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1947-48 Theatre Catalog, 6th Edition, Page 351 (337)

1947-48 Theatre Catalog, 6th Edition
1947-48 Theatre Catalog
1947-48 Theatre Catalog, 6th Edition, Page 351
Page 351

1947-48 Theatre Catalog, 6th Edition, Page 351

the cost of the 25-cycle unit is considerably greater than that of the 50-cycle unit, there would be no point in making two types, because the 25-cycle type is entirely suitable for use on any frequency from 25 to 60 cycles. In fact, in certain overseas areas, where both 25- and 50- or 25- and 60-cycle mains are encountered, it is the companyis recommendation that the 25-cycle unit should be installed in all cases so as to reduce the number of different components it is advisable to carry as depot spares.

The tw0 units are basically similar and assemblded on the same size cadmium-plated panel, 20 inches Wide by 12 inches high, for mounting on the rack in the vertical plane. All components are mounted on the front face of the panel, with all wiring in one plane on the back face. Either unit, under the most severe tropical conditions, has a safe output for continuous service of 250 milliamperes at 380 volts. All condensers used are of the paper dielectric type with a working voltage of 750 at a temperature of 140 degrees Fahrenheit (60 degrees Centigrade).

Two hard thermionic rectifiers are employed, but the valve holders are so wired that, when a valve is inserted, its anodes are strapped together. Each valve, therefore, behaves as a half-wave rectifier, the two together working as a full-wave rectifier.

One power supply panel is intended solely for operation from 50- or (SO-cycle supplies. The three transformers, high tension, rectifier filaments, and 6.3-v01t supply for valve heaters, have untapped 230-volt primary windings. Irrespective of the mains voltage, which may be of any value between 95 and 130 volts, or between 190 and 260 volts, a 230-volt supply is available by adjustment of the transformer contained in the separate switch fuse distribution unit.

Very generous smoothing is provided by a two-section choke input filter circuit. The choke input circuit gives much better regulation of the smoothed d.c. output, against varying load, than could possibly be obtained with a condenser input circuit. Two heavy-duty 7-henry chokes are employed, and each choke is followed by a capacity of 16 microfarads, formed of two 8-microfarad blocks in parallel.

There are three high-tension positive output terminals, of which two feed the poWer amplifier, and the other feeds the voltage amplifier.

The other power supply panel is primarily intended for operation from 25cycle supplies, but can be employed universally for 25-, 30-, 40-, 50-, or GO-cycle supplies. Its single transformer has three secondaries for high tension, rectifier filaments, and 6.3-volt supply for valve heaters. The primary is in two sections. which are put in parallel for connection to a 115-volt supply of any frequency from 25 to 60 cycles. The sections are put in series for connection to a 230volt supply of any frequency from 25 to 100 cycles. The transformer in the switch fuse distribution unit is adjusted to give either .115 or 230 volts, irrespective of the actual mains voltage.

The same degree of smoothing is provided as on the 54, but because this power supply panel has to contend with frequencies down to 25 cycles, the choke


input filter circuit has three sections. The additional section comprises a 30henry choke and an 8-microfarad condenser. This extra smoothing is effective on the output terminals.

Duosonic Speaker Assembly

The Duosonic speaker assembly renders the utmost fidelity in reproduction and, with its associated frequency-dividing network, gives a conversion efficiency of the order of 50 percent, an extraordinarily high figure. The frequency response range exceeds that of the medium film or disc, upon which the sound is recorded, and the whole assembly is, therefore, well suited to the faithful rendering of the output of the system as a whole.

Various models of the Duosonic speaker assembly are available in combina FULL LENGTH ABC LAMP DOOR, open on the operating side (above), reveals the 16-inch reflector. quick carbon holders, magnetic flame control. Controls are grouped on a rear panel.

tions of treble and bass horns, adapted to the size of the theatre auditorium.

The bass horn is constructed of fireproofed timber, complete with baffle surround.


Two monitor speakers may be provided, each with its own on-off switch. The volume of sound output from each is adjusted at the time of installation to be representative of the sound volume in the auditorium. This unique feature secures true monitoring, as distinct from a mere aural indication that the system is in operation.

In very large installations, a separate amplifier of 10 watts undistorted output is provided for monitoring, leaving the main amplifier free to serve the auditorium.

ON THE NON-OPERATING SIDE (below) can be seen how the mechanism is removed as a single unit. The layout is simple and parts accessible. Interior lighting is controlled by a door switch.

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1947-48 Theatre Catalog, 6th Edition, Page 351