Western Electric 407A-4, Instruction Manual

Page: 19 / 136

a tube arcs back, an alternating current flows through the
shunt associated with the faulty tube and current flows
through the copper-oxide rectifier and associated relay,
thus opening the relay contacts and giving an indication on
the control panel of the particular tube which has arced
back.
Relay S7H is provided to indicate excessive current
drawn from the rectifier and to open the high-voltage cir­
cuit breaker.
Circuit
Relay S7H may be properly adjusted by passing 15 amperes
direct current through the resistahce R7H, setting the arma­
ture gap at 10 mils and the spring pressure of the back con­
tact at 10 grams, then decreasing R8H until the relay just
operates. If it operates with a maximum value of R8H, in­
crease the spring pressure or increase the armature gap.
The correct operation of relays SlH - S6H requires an
accurate adjustment of the relays and the proper function­
ing of the copper-oxide rectifiers XlH - X6H. To adjust re­
lays S2H, S4H and S6H, adjust the separation between the
heel piece and head plate to 1 or 2 mils. Make sure that
the armature moves freely without binding. Adjust the pres­
sure of the contacts at the bottom of the relays to 15 to
30 grams. With the relay operated the contacts should open
approximately 1
/
32 inch. Turn the screw in the face of the
armature so that with the relay operated the armature does
not make actual contact with the pole face but provides a
very small clearance. With the relay oper ated the distance
between the operating arm and stop should not exceed 1
/
32
inch.
Adjust relays SlH, S3H and S5H for an armature gap of
10 mils and a contact pressure of approximately 10 grams.
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