) .......................................... 25 SA-22 Schematic.. ...................................................................... 25 . SA70, SA-71, SA-72 Preamplifiers .............................................. 26, 27 SA70 Parts List.. ........................................................................ 28 SA70 Pictures (with parts indication) ............................................ 29, 30 SA70 Schematic ......................................................................... 30 SA7 Power Supply ...................................................................... 31 SA7 Farts List ......................................................................... 32 SA7 Pictures (with parts indication) .............................................. 32, 33 SA7 Scheniatic .......................................................................... 33 SA77, 78, 79 Power Supply and Parts List ........................................ 34 SA77 Picture and Schematic ........................................................... 33 SA8 Volume Indicator Panel ........................................................... 35 SA8 Volume Indicator .................................................................... 35 SA8 Pictures (with parts indication) ................................................. 36 SA8 Schematic 36 SA17 Switch and Fuse Panel ............................................................ 37 SA17 Parts List ........................................................................... 37 SA17 Pictures (with parts indication) ................................................ 38 SA17 Schematic ............................................................................ 38 GENERAL DETAIL ON SA SERIES AMPLIFIERS 6 The SA series of amplifiers have all been designed around a uniform plan so that no matter what amplifiers you might purchase they will wire to- gether and fit together with ease and symmetry of appearance. The Gates SA series developed during the Gates Silver Anniversary Year, thus de- riving the SA prefix, are indeed America’s finest amplifiers for precise requirements in FM and AM broadcasting. Engineers will appreciate the extras in the SA series such as the completely new type of panel design for complete parts accessibility without removing from the rack or cabi- net. They will appreciate the extra shields in the input transformers for extreme low noise and the large power transformers and chokes. for no more than 40 degree Centigrade temperature rise inside of a rack cabinet. A service pilot light has been provided to illuminate the inside of the amp- lifier housing. This is 6.3 volts and connects to an amphenol socket on the side of the housing. By an external’6.3 volt source or the Gates SA17 switch and fuse panel the inside of the housing may have sufficient light in the darkest corner to service the equipment where required. Jacks are used for checking current of each tube. Jacks were selected to eliminate long wiring lengths which are required with pushbuttons and quite often troublesome in FM installations. The tip of the phone plug is (lr6 positive and Gates has provided a handy test set for use with SA amplifiers, though any standard volt-&meter may be used with a milliammeter scale. The SA series of amplifiers have been carefully packed; in fact, packing is part of Gates engineering. If the equipment arrives damaged, place claim with the transportation company at once and return for repair or replace- ment on your order form. It is well, where possible, to locate equipments having larger tubes and power transformers near the top of the cabinet, but this is not mandatory, other than it is always considered good engineering practise. For ease in servicing, various circuit voltages will be found on each schematic dia- gram. Equipment failure will be eliminated with good maintenance by the operating staff. Dirt, dust and grime are the chief equipment trouble- makers. Keep the equipment clean. Tube sockets may be cleaned by moving the tubes in and out of the sockets several times. Noise often reported in amplifiers in the form of popping noises will nearly always result in either corroded tube socket prongs or noisy tubes themselves; over 90% of all amplifi~ers returned to the factory for service actually have no greater defect than poor tubes. It is suggested that when a tube is suspected that the amplifier be given a complete new set of tubes. The cost is small and the results are great in satisfactory performance and satisfied management. -I- When testing amplifiers for response, noise and distortion always analyze the unit to be tested. Resistive input and output loads are most desirable as inductive loads will often cause a resonant circuit, indicating poor 4 response and at times, high distortion. Be sure distortion measurements are not made at a greater output level than the amplifier is rated. Also be certain the input is clean and that the oscillator itself has negligible distortion as well as hum. Hum, if excessive, will show up as distortion as well as noise. Noise measurements should always be taken at near the maximum output rating of the amplifier. Good test equipment is de- sirable in every radio station and Gates engineers will gladly make sug- gestions where desired as to recommended test apparatus. A word about changes. Each Gates SA amplifier has had hundreds of hours of engineering applied. It took nearly a year for several engineers to design a relatively few SA