Eddystone S870 Receiver
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This is another of those
AC/DC Eddystone receivershat depend on complicated mechanical
arrangements to keep the live chassis from contacting the outer
case. Because an earth connection is made through a condenser
C4, it's highly desirable to use a third mains wire, the safety
earth connection which ensures the outer case or the aerial/earth
wires can never be live. |
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A couple of top views
of the chassis showing the 4 valves plus rectifier. A twin gang
tuning condenser shows the set has no RF stage in front of the
frequency valve.Note extra wiring that's been added for an external
speaker. The speaker wiring is isolated from the chassis but
has a condenser C47 so some measure of tingling could be felt
by an unwary user. |
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The receiver uses a set of valves
which are satisfactory with series connected heaters: 12BE6 Frequency
changer, 12BA6 IF amplifier, 12AT6 audio amplifier/Detector/AVC,
19AQ5 audio output and a 35W4 HT rectifier. The total heater
requirement is 90 volts so the remainder for 110 volt operation
is 21 volts. This is accommodated by using a pair of dial lamps,
a ballast resistor and a thermistor.
Under the chassis you can see
a sizeable flywheel and a neat arrangement of coils and beehive
trimmers. |
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Being an AC/DC receiver means no
mains transformer and so voltage sellection is done via a high
wattage ballast resistor. This is designed to work correctly
given the current consumed by the circuit. |
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The manufacturer's plate tells us
that this set is an S870 from around 1956 rather than the later
"A" version from around 1963. |
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