Figure 7-29.--Schematic diagram of two stations in parallel.

is depressed, the voice coil leads of the loudspeaker are

from push-pull amplifier arrangements are high gain

and low distortion. Transformer coupling not only

shifted from terminals 7 and 13 of the secondary of T2

allows the amplifier to be isolated, but also provides

to input transformer T1 of the amplifier. Thus, talk relay

impedance matching between the input and the output.

K1 is operated, which applies plate voltage to the

amplifier at the talking station and places the amplifier

OPERATION

in the ready condition. The voice signals are amplified

and applied to terminals 14 and 15 of T2 at the listening

To call a particular station, depress the station

station and appear across terminal 7 of T2 and the

selector push button for that station, depress the talk

moving contact of volume control S25, and from there

switch, and speak directly into the reproducer grille.

to the loudspeaker. The amplifier in the listening unit is

Release the talk switch to listen. When the conversation

in standby.

is completed, depress the release push button to restore

The operation of two intercom stations in parallel is

the selector switch.

illustrated by the simplified schematic diagram in figure

To answer a call from another station, simply listen

7-29. The incoming speech from a remote station will

to the conversation, and answer by depressing the talk

be heard at both stations 3 and 3A, and replies can be

switch; it is not necessary to operate the station selector

made from either station. Either station can call a third

switch. The call light on your unit will be illuminated to

station, but both stations cannot call at the same time.

indicate your station is being called by another station.

When talk switch S26 at station 3 is depressed to

If the call light remains illuminated at the completion of

transmit a message, talk relay K1 at station 3A is

your conversation, depress the talk switch and remind

operated to open the circuit to the loudspeaker and

the calling station to depress the release push button.

prevent acoustic feedback (not shown).

The audio circuit between two stations is illustrated

Incoming speech lines 1 and 1C of station 3 are

by the simplified schematic diagram in figure 7-29. The

connected to terminals 15 and 14, respectively, on

talk switches at both stations are shown in the restored

transformer T2.

(listen) position. When talk switch S26 at either station

Figure 7-29.--Schematic diagram of two stations in parallel.

7-29