e. Measurement of Transconductance. To test the transcon-
ductance of the triode section of the 6SQ7 tube, proceed as outlined
below. The FUNCTION switch and all SELECTORS switches
are set as in a (2) through (7) above.
(1) Set the PLATE-SCREEN RANGE switch to the J posi-
tion.
(2) Adjust the PLATE fine control until the PLATE meter
i n d i c a t e s 225 volts.
( 3 ) Set the BIAS RANGE switch to the 5 position.
(4) Adjust the BIAS fine control until the GRID BIAS
V O L T S meter indicates 2 volts.
( 5 ) Turn the SHUNT control to 90.
(6) Adjust the PERCENT QUALITY meter to zero (par.
( 7 ) Set the GM-SIGNAL RANGE switch to D.
(8) Adjust the SIGNAL-V.R. control until the SIGNAL
meter pointer is on the red line.
(9) Depress the PRESS TO TEST P2 switch to its locking
position. Read the percent quality of the 6SQ7 tube on
the PERCENT QUALITY meter. If the reading is below
t h e minimum limit of 25, discard the tube; if it borders
on 25, the tube may be used but should be replaced soon.
If the meter pointer is beyond full scale, test the tube
for gas.
f. Test for Excessive Gas. To test the tube for gas, proceed as
outlined below. The FUNCTION switch and all SELECTORS
s w i t c h e s and range switches are set as in e above, and the FILA-
M E N T VOLTS meter indicates 6.3 volts.
(1) Depress the PRESS TO TEST P2 switch to its locking
position.
( 2 ) Depress and hold down the PRESS TO TEST P6 switch.
If the pointer of the PERCENT QUALITY meter re-
m a i n s at 25 or near 25, the tube does not contain exces-
sive gas. If the pointer moves more than three scale
divisions in either direction, however, the tube contains
too much gas for satisfactory operation.
e m i s s i o n of diode No. 1, adjust the tube test data roll chart so the
s e c o n d line on which the 6SQ7 tube appears is between the hori-
zontal red lines. The FUNCTION switch, all SELECTORS
switches except the PLATE switch, and the PLATE-SCREEN
35
