Figure 2-11.--Type JA switch.

moving between positions. Open circuit problems have

forms over the contacts, which is only broken down if

been eliminated in this manner. The blade arrangement

appreciable voltage and power are available in the

provides for a circuit between two adjacent contacts,

circuit. However, in sound-powered telephone

such as in the 2JR switch previously discussed. The type

circuits, there is insufficient power to break down the

2JF has two such blade arrangements per switch deck.

film, and relatively high resistance results. The

The standard switches have one, three, and five switch-

silver-to-silver contacts of the JA switch consist of

ing decks, which are indicated in the type designation

pure silver welded to beryllium copper. Silver or

by the number following JF.

silver-coated contacts are now being used for the latest

The original production of the switches had a detent

type JA switches and other low-current switches. In

to limit the switching action to two positions. The

larger switches, silver (unless alloyed with other

present design has a 12-position detent arrangement

metals) is unsatisfactory because it vaporizes too

with adjustable stops. The stops can be adjusted

readily due to arcing.

by removing the four screws on the back plate and

The JA switch is available in two, six, and ten

arranging the stop arms mounted on the switch shaft to

sections. An example of the switch designation is

give the number of positions desired.

JA6C( 16) for a 6-section, 16-position switch; here the

An O-ring on the switch shaft within the mounting

first number designates the number of sections, the C

bushing prevents water from entering the switch. An

indicates common rotor, and the number in

O-ring is also provided on the outside of the mounting

parentheses indicates the number of positions.

bushing to give a watertight seal against the panel

in which the switch is mounted. These features have

TYPE JF.-- The JF switch (fig. 2-12) was

eliminated the need for a watertight cover over the

developed primarily to replace toggle switches in the

switch.

10- and 20-switch boxes for sound-powered telephone

The JF switch is satisfactory for 120-volt ac

applications.

applications up to 1 ampere. It is being used in sound-

Because of the problems in making toggle

powered telephones, loudspeakers, microphone sta-

switches watertight, it was necessary to provide a

tions, and similar low-current equipment.

cover with a gasket for the 10- and 20-switch boxes,

which contained the toggle switches. The cover had to

CAUTION

be open when the switches were operated. Therefore,

the switch box was not watertight, leading to possible

The switch decks are made of molded

malfunctioning of the switches. In addition, the lack

nylon material. Be careful in soldering the leads

of a strong contact wipe action in toggle switches and

to the switch contacts. Too much heat passing

the low voltage and current in sound-powered circuits

back to the switch deck will destroy the switch

resulted in the formation of an insulating film on the

deck or damage the insulation between

contacts. This film resulted in open circuits or, if

adjacent contacts.

required, several operations of the toggle switch

handle before the circuit was initially made.

The JF switch replacement uses silver-to-silver

contact surfaces and provides a strong wiping action in

Figure 2-11.--Type JA switch.

Figure 2-12.--Type JF switch.

2-7