| Indoor D.C. Trembler bell, with Church style gong, used on fire alarm
systems.
The early Bells are wooden cased whilst the later bells from 1955 are
plastic cased. The wooden cover is secured by means of two flat brass
side hooks.
Bell 40A - Twin 50 ohm coils, 2-10 volts - used on London Fire Brigade systems.
Bell 40B - Twin 250 ohm coils, 10-50 volts - used in PO buildings and specified
for omnibus call-bell systems.
Fitted with Bell-gong No. 21 (4.5in diameter x 3.1in - Church style).
Winding Specification
-
The
coils
shall
be
wound
with
wire,
copper,
enamelled
to
B.S.S.
156.
The
conductor
diameter,
turns
and
resistance
for
the
coils
are
shown
in
the Table
below.
-
The
inner
and
outer
coil
ends
of
the
Bell
No.
40B
shall
be
led
out
with
4/0.006
stranded
copper
wire,
double
silk
covered.
The
colours
of
the
covering
shall
be
red
for
the
inner
end,
and
green
for
the
outer
end.
-
Lead-out
wires
are
not
necessary
for
the
inner
and
outer
coil
ends
of
the
Bell
No.
40A.
-
The
coils
shall
be wound
anti-clockwise
-when
looking
at
the
yoke end.
-
The
windings
shall
be
protected
with
two
layers
of
cloth,
yellow
varnished
to
Specification
M1011
-
secured
by
an
approved
cement.
-
The
resistance
of
each
coil
shall
be
shown
on a
paper
label
beneath.
|
Bell
No. |
Conductor
diameter |
Turns
(each
coil) |
Resistance
(each
coil) |
| 40A |
0.0108
ins. |
3,460 |
2.5
ohms |
| 40B |
0.0068
ins. |
6,000 |
12.5
ohms |
Found in the Rate Book 1947 and 1956.
GPO Engineering Instructions on Fire Systems
Diagram - N640.
Drawing - 90487.
Specification - S524.
Picture of wooden Bell taken 1937. Plastic cased bells date from
1955.
|