Western Electric 407A-4, Instruction Manual

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shut off completely if the inlet temperature exceeds 165
degrees.
A sudden or excessive rise of water temperature indi­
cates a failure of the cooling circuit due to : (a ) improper
valve settings, (b ) blower motor failure, or (c ) clogging of
the radiator by leaves, paper, etc.
The immediate remedies for such failure are : (a ) read­
justment of valves ; (b ), (c) starting second cooling unit
blower and diverting all hot water through second radiator ;
then (b ) repairing motor failure or (c ) cleaning radiator by
washing it down with a hose from inside .
Oscillators
RADIO-FREQUENCY CIRCUITS
D-99110 Oscillator-Amplifier
(Unit A, Schematic Figure 7 )
Circuit
The carrier frequency of the transmitter is supplied
by either one of two 702A oscillators, which are mounted in
the slide rail assemblies in the upper compartment of the
oscillator-amplifier unit.
All connections to the oscillator units are made by
means of spring contacts which engage when the units are
properly inserted.
Each oscillator contains the quartz crystal Yl, the
vacuum tube Vl, and associated circuits, and the temperature­
control circuit consisting of the heater resistance �6 and
thermostat TDl.
The intermittent operation of the heater and thermostat
maintains the crystal at a constant temperature. Power for
the heater is obtained through the transformer T7A and is
supplied as soon as power is connected to the t ransmitter,
irrespective of its operation. Lamps ElA and E2A indicate
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