1570B AMPLIFIER

OPERATING INSTRUCTIONS

SPECIFICATIONS

Type: Gain: Input Sensitivity: Power Output: Frequency Response: Input Impedance: Source Impedance: Load Impedance: Output Impedance: Noise Level: Controls: Power Supply: Tubes: Dimensions: Color: Weight: Accessories: Power Amplifier 72 db 1.0 volt rms for rated output 175 watts at less than 5% thd, 65-20,000 cps 165 watts at less than 3% thd, 70-10,000 cps 1.0 db, 10-50,000 cps 70,000 ohm potentiometer 150, 600 ohms with 15095 Plug-in Transformer 8 (35v), 16 (50 v), 32 (70 v) ohms Less than 10% of nominal load impedance Output noise -25 dbm: 77 db below rated output Volume control, continuously variable composition 105-130 volts, 60 cps, 350 watts 1-12AX7,1-6SN7GTB, 2-6W6GT, 2-811-A, 4-5R4GY 10 1/2" H, 19" W, 13 1/2" D Green 59 lbs. 15095 Plug-in Transformer 10399 Panel
1515 S. Manchester Ave., Anaheim, Calif. New York

12969-1

PRICE $.14

LITHO IN U.S.A.

GENERAL DESCRIPTION
The 1570B Amplifier is a compact, high quality, 165 watt power amplifier designed for public address applications, either shelf or rack mount. Rack mounting occupies six units (IO1/2") of rack space. Negative feedback is carried around all stages from a tertiary winding on the heavy duty output transformer, permitting the output to feed an ungrounded load or a load with one side grounded. This amplifier is designed for stable 70 volt line operation under all output load conditions without impairment of program quality. Power switch, pilot light and gain control are located on the front of the amplifier and the input and output terminals, in the form of barrier type terminal blocks, are mounted on the rear. A six-foot three-wire power cord, terminating in a three-pin cap, is standard equipment with this amplifier. A special protective device is incorporated in the 1570B in the form of a thermal circuit breaker shunted by a power resistor, the combination being in series with one side of the power transformer primary. The breaker is fastened to the amplifier chassis so that heat from the latter is transferred to the breaker thermal element. AC line current through the breaker also heats the thermal element. Abnormal heating of the chassis and abnormal line current will make the breaker contacts open, inserting the power resistor in series with the power transformer primary reducing the voltage to it. Program service is thus maintained at reduced power. The breaker being an automatic reset type, reduction in line current and chassis temperature will allow it to close and restore full line voltage to the power transformer. Cycling will continue until the abnormal condition is corrected. Locating the amplifier in an inadequately ventilated, high ambient temperature zone will result in excessive heating. Overdriving the amplifier due to a mismatch of load to amplifier output will result in abnormal line current.

INSTALLATION

When mounting 1570B Amplifiers in a standard rack or cabinet rack, use a minimum of one rack unit (1 3/4") spacing between amplifiers and fill space with the 10399 perforated panel. When cabinet racks are used, a blower of approximately 40 cfm capacity should be installed on top of the cabinet to exhaust hot air from within the cabinet. Fresh air is thus drawn into the amplifier chassis through the front grill openings.

INPUT CONNECTIONS

Two pairs of input terminals are provided. Terminals 1 and 2, which connect directly to the input potentiometer, are provided for unbalanced high impedance sources or for bridging unbalanced low impedance lines having a signal voltage of 1 volt or more. Terminals 3 and 4 connect to a standard octal socket which permits low impedance input from balanced or unbalanced lines of 150 or 600 ohms with the accessory 15095 (plug-in) Line Transformer. The socket is connected for 600 ohm operation as shipped. The 150 ohm input is obtained by strapping the socket terminals as shown on the schematic. Both inputs may be used simultaneously provided the input to 1 and 2 is built out with a 100,000 ohm resistor in series with the high side of the line to prevent excessive loading or shorting of the low impedance input.

