INTERCOM KEYING CIRCUIT.
a. Operating voltage. The intercom
keying circuit (Figure 5) operating
voltage 22-30 volts DC is applied from
pin B of J501 to the AM-1780 MAIN
POWER switch S504, and CKT BKR CB501.
It is then applied to the AM-1780
relay coils K501, K502, and K503. From
the relay coils, voltage is applied
to pin H of J504, J505, J506, and J507;
then through each CX-4723 to pin H
of J801 and pin C of J802 and J803 on
(Trace this on your
Intercom keying circuit operating voltage (+24 volts DC).