Gas Test Circuit

c. For diodes, depressing PRESS TO TEST

grids are connected to the plate while the sup-

P2 switch S17 applies voltage to the tube under

pressor grid is tied to the cathode; the tube them

test and emission current is read in percent

functions as a diode. When PRESS TO TEST

P3 switch S18 is depressed at the same time as

quality of the rated value on PERCENT QUAL-

ITY meter M3.

P2 switch S17, emission current is read in per-

cent quality of the rated value on PERCENT

d. For multigrid tubes, the control and screen

QUALITY meter M3.

NOTE:

ON TV-2C/U, R24 AND R25 ARE

CONNECTED DIFFERENTLY. REFER

TO SCHEMATIC DIAGRAM.

TM6625-316-35-6

Emission measurement circuit of Test Set, Electron Tube TV-2(*)/U,

Figure 6.

Simplified Schematic diagram.

which depends on the plate and grid voltages

7. Gas Test Circuit

set up for the transconductance test of the tube

(figs. 7 and 26)

(par. 5). Depress PRESS TO TEST P6 switch

a. A gas test performed' on an amplifier-type

S21 to insert resistor R58 into the grid circuit of

tube will detect an excessive amount of gas in

the tube under test. If the tube is gassy, the

the tube. A gassy tube will not function cor-

source of grid-bias voltage C will cause current

rectly. Ionization of residual gas in a tube causes

to flow through the grid circuit in the direction

grid current to flow, and thus changes the grid-

indicated by the arrows (fig. 7). The gas cur-

bias voltage and other operating characteristics

rent develops a voltage drop across resistor

of a tube.

R58, which tends to place the grid end of the

resistor at a positive potential and reduce the

negative grid bias; an increase in plate current

b. The gas test circuit of Test Set, Electron

results. This increase in plate current is indi-

Tube TV2(*)/U is part of the transconduct-

cated on PERCENT QUALITY meter M3. The

ance test circuit (par. 5) only parts involving

pointer of meter M3 will move less than three-

the grid circuit are shown in the simplified

scale divisions if the tube under test has a negli-

schematic diagram (fig. 7). Plate current

gible gas content.

through the tube under test has a certain value,

AGO 1428A