OUTPUT CONNECTIONS

Output taps for nominal loads of 8, 16, and 32 ohms (70 volt line) are provided. Connections and strapping are shown below.
Speaker Matching: Use the output tap which most nearly equals the total speaker impedance. If the load impedance falls between two output tap values, use the lower tap. 70 Volt Line: The constant voltage distribution system (70 volt line) permits connection of a large number of speakers, each to operate at the power level desired, without regard for the impedance involved. In this system, each speaker is equipped with a transformer which has a number of taps rated in terms of power and the tap is selected which gives the desired speaker power. The total power required for the speakers should be equal to or less than the amplifier power rating. Protection of Horn Loaded Drivers: In industrial paging systems, stadium, arena or other voice reinforcing systems which require excellent intelligibility over high noise levels, diaphragm type driver units coupled to horns are used. When these are used without loudspeaker dividing networks (used in two-way speaker systems), the low frequency energy applied to the driver voice coils must be limited. This protection is provided in the 1570B Amplifier by means of an R-C high pass filter in V-1 grid circuit (see schematic). As shipped, capacitors C9 and C10 are strapped out. By cutting one or both of these straps attenuation is introduced as shown in the table, depending on the impedance of the source. CPS
Source Impedance Cut Strap 1000 2000
100,000 Ohm Low (Approximately correct to

15,000 ohms)

B A A and B B A A and B
-4.0 db -3.0 -7.0 -5.2 -8.5 -12.5
-1.5 db -1.0 -2.5 -2.0 -4.0 -6.2
-.5 db -.3 -.8 -.7 -1.5 -2.5
-.2 d b -.2 -.3 -.2 -.5 -.7

POWER CONNECTIONS

The power transformer of the 1570B Amplifier has primary taps for 117 and 128 volts and is shipped with the 128 volt tap (white lead) connected. Use of the 128 volt tap for all line conditions will extend component and tube life, reducing maintenance to a minimum. Do not connect the 117 volt tap unless 24-hour line checks show that the line does not exceed 117 volts. For your convenience, these two leads are equipped with ring type terminals, the one in use being connected to one terminal of the interlock microswitch and the unused terminal insulated with plastic tubing.

POWER OUTPUT

When making power output measurements, connect a jumper across the terminals of the thermal breaker. Continuous sine wave output in the full power range may operate the breaker, giving false readings, if the jumper is not used. In motor drive or other applications which require continuous sine wave full power output of the 1570B, the thermal breaker should likewise be bridged out of the circuit.

CONTROLS

Two controls are provided: Volume control and AC power switch. Provision has been made for mounting an accessory relay to provide plate power keying by remote control. The mounting holes are located near the center of the chassis and are suitable for a PotterBrumfield type PR-3 relay or equivalent which should be mounted under the chassis. Select a relay having the desired coil voltage. If control wiring and microphone lines are carried in the same conduit, use a DC type relay. The white wire from the cable form to terminal 6 on V-9 tube socket should be transferred from this terminal to one contact on the relay. Connect the other relay contact to terminal 6, V-9 socket.

SERVICING

When the top cover is removed for tube replacement, etc., an interlock switch interrupts the AC line voltage to the power transformer. Do not attempt service work on this amplifier with AC line voltage on, as approximately 1,000 volt potentials occur at various points. Discharge all filter condensers before making continuity or resistance measurements. Routine servicing may then be done using the schematic for pertinent data reference. If high voltage measurements must be made, proceed with caution.

