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1947-48 Theatre Catalog, 6th Edition, Page 349 (335)

1947-48 Theatre Catalog, 6th Edition
1947-48 Theatre Catalog
1947-48 Theatre Catalog, 6th Edition, Page 349
Page 349

1947-48 Theatre Catalog, 6th Edition, Page 349

THE OPERATING SIDE, with all doors open. emphasizes the extreme accessibility to all working parts for service, maintenance and operation. and cleaning. The interior of the soundhead is finished in hard, white porcelain enamel. The magazines and magazine doors are of cast aluminum.

i-anipere type, and the photo cell is a normal gas type on a standard British 41-pin base.

The complete soundhead is immune to rust. The soundhead and the plate upon which is assembled the scanning unit are of cast aluminum of heavy section. The three bearing housings are die castings. The exciter lamp mount, the prism mounts, and the condenser mount are all die castings, as are the cell housing, slit unit plate, brackets for lay on roller and pad rollers, and the strippers. The lay on roller is nitrided steel, and small rollers and retaining screws are either of stainless steel or chromium-plated steel.

Voltage Amplifier

All units of the Gaumont-lialee 21 amplifier chain are built on 20sinch wide cadmium-plated flat panels for mounting in the vertical plane. The plating renders them rust-proof and ensures in perpetuity perfect metallic contact with the panel of all components mounted thereon.

The voltage amplifier is assembled on a panel 20 by 9 inches. All valves and components are on the front face, with connecting terminals projecting through to the back, on which side, in one plane, is all the wiring. Every component is rated for continuous tropical use.

The voltage amplifier may be mounted with the control panel at the bottom, or the whole frame may be inverted so that the control panel is at the top. Local conditions will dictate which way round (is most convenient, although control panel at top will probably be found to be the most generally useful. There is


provision for bringing conduit into the frame at both top and bottom.

The cabinet rack carries the 80vterminal panel at the top, and all conduit goes via the 63 trunking box to the top of the rack. The conduits act as a rigid brace for the rack.

Schematically, and in total number of components for a complete amplifier, it is extremely simple, comprising nothing more than three valves, resistance capacity coupled. There is no input or output transformer, and apart from the three valves and valve holders, there are only the requisite coupling and decoupling resistances and condensers. H.T. and heater supplies are obtained from the main rack.

The input valve is a pentode. The other two valves are triodes. This disc input is taken to the second stage. The tone control unit is electrically in the grid circuit of the third stage. Degenerative feedback is applied to the last tw0 stages.

The tone control gives independent control of bass and treble response, and is a self-contained unit which is readily detachable from the panel. Of deliberate design, access to this unit can only be obtained from the back of the panel. From the front of the panel all that is visible of it is its metal shroud.

The amplifier is housed in a wall mounting case which is carried on a hinged frame. Access to the valves is obtained by removing the detachable cover. Access to the back of the panel is instantaneous by undoing a catch and swinging the panel door open on its hinges.

The opening portion is hinged to a

THE NON-OPERATING SIDE is seen with the doors open to arc lamp. In the pedestal are seen the drive and automatic cut-off for the motor in the event of fire, and also the position of the spare gas cylinder. The covers of the motor housing are removed. Note the fire-fighting equipment.

rigid frame fixed solidly to the wall, and this fixed frame is of sufficient length to accommodate, under a detachable cover, a small control panel which carries equipment closely associated with the amplifier.

The amplifier is used in two different ways. With a single channel amplifier system, one only is mounted between the projectors. With a duplicated amplifier channel, an amplifier is mounted on the wall adjacent to each of the two, or three, soundheads.

Use with Single Channel Amplifier.When only one 52 amplifier is used, the components on the small control panel are the main fader (volume control), the changeover switch, and the film, disc, microphone switch. The photo cells are linked to this control unit by coaxial cables, and the changeover switch connects either the left or right hand cell through to the grid of the input valve of the amplifier. The changeover is noiseless and the method chosen permits any or all adjustments to be made on the soundhead not in use without interference with the program. The main fader is 22-stud, clickaaction type, completely enclosed, with a total resistance of 40,000 ohms. The output of the 52 amplifier goes by way of this fader and from the fader is conveyed on a coaxial cable, enclosed in a conduit, of course, to the input of the power amplifier. There is no transformer at either end of this line.

There is provision for mechanically coupling the control unit to a remote control, so that both changeover and variation in volume level can be effected from the operating position of either machine.
1947-48 Theatre Catalog, 6th Edition, Page 349