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1947-48 Theatre Catalog, 6th Edition, Page 350 (336)

1947-48 Theatre Catalog, 6th Edition
1947-48 Theatre Catalog
1947-48 Theatre Catalog, 6th Edition, Page 350
Page 350

1947-48 Theatre Catalog, 6th Edition, Page 350

CLOSE-UP VIEW of the proiector mechanism and the- sound head. Note the quickly detachable, parallel action gate, the large diameter lens, and the built-in fire-extinguishing equipment with leaftype fire trap. The new equipment is an example of what was achieved by the concerted cooperation between Gaumont and Kalee scientists and engineers in the two fields of proiection, sound and picture.

H.T. and heater supplies are obtained from the main power supply panel on the rack. A meter panel also on the rack, measures, on one position of its switch, the total anode current of the amplifier.

Use with Duplicated Amplifier Channel.-When two or three amplifiers are used, each of the small control panels carries an itemergencyf switch, a film, disc, microphone switch, and a transformer stepping down to a 500-ohm line. The chance of an amplifier failing is admittedly remote, but in the event that this unlikely happening the emergency switch cuts out the defective amplifier and connects the photo cell output direct to the other, or one of the other, amplifiers. In this emergency condition, changeover is still not done on exciter lamps, but on the emergency switch of the amplifier. Any necessary repair work can be done at leiseure, without stoppage of or interference with the program.

The SOTO-ohm output lines are connected to a separate main volume control unit which also carries the changeover switch. Remote control units enable changeover or variation in volume level to be effected from two or three operating positions.

H.T. and heater supplies, when two or more amplifiers are used, are obtained from a separate supply unit, mounted on the rack. There is provision for metering the anode current of each ampli

fier. In emergency, H.T. and heater supplies can be obtained from one of the main power supply units.

Power Amplifier

The power amplifier is mounted on a standard cadmium-plated panel 20 inches wide which is carried on the rack in the vertical plane. Its height is 9 inches. All major items, valves, condensers, transformer are mounted on the front face. All the wiring is at the back of the panel. Every component is visible and identifiable, and can be detached or replaced without disturbing any other component. Every inch of the wiring can be inspected, and every wire can be traced from origin to destination. All the components are rated for continuous tropical use.

The amplifier comprises three stages, the power output of 30 watts being obtained from four tetrodes in parallel push-pull. Degenerative feed back is applied over the complete amplifier, from output to input.

The. first stage is a pentode. This is resistance capacity coupled to the second stage, a triode, working as a phase inverter. This phase inverter valve has fixed value of anode and cathode resistance, the circuit employed being one that eliminates the undesirable feature of manual balancing. The inverter stage is in turn resistance capacity coupled to the generous output stage. Thirty speech watts output is obtained from valves

which are run in comparison with makeris permissible rating. On full output, there is less than 11/2 percent of total harmonic distortion.

Bias to all stages is obtained in the most straightforward and trouble-free way, by the voltage drop across resistances in cathode circuits of the individ ual valves. Except for the output transformer, there is no iron-cored component in the panel. '

H.T. and heater current are obtained from a separate panel, the power supply unit.

The power amplifier and power supply unit have already been described. A' meter panel is mounted between them, and on the sevral positions of its selector switch gives a reading for total plate consumption of the voltage ampliner, of each of the first two stages of the power amplifier, of the four power output, tubes in pairs, and of the value of H.T. available. The meter, in each of the switch positions, should read in the region of 0.4, but by reason of the number of resistances, all of which must have a small tolerance, it is desirable with each installation to establish a normal reading for subsequent reference.

The power amplifier is designed to feed into an optimum load of 10 to 12 ohms. The impedance of the power stage, looking into it from the terminals of the output transformer, is 5 ohms.

Use in Single Channel Equipmentse When an amplifier forms part of a single amplifier channel, it is mounted in an imposing cabinet-type rack Which also houses a power supply panel, a meter pane], two exciter rectifier panels, a dividing network, and a connection panel. Access is provided to both sides of all the panels. It is recommended, wherever the size of the operating box permits, that the rack should be so placed as to leave behind it a clearance of 2 feet 6 inches. When necessary, this clearance may be reduced to a minitnum of 1 foot.

So far as running adjustments or the replacement of valves is concerned, it is only necessary to have access to the front of the panels, and this is given by a full-length door on the front of the rack. The backs of the panels are reached by detaching the rear covers of the rack.

Use in Duplicated Channel EquipmentsrvA dual channel is housed in two cabinet-type racks. Normally the two racks are placed close together to facilitate the wiring, but if the shape of the operating enclosure dictates such a course, they may be separated by any desired distance.

Each rack contains a complete amplifier channel, comprising an input panel carrying the necessary transformer to terminate the low impedance input line, a power amplifier, a meter panel, and a power supply panel. On one rack is a control panel which selects the channel to be used. The racks are completed by other panels, exciter rectifier, dividing network, and voltage amplifier, necessary to the function of a complete equipment.

Power Supply Panels

SO as V) cope with all main frequencies between 25 and 60 cycles, two different types of power supply unit, are produced. Were it not for the fact; that

1947-48 Theatre Catalog, 6th Edition, Page 350