PARTS LIST

C1 C2, 3 C4, 5 C6 C7, 11 C8 C9 C10 R1 R2 R3, 21 R4, 5, 9, 10, 17 R6, 7 R8 R11, 12 R13 R14 R15, 16.0002 mfd. 10%, 600v ceramic, Erie GP2-331.22 mfd., 400v, Astron BP4-22.1 mfd., 600v, CD PM6 P 1 40x40 mfd., 500v, Mallory FPmfd., 200v, Mallory FPmfd., 1000v, Tobe-Deutchmann TAB-1006 ,0056 mfd. 10%, 600 v ceramic, Erie 811.0022 mfd. 10%, 600v ceramic, Erie GP-ohms 10%, 1/2 watt 330,000 ohms 5%, 1 watt 100,000 ohms 10%, 1/2 watt 100,000 ohms 10%, 1 watt 2.2 megohms 10%, 1/2 watt 1800 ohms 10%, 1/2 watt 330,000 ohms 10%, 1/2 watt 82,000 ohms 10%, 1/2 watt 600 ohms, 5 watt, Ward Leonard Type ohms 10%, 1/2 watt R18 R19 R20 P1 BR1 PL1 T1 T2 L1 L2 S1 S2 RS1, 2 V1 V2 V3, 4 V5, 6 V7, 8, 9, 10 75,000 ohms, 20 watt, Ohmite Brown Devil 5 ohms, 50 watt, Ohmite 0400A 10 ohms 10%, 1/2 watt Altec Lansing 12435 Klixon CA3 Thermal Breaker G.E. Mazda #44 Peerless 16492 Peerless 6410 Peerless 17173 Peerless 17266 Altec Lansing 12763 Interlock, V3-1 Microswitch G.E. 1N1695 Silicon Rectifier 12AX7 Vacuum Tube 6SN7GTB Vacuum Tube 6W6GT Vacuum Tube 811-A Vacuum Tube 5R4GY Vacuum Tube

OPERATING INSTRUCTIONS

SPECIFICATIONS
Type: Gain: Input Sensitivity: Power Output: Frequency Response: Input Impedance: Source Impedance: Load Impedance: Output Impedance: Noise Level: Controls: Power Supply: External Power Available: Tubes: Dimensions: Color: Weight: Special Feature: Accessory:
Power Amplifier 65 db 0.9 volt 40 watts at less than 2% thd 40 to 20,000 cps 1 db, 5-30,000 cps; 4 db, 1-100,000 cps 70,000 ohm potentiometer 150 or 600 ohms with 15095 Plug-in Transformer 4 (12.6 v), 8 (18 v), 16 (25 v), 124 (70 v) ohms ungrounded Less than 15% of nominal load impedance 80 db below rated output Volume control, continuously variable, composition 117 vac, 50/60 cycles, 125 watts 117 volt ac receptacle on chassis 2-6CG7, 2-6CA7/EL34, 1-5U4GB 8 3/4" high, 19" wide, 7 3/4 deep Dark green 22 lbs. Two stage high-pass-filter for protection of horn loaded drivers 15095 Plug-in Transformer

GENERAL DESCRIPTION

The 1568A Amplifier is a rack mounted, AC operated power amplifier intended for use in sound reinforcing, paging, music distribution, or any application requiring low distortion, wide frequency range, complete stability with any type of load, reliability of operation, ease of servicing or low cost. At 40 watts distortion is less than 2% at any frequency from 40 to 20,000 cycles per second. The frequency response is within 4 db of mid range value from 1 cycle per second to 100 KC. The feedback circuit is designed for stability under conditions of varying line voltage, varying tube characteristics, and all types of loads including long unloaded speaker lines having considerable capacitance. The tubes are conservatively operated under CCS (continuous commercial service) ratings of their manufacturer, and the amplifier has been shown to withstand "hot switching" and other punishment which might be encountered in the hands of untrained operators. The amplifier occupies five units of rack space (8 3/4") and has a hinged front panel on which are mounted the power switch, fuse, pilot light and a continuously variable gain control. All circuitry is completely accessible for servicing when the front panel is open. The amplifier is equipped with a 3-wire power cord terminating in a 3-pin cap. Input and output terminals are provided in the form of barrier-type terminal blocks mounted on the outer surface of the chassis.

INPUT CONNECTIONS

The 1568A Amplifier is equipped with two pairs of input connections. Terminals 1 and 2, connecting directly to the input potentiometer, are provided for unbalanced high impedance sources, and to bridge unbalanced low impedance lines having a signal voltage of 0.9 volt or higher. Terminals 3 and 4 connect to a standard octal socket which accommodates the accessory plug-in transformer. With the 15095 Transformer, balanced or unbalanced lines of 150 or 600 ohms up to a level of +15 dbm may be connected to input 3-4. The octal socket is normally connected for 500/600 ohm operation; 150 ohms impedance may be obtained by strapping the terminals in accordance with the diagram shown on the schematic.

