g. A d j u s t t h e S C R E E N f i n e c o n t r o l u n t i l t h e S C R E E N V O L T S
m e t e r indicates the voltage specified on the tube test data roll chart
(par. 12).
h. Set the BIAS fine control to its extreme clockwise (maxi-
mum) position.
i. W i t h t h e P R E S S T O T E S T P 5 s w i t c h h e l d i n i t s o p e r a t e d
p o s i t i o n , gradually reduce the bias voltage by adjusting the BIAS
fine control until the tube strikes its firing potential. The firing
p o t e n t i a l is indicated by a sudden increase in load current shown
o n the PLATE meter and by a sudden decrease on the PERCENT
QUALITY meter.
Note. The tube will not conduct (as indicated by an increase in load current
shown by the PLATE meter) until the critical grid-bias voltage is reached.
For example, for a type 2D21W or type 2050W tube, the bias voltage at which
conduction occurs should be between 1.5 and 3.0 volts.
j. T h e v o l t a g e a t w h i c h t h e t u b e s t r i k e s i s r e a d o n t h e G R I D
BIAS VOLTS meter. Record the grid voltage at the instant and
a t the point that the pointer starts to deflect. This is the striking
v o l t a g e of the tube under test. Repeat the test to confirm the read-
ing. Minimum limits for striking voltages of thyratrons are given
o n the tube test data roll chart.
k. W h e n t h e t e s t i s c o m p l e t e d , s e t t h e O N - O F F p o w e r s w i t c h
to the OFF position, remove the tube under test from the test
socket, and return all switches and controls to their safety posi-
tions (par. 15d).
There are two types of electron-ray (ER) indicator tubes that
can be tested with the TV2(*)/U, Type 6U5 and similar tubes
have a triode section and a single indicator (one shadow). Type
6AF6 and similar tubes have no triode section, but have twin
indicators (dual shadow). Follow the procedure below to check
the opening and closing action of the eyes only. Indicators with
t r i o d e s e c t i o n s a l s o m u s t b e t e s t e d f o r e m i s s i o n (i b e l o w ) .
a. P e r f o r m t h e o p e r a t i o n s i n d i c a t e d i n p a r a g r a p h s 1 5 a n d 1 6 .
b. O p e r a t e t h e F U N C T I O N s w i t c h t o t h e T E S T p o s i t i o n .
c, O p e r a t e t h e P L A T E - S C R E E N R A N G E s w i t c h t o t h e p o s i -
t i o n specified on the tube test data roll chart.
d. A d j u s t t h e P L A T E a n d S C R E E N f i n e c o n t r o l s u n t i l t h e
exact voltages specified on the tube test data roll chart are indi-
cated on the corresponding meters.
e. D e p r e s s t h e P R E S S T O T E S T P 4 s w i t c h . I f t h e t u b e i s a
single indicator, the indicator should be closed; if the tube is a
twin-indicator tube, such as the 6AD6 or 6AF6, indicator No. 1
s h o u l d be closed and indicator No. 2 should be open.
