Rectifier Test Circuit

b. Noise Test Circuit. The shorts test Cir-

SWITCH is turned from positions 1

cuit is also used when testing a tube for noise.

through 5. A short between two or

NOISE test jacks J103 and J104 are used to

more elements of the tube under test

connect a radio receiver or an audio amplifier

will complete the circuit between C102

(para 22, TM 11-6625-274-12) in parallel with

and R109, C105, and the neon

SHORTS lamp E101 through isolating capaci-

SHORTS lamp. The voltage applied

tor C101. Intermittent disturbances between

to the SHORTS lamp will cause the

the tube elements can often be made to occur by

gas to ionize, thereby producing a

tapping a tube. Momentary shorts, which are

visual indication of an interelement

too brief to be indicated by the SHORTS lamp,

short.

permit the alternating voltage across R107 to

(3) If the polarity of the applied voltage

be applied to the neon lamp and cause a brief

is such that terminal 13 of T101 is

oscillation. The oscillations are reproduced and

negative with respect to terminal 11,

amplified by the radio receiver or the audit! am-

and a short exists between two ele-

plifier and are heard as an audible signal simi

ments of the tube under test, the cur-

lar to static.

rent flow will be as follows:

(a) The total current in the circuit will

9. Rectifier Test Circuit

f l o w from terminal 13 of T101

(fig. 8, 9, and 42-44)

through R108 to the junction of

The rectifier test circuits in the TV-7(*)/U

C102 and R107. The current will

are similar to the simplified rectifier test cir-

divide at this point. Some of the

cuit shown in figure 9.

current will flow through R107 to

a. The circuit shown in figures 8 and 9 is

terminal 11 of the transformer; the

used when the rectifier tube under test is

remainder of the current will flow

supplied with a test voltage of 35 volts ac.

through C102 and across the short

(1) Some diode tubes, such as the 6H6,

within the tube under test to the

use a test voltage of only 20 volts ac,

o f C 1 0 5 , R 1 0 9 , and

junction

which is supplied by part of secondary

SHORTS lamp E101. The reactance

No. 2 of T101 (fig. 42-44). The actual

of C105 and the resistance of R109

voltage applied between the plate and

are v e r y h i g h c o m p a r e d w i t h

the cathode is approximately 18 volts

the resistance of the conducting

ac because of a voltage drop across

SHORTS lamp. The majority of the

current limiting resistor R117.

current, therefore, will flow through

(2) A test voltage of approximately 287

the SHORTS lamp to terminal 11

volts ac is applied to rectifier tubes of

of T101.

the cold cathode type, such as the OZ4.

(3) Because of the different voltages re-

(b) When terminal 11 of T101 is nega-

quired to test various types of diodes,

tive with respect to terminal 13,

the test circuits will necessarily be

current will flow to the junction of

s l i g h t l y different from the circuit

resistors R107 and R109, capacitor

shown in figures 8 and 9.

C105, and SHORTS lamp E101.

b. Filament voltage is supplied to the recti-

S o m e of the current will flow

fier tube under test (fig. 8 and 9) from ter-

through R107 to the junction of

minals 19 and 27 of transformer T101. When

R108 and C102; the majority of the

pushbutton switch S110-7 is depressed, 35 volts

remaining current will flow through

ac is applied between the cathode and the plate

t h e SHORTS lamp, across the

of the tube under test. The tube will conduct

shorted elements within the tube

only when the plate is positive with respect to

under test, and through C102 to

the cathode, thereby producing a pulsating dc

the junction of resistors R107 and

flow through the circuit. The current through

R108. The total current in the cir-

meter M101 is proportional to the electron

c u i t will flow through R108 to

emission of the tube, and the amount of deflec-

terminal 13 of T101.