amplifiers. In case of trouble may we sug- gest no circuit or parts chanies in these fine amplifiers, as they are proven equipments designed by some of America’s finest engineers. Instead we suggest that first you make certain the trouble is the amplifier if trouble exists. The accessory attached or the circuit used in cokecting several amplifiers together can cause much trouble and often points an accusing finger at the amplifier which is usually not the offender. Be sure the SA amplifier you use is-intended for the purpose for which it is being used. A redesign of the circuit or parts is never the answer. You are installing the finest amplifiers than engineers have yet learned how to design. Maintenance is important, as every radio engineer knows. Regular periods (at least once each week) to check tubes, clean the equip- ment and make any other adjustments necessary will pay large pvidends and often times save embarrassment to operating personal. YOU may use your SA amplifier with full and complete security. No voltage has been .applied that is at maximum tube rating other than filament voltage. Trans- formers are so built that they may operate for weeks without turning off if be. All parts are conservative in rating for the purpose intended. We suggest when unpacking your SA amplifier that you check it over for loose bolts and nuts and look over the equipment to be sure there are no broken connections. Certain sections of express and freight cars devel- ope high degrees of viabration and niether you nor us know how the equip- ment was handled in transportation---so--look it over thoroughly before using. Gates engineers will gladly answer any questions you may have about this or other Gates equipment or help you plan a complete audio or trans- .mitter installation. Thank you for selecting Gates equipment for your needs. You have selected the finest. ~- I GATES RADIO COMPANY ----------- QUINCY, ILL.USA -2- INSTRUCTIONS SA-66 GENERAL PURPOSE AMPLIFIER ac, SECTION I - The Gates SA-66 is a versatile, three stage, high fidelity amplifier used for recording, monitoring and line amplifier service. The amplifier has been designed with four major usages in mind: 1 - High quality program amplifier 2 - Recording, monitoring or audition amplifier 3 - A complete V.U. meter range set 4 - Switchability to the above services without patching. SECTION II - The SA-66 uses three audio stages, with the following tubes: 6~5 triode, first audio, 6SN7 dual triode, second audio and phase inverter, and pushpull 6L6’s in output stage. Provision is made for two input impedances, one a 500/600 ohm balanced circuit and the other a bridging input. This bridging facility enables the amplifier to be installed across a line without disturbing the electrical characteristics of the line. Either input is selected immediately by the use of the input selector switch (Sl) located on the left side of front, panel. The two input circuits are terminated on terminal board marked TBl. Terminals #l and 2 are bridging input, #3 is ground and #4 and 5 are a 500/600 ohms input. Under “Electrical Characteristics” other impedance connections are listed for terminals 4 and 5. The output impedance of the SA-66 Amplifier has been designed to normally work into a 500/600 ohm load. The output transformer (T2) has a tapped secondary which makes it possible to change the output impedance to work into several different impedances normally used in audio work, 250 ohm, 75 ohm, 15 ohm and 5 ohm. See drawing AO-3033. By means of output selector switch. (S4) located on the front panel any one of three separate outputs may be selected. Output marked line is used for feeding a program loop, the output being fed through a 20 Db H pad directly to terminals #8 and 9 qn TB2. Output #l is direct from amplifier and terminated on #10 and 11; output #2 is also direct from amplifier and termin- ates on #12 and 13. Outputs #l and 2 can be used in various manners, such as driving recording heads, feeding one or more speakers, etc. The maximum recommended input level for the SA-66 Amplifier, if used as line amplifier (Sl in line position), should not exceed -10 V.U. If used as bridging amplifier (Sl in bridge position) the input level should not exceed $20 V.U. The SA-66 is capable of delivering t38 V.U. (6.3 watts) at very low dis- tortion figures to a correctly matched load. The SA-66 is capable of qp -3- delivering t40 V.U. or 10 watts (at -28 VU in) at slightly higher dis- tortion figures. When 54 is in line position the output is lowered by approximately 20 Db by use of an “H” pad inserted between output transformer and terminals 8 and 9 on TB2. The overall gain of the SA-66 is approximately 68 Db (checked at -30 V.U. in, +38 V.U. out). The frequency response of the SA-66 amplifier is essentially flat from 30 cycles to 15,000 cycles. The average variance will not be more than one DB over this frequency range. The distortion measurements of the SA-66 are held within 1% for the frequency range 50 cycles to 10,000 cycles, measured at t38 V.U. output. With an input of -30 V.U. and output of t38 V.U. the noise measurement should be 70 Db below program output level. SECTION III - The cast aluminum housing has standard rack.mounting dimensions, being 19 inches wide and 10-l/2 inches high. The total depth behind the panel is 10-l/2 inches. This unit will mount in any style rack or cabinet having the standard 19 inch mounting dimensions. The cast aluminum door and panel assembly is so