Figure 6-15.--Schematic diagram of the sidetone circuit.

receiver, you complete a dc circuit through the

Capacitor C1, varistor RV1, and resistor RB

switchboard, which operates relays to disconnect the

constitute an impedance balancing network for the

ringing generator and connect you to your calling

line impedance. Capacitor C1 also compensates for

party.

the line capacitance. Capacitor C2 prevents dc

voltages from being extended to the receiver.

Preventive Maintenance

Varistors RV1 and RV2 comprise a gain control

Preventive maintenance for the version 2 set is the

to maintain a constant input and output level

same as for the version 1 set.

regardless of whether the telephone is connected to a

long or a short loop. Resistor R1 is a current-limiting

Corrective Maintenance

device to protect varistor RV1 from high line-voltage

Corrective maintenance of the version 2 set

surges.

includes adjustments and replacement of failed

Varistor RV3 acts as a click suppressor and is

components.

almost a short circuit across the receiver when the

ADJUSTMENTS.-- There are four adjustments

voltage across RV3 reaches approximately 1 volt.

on the type G (version 2) telephone set: the hookswitch

This action also prevents demagnetization of the

contact springs adjustment, the ringer adjustment, the

receiver.

gong adjustment, and the dial illumination lamp inten-

SIDETONE CIRCUIT.-- Figure 6-15 is a

sity adjustment. Dial illumination lamp intensity on the

simplified schematic diagram of the receiver sidetone

version 2 set is adjusted in the same manner as the

circuit. Because current will not flow through a

version 1 set. Dial speed on the version 2 set is not

balanced circuit, the turns ratio of inductors L1 and

adjustable; therefore, if the dial speed is too slow or too

L2 is unbalanced by a predetermined amount and the

fast, the dial must be replaced.

value of resistor RB is changed so as not to match the

Hookswitch Contact Springs.-- Figure 6-17 is

line impedance. This way, a controlled amount of

an illustration of the hookswitch assembly. To adjust

signal can be induced into L3 to be used as receiver

sidetone.

R I N G E R CIRCUIT.-- The ringer can be

connected to the telephone line for one- or two-party

service. Figure 6-16, views A and B, illustrates how

the telephone set is connected for the service desired.

For two-party service, ringing is extended to the

prime telephone set over the R (L2) lead and to the

extension set over the T (L1) lead.

When a caller dials your number, the ringing

generator located in the automatic dial telephone

switchboard applies 75 to 100 volts ac at 20 Hz to the

ringer of your telephone set through capacitor C1 (fig.

6-13), causing the bell to ring. When you pickup your

Figure 6-16.--Type G (version 2) ringer connectors.

Figure 6-17.--Hookswitch assembly.

Figure 6-15.--Schematic diagram of the sidetone circuit.

6-17