Line Voltage Test Circuit

are connected in parallel with copper oxide rec-

(4) Secondary No. 3 (A, fig. 3) Supplies

tifier CR101 and bridge-balancing resistors

a 5-volt ac signal voltage for mutual

R123 and R125 (and meter shunt resistors

conductance tests. A voltage divider

R131 and R132, when used, on the TV-7A/U).

network consisting of R120, R121, and

At the same time, the rectifier bridge circuit is

R122 (fig. 42-44), connected across

connected between terminals 19 and 37 of T101

this winding, also provides signal volt-

through voltage-dropping resistor R124 and

ages of 1 volt and 0.5 volt, depending

variable resistor R134 (TV-7 B/U and TV-

on the resistor or resistors used.

7D/U only).

d. Filament Supply. Secondary No. 7 of

T101 (A, fig. 3) supplies filament voltage to the

(1) O n the TV-7/U and TV-7A/U, the

tube under test and voltage for rectifier emis-

v a l u e of voltage-dropping resistor

sion tests. Terminals 19 through 37 provide

R124 is such that, when 121 volts ac

voltages from 0 volt to 117 volts, under load.

(no load) exists between terminals

No-load voltages will be slightly higher. As an

19 and 37 of transformer T101, and

example, the no-load voltage measured between

pushbutton 1 -- L I N E ADJ. is de-

terminals 19 and 37 will be approximately 121

pressed, the meter pointer will indi-

volts with 93 volts across the primary. FILA-

cate at LINE TEST.

M E N T VOLTAGE switch S108 is used to

(2) On the TV-7B/U and TV-7D/U, the

select the desired filament voltage for the tube

value of resistors R124 and R134 are

under test. The BLST. position of switch S108

such that, when 121 volts ac (no load)

enables ballast tubes to be tested for continuity,

exists between terminals 19 and 37

and supplies voltage to certain rectifier tubes

of T101 and variable resistor R134 is

for emission tests. Center-tapped resistor R110

properly adjusted, the meter pointer

prevents injection of the filament voltage into

w i l l indicate at LINE TEST when

the grid signal voltage.

pushbutton 1 -- LINE ADJ. is de-

pressed.

7. Line Voltage Test Circuit

c. When power is applied to the test set and

(fig. 3 and 42-44)

the setting of resistor R126 is varied, the volt-

The line voltage test circuit consists prima-

age across the primary and the secondaries of

rily of a bridge circuit connected parallel to

T101 will change. The meter pointer should in-

terminals 19 and 37 of transformer T101. Meter

dicate at LINE TEST when pushbutton 1 --

M101, which can be switched into the bridge

LINE ADJ. is depressed and resistor R126 is

circuit, provides an indication of the proper ad-

properly adjusted.

justments of LINE ADJUST control R126.

d. Current flow through the line voltage test

a. The ac voltage between terminals 19 and

circuit is as follows:

37 of T101 is applied to the rectifier bridge cir-

cuit through part of switch S1101 and re-

(1) When terminal 37 of T101 is negative

sistors R134 (TV-7B/U and TV-7D/U only)

with respect to terminal 19, the right-

and R124. The rectifier bridge circuit, except

hand part of CR101 will conduct and

for the TV-7A/U, consists of copper oxide

the left-hand part of CR101 will not

rectifier CR101 and bridge-balancing resistors

conduct. Current will flow from termi-

R123 and R125. On the TV-7A/U (fig. 42 and

nal 37 through one part of switch

43), in addition to bridge-balancing resistors

S110-1, variable resistor R134 (TV-

R123 and R125, when meter shunt resistors

7B/U and TV-7D/U only), and volt-

R131 and R132 are used they are also part of

age-dropping resistor R124 to the

the rectifier bridge circuit and are connected in

junction of R123 and R125. The cur-

rent will divide at this point. Some of

parallel with copper oxide rectifier CR101. Re-

sistors R131 and R132 are added to the bridge

the current will flow through R125;

circuit, as required, during initial calibration

the remainder of the current will flow

of the line adjust circuit.

through R123, part of switch S110-1,

b. When pushbutton 1 -- LINE ADJ. is de-

meter M101 and filter capacitor C103,

pressed, meter M101 and filter capacitor C103

and another part of switch S110-1.