designed that the amplifier may be used in any standard cabinet, with or without decorative style strips, and suffer no mechanical disadvantage. SECTION IV - The SA-66 is a completely self-contained, readoyp teor ate i , amplifier. It is shipped with its complement of tubes in their respective sockets. The installation of the SA-66 may be accomplished in any manner accept- able to the operating engineer. Due to the fact that the SA-66 uses the large V.U. meter, it is very desirable to locate the amplifier in the rack at approximately eye level. will be apparent that on the complete line of SA audio equipment the low level inputs are located on the left side as viewed from the rear and the high level outputs and A.C. are all grouped along the right side of the equipment. This has been done to enable the various units to be interwired in a practical manner, thus making the completed rack as noise free as possible. SECTION V - The SA-66 amplifier operates from 110/115 volts A.C. source. The power consumed is approximately 120 watts. The operation of this amplifier is conventional in all respects. Attention is again called to the permissible maximum input signal which should not be exceeded. The illuminated V.U. meter is used normally to check the output level of the SA-66 Amplifier. However, by the use of switch (S3) the V.U. meter and its associated range switch (R22) may be disconnected from the output of the SA-66 and brought out to terminals #6 and 7 on TB2. In this manner the V.U. meter can be used for any external measuring or testing. Input ‘1 -4- to V.U. range set is 7500 ohms for bridging across a 500/600 ohm circuit. SECTION VI - The Gates SA-66 amplifier requires very little maintenance other than routine. The SA-66 has individual metering jacks for each tube * enabling the engineer to read tube plate currents at will. C~athode or plate current of each tube measured at the jacks are as follows: Jl - 1.8 Ma. J2A - 1.6 MEL. J2B - 1.8 Ma. J3 - 57 Ma. J4 - 57 Ma. All tube currents will vary with tube condition and line voltagev, athriuasn ces of as much as 10 would not be unusual though J3 and J4 should read nearly identical for output stage balance. Service failures will be minimized if the equipment is maintained conscien- tiously by the operating staff. The amplifier is protected by a fuse (Fl) in the primary of the power transformer, in case of a component failure. A heater type rectifier is used which minimizes the starting surge voltage in the ampli- fier. For ease in servicing various circuit voltages are indicated on the schematic drawing C-15953. All voltages are measured from the ground buss with a vacuum tube voltmeter. -5- ELECTRICAL CHARACTERISTICS OF SA-66 GENERAL PURPOSE AMPLIFIER The specification tabulated below is the result of a standard laboratory test made on type SA-66 General Purpose Amplifier. These tests were made according to the standard laboratory test procedure with no extra attention being paid to any particular test other than the usual amount of precautions. They will, however, vary as to tube and line voltage condition and a decibel from that shown below is not objectionable. GAIN TEST Input z = 500 ohms output z = 500 ohms Input Level = 30 vu output Level = t40 vu Gain = 70 Db FREQUENCY RESPONSE Input output 30 50 100 1 Kc 5 Kc 10 I& 15 Kc 20 Kc -30v u t4ovu -0.2 0 0 0 0 to.2 t1. t2. DISTORTION IN ‘$ Input output 50 100 400 1KC 5Kc 7.5 Kc 10 Kc 15 Kc -30 vu t40 vu -32 VU t3a vu 0.91 0.52 0.34 0.34 0.77 1.2 1.55 1.9 0.62 0.52 0.34 0.34 0.56 0.67 0.76N OISE 1T.3E5S T Input -30 VU output t40 vu Noise -73 Db Noise is 75 Db down from a t40 VU base with level control at maximum attenuation INPUT TRANSFORMER Tl . For 500/600 ohms connect 1 and 6 joining 3 to 4 For 250 ohms connect to 2 and 5 joining 3 to 4 For 50 ohms connect to 2 and 4 joining 2 to 3, 4 to 5 Note: Changing from 500 ohms as wired affects accuracy of bridging pad Rl, R2, R3. -6- PARTS LIST SA-66 AMPLIFIER Drawing Description inc”I Symbol Fuseholder, #341001 (1075-S) Littlefuse Al Trouble Lamp Socket #505, Dialco (or equiv.) A2 Trouble Lamp Bulb, 6-8. volt #40 G.E. A3 30 mfd 475 volt plug-in type Industrial Condenser Cl Co., (or equivalent) 30 mfd 450 volt, FP-145 Mallory c2 20 mfd 450 volt, FP Mallory c3 Same as c3 c4 c-15937-14 25 mfd 50 volt, TC-36 Mallory c5 c-15937-15 .l mfd 600 volt DT-6Fl C-D c6 c-15937-14 Same as c5 c7 c-15937-15 same as c6 C8 c-15937-15 same as c6 c9 c-15937-17 .0025 mfd 800 volt MD-8D25 C-D Cl0 C-15937-16 40 mfd 150 volt BR-4015 C-D Cl1 c-15937-17 Same as Cl0 Cl2 c-15937-17 Same as Cl0 Cl3 Capacity depends on frequency response - will Cl4 be drawn by Testing Lab. Fuse, 3 amp Type 3 AG Littlefuse Jack, closed circuit, #2-A, Utah-Carter Same as Jl Same ?s Jl J2B Same as Jl J3 Same as Jl J4 Jack, #701 (Junior) J5 V.U. Meter, Model 862, Scale B, Weston Ml c-15937-7 10 K ohm 1 watt 10 ? A-B Rl c-15937-7 10 K ohm 1 watt 10% A-B e R2 c-15937-4 560 ohm 1 watt 101 A-B R3 Control, 250 K ohm #2900 Shallcross R4 c-15937-5 2700 ohm 1 watt 10% A-B .a ‘R5 c-15937-11 82 K ohm 1 watt 10% A-B R6 c-15937-9 18 K ohm 1 watt 10% A-B R7 R8 c-15937-13 470 K ohm 1 watt 10’: A-B R9 c-15937-5 2700 ohm 1 watt 10 7 A-B RlO c-15937-11 82 K ohm 1 watt 107 A-B Rll c-15937-5 2700 ohm 1 watt 101 A-B R12 c-15937-11 82 K ohm 1 v&t 10% A-B R13 c-15937-7 10 K ohm 1 watt 10% A-B R14 C-15937-12 150 K ohm 1 watt 10% A-B R15 C-15937-8 12 K ohm 1 watt 10% A-B C-15937-12 150 K ohm 1 watt 10% A-B c-15937-3 180 ohm 10 watt Wirewound -7-