OUTPUT CONNECTIONS

Outputs accommodate nominal loads of 4, 8, 16 and ohms, the corresponding full-drive output voltages being 12.6, 18, 25 and 70 volts. Speaker Matching: Use the output tap which most nearly equals the total speaker impedance. If the load impedance falls between two output terminal values, favor the terminal of lower impedance. 70 Volt Line: The 70 volt distribution system permits connection to a large number of speakers, each to operate at its own power level as required, without the necessity for computing impedances. In this system each speaker is equipped with a transformer containing a number of taps rated in terms of power, and the tap is selected which gives the power desired for that speaker. The total of the power settings for all speakers should be equal to or less than the amplifier system power rating. The 1568A Amplifier is equipped with outputs to drive both a 70 volt line and a 25 volt line. Protection of Horn Loaded Drivers: Driver loudspeakers coupled to horns are used in paging or voice reinforcing systems where excellent intelligibility is required in the presence of high noise levels, effects of wind, and other disturbances. When a loudspeaker system dividing network is not available the diaphragm of the driver loudspeaker may be protected from low frequency power by the use of the R-C low frequency cut-off filter in V1 grid circuit (see schematic). As shipped, capacitors C1 and C2 are strapped out. By cutting one or both of these straps attenuation is introduced as shown in the table, depending upon the impedance of the source. Effect of High Pass Filter Source Impedance 100,00 ohms Low Strapping One strap cut Both straps cut One strap cut Both straps cut 250 - 6.5 -16 -13 --3 -8 -8 --1 -3.5 -3.5 -4.cps -0.2 - 1. 2 -1.2 - 1. 5 db db db db

CONTROLS

The only controls on this amplifier intended for normal operation are the power switch and the gain control. Potentiometer P2, which establishes the bias voltage for the output tubes, is set at the factory and will probably not require readjustment over a long period of operation. If, due to ageing of the rectifier, the bias voltage should drop below the value indicated on the schematic, it will be desirable to reset P2. Measurement should be made with an accurate voltmeter, at a line voltage of 117 volts, and with no signal applied.
FREQUENCY IN CYCLES PER SECOND

PARTS LIST

C1 C2 C3 C4 C6, 7 C8 C9, 10 C11 R1, 8, 12, 13 R2 R3 R4 R5, 6 R7 R9 R10, 11, 18.002 mfd. 10% ceramic disc Erie 811-202.001 mfd. 10% ceramic disc Erie 811-mfd. 6 V. MalloryTT.000047 mfd. 10% ceramic disc Erie 831-470.22 mfd. 400 V. Sprague 4TMP-mfd. 50 V. MalloryTC 40 x 40 mfd. 500 V. Mallory FP288.5 mfd. 400 V. CD PJ4P5 100,000 ohms 10% 1/2 watt 47 ohms 1% 1/2 watt deposited carbon 1800 ohms 10% 1/2 watt 100,000 ohms 10% 1 watt 68,000 ohms 10% 1/2 watt 1 megohm 10% 1/2 watt 18,000 ohms 10% 1 watt 47,000 ohms 10% 1 watt R14, 15 R16 R17 R20 R19 P1 P2 F1 PL1 S1 SR1 J1 T1 T2 V1, 2 V3, 4 Vohms 10% 1/2 watt 600 ohms 5 watt Ohmite Brown Devil 1500 ohms 1 % 1/2 watt deposited carbon 220 ohms 10% 1/2 watt 4700 ohms 10% 1 watt 200,000 ohms Altec Lansing ohms Mel-Rain Type FFF-amp. 3 AG fuse Mazda #44 Altec Lansing 12536 switch Selenium Rectifier GE1N1491 Alden 402 ACEHG receptacle Peerless 16432 Peerless 6288 6CG7 vacuum tube 6CA7/EL34 vacuum tube 5U4GB vacuum tube