PM300 SERIES OPERATING AND SERVICE MANUAL Manufactured by SHURE BROTHERS INC. 222 Hartrey Avenue Evanston, Illinois 60204 U.S.A. Copyright 1978, Shure Brothers Inc. AL 407 (RE) 27A822 Printed in U.S.A.
PM300 SERIES SPECIFICATIONS Amplifier Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . All silicon transistor power amplifier Power Output . . . . . . . . . . . . . . . . . 100 watts continuous (RMS) to 8 ohm load (see Figure 3, Page 4) Voltage Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 db (8 ohm load) Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FIGURE 1. 2 FIGURE 2.
DESCRIPTION The Shure Power Master is a solid state booster power amplifier capable of delivering 100 watts RMS to an 8-ohm load. It has been designed specifically for use in conjunction with the Shure VA300-C and VA302-C Series Vocal Master Amplifiers. When used as a booster amplifier in conjunction with the Shure Vocal Master Amplifier, the Power Master will effectively increase area coverage, provide higher sound levels and increase reserve power.
The Power Master does not use speaker output match- ing transformers and thus avoids the distortion, power loss and added weight inherent in such transformers. The speaker output voltage is 28.3 volts, to an 8-ohm load, for 100 watts. This allows long speaker lines with wiring practices consistent with those used for 25-volt speaker lines.
6. Resolder the red-black lead wire to the solder-lug to which the green-black transformer lead wire is already attached. 7. Reinstall the bottom plate. 8 . Remove the four screws from the nameplate on the handle end of the amplifier. Turn the nameplate over and reinstall. The nameplate nomenclature will now be suitable for 120 volt use. To change the PM300E back for use with 240 volt power, reverse the above steps.
Bottom Removal: To remove the chassis bottom plate, turn the amplifier upside down and remove the ten screws located at the edges of the chassis. Cover Removal: For servicing of the components on the top of the chassis, remove the two screws on the handle end of the cover, and the two screws within the plastic feet nearest the bottom on the other end of the cover. Uncoil the A.C. line cord from the storage spindles and slide off the cover.
Diodes: Diodes D5 and D6, see Figure 5, Page 6, are located on the black finned sinks with the output transistors. Special care is required to insulate these diodes from the heat sink while providing good thermal transfer from sink to diode. Heat shrinkable tubing or “spaghetti” should be placed over the diode and connecting leads; the diode should be securely clamped to the heat sink with the clamp provided.
REPLACEMENT PARTS LIST FOR PM300 SERIES AMPLIFIERS ** Replacement Kit Consists of: Item Repl. Kit No. Qty. Part No.
NOTES TO THE CIRCUIT DIAGRAM PM300 CIRCUIT DIAGRAM D.C. Voltage Measurements: Check the DC voltages before checking AC voltages because transistors Q2 through Q9 are direct coupled and any deviation from the nominal voltages will affect the AC voltages. The four key DC voltages are +94, +20, the emitter of Q1, and the split voltage at the junction of R3, R5, R7, and R8. If these four key DC voltages are correct, then proceed with the AC voltage measurements.
PM300E POWER SUPPLY CIRCUIT DIAGRAM FIGURE 8. PM300E6 POWER SUPPLY CIRCUIT DIAGRAM FIGURE 9.
