<s>
The	O
7JP4	B-General_Concept
is	O
an	O
early	O
black	O
and	O
white	O
or	O
monochrome	O
cathode	B-Device
ray	I-Device
tube	I-Device
(	O
also	O
called	O
picture	B-Device
tube	I-Device
and	O
kinescope	O
)	O
.	O
</s>
<s>
The	O
7JP4	B-General_Concept
has	O
a	O
7	O
"	O
diameter	O
round	O
screen	O
which	O
was	O
often	O
partially	O
masked	O
.	O
</s>
<s>
Unlike	O
later	O
electromagnetically	O
deflected	O
TV	O
tubes	O
,	O
the	O
7JP4	B-General_Concept
is	O
electrostatically	O
deflected	O
like	O
an	O
oscilloscope	O
tube	O
.	O
</s>
<s>
The	O
7JP4	B-General_Concept
is	O
part	O
of	O
the	O
7JPx	O
series	O
of	O
circular	O
face	O
electrostatic	B-Device
cathode	I-Device
ray	I-Device
tubes	I-Device
(	O
CRT	O
)	O
.	O
</s>
<s>
Originally	O
developed	O
for	O
radar	O
applications	O
as	O
a	O
display	O
device	O
for	O
radar	B-Algorithm
display	I-Algorithm
A	I-Algorithm
scopes	I-Algorithm
around	O
1944	O
.	O
</s>
<s>
The	O
7JP4	B-General_Concept
(	O
P4	O
represents	O
the	O
phosphor	O
that	O
glows	O
white	O
and	O
has	O
medium	O
persistence	O
)	O
for	O
television	O
.	O
</s>
<s>
The	O
screen	O
diagonal	O
is	O
7	O
inches	O
(	O
17.8cm	O
)	O
for	O
7JP1	O
and	O
7JP4	B-General_Concept
,	O
but	O
only	O
5.5	O
inches	O
(	O
14cm	O
)	O
for	O
the	O
7JP7	O
.	O
</s>
<s>
From	O
1946	O
to	O
1951	O
the	O
7JP4	B-General_Concept
was	O
a	O
common	O
CRT	O
(	O
Picture	B-Device
Tube	I-Device
or	O
Kinescope	O
)	O
used	O
in	O
lower	O
priced	O
televisions	O
sold	O
in	O
the	O
United	O
States	O
.	O
</s>
<s>
Horizontal	O
and	O
vertical	O
electromagnets	O
are	O
placed	O
at	O
the	O
picture	B-Device
tube	I-Device
neck	O
,	O
called	O
the	O
"	O
yoke	O
"	O
.	O
</s>
<s>
The	O
first	O
heavily	O
mass-produced	O
large	O
picture	B-Device
tube	I-Device
to	O
use	O
this	O
newer	O
method	O
of	O
deflection	O
was	O
RCA	O
's	O
10BP4	O
,	O
introduced	O
in	O
1946	O
.	O
</s>
<s>
Soon	O
after	O
electrostatic	O
picture	B-Device
tubes	I-Device
and	O
the	O
television	O
electronic	O
design	O
would	O
be	O
completely	O
replaced	O
.	O
</s>
<s>
For	O
a	O
detailed	O
look	O
at	O
US	O
electrostatic	O
TV	O
design	O
and	O
the	O
7JP4	B-General_Concept
Kinescope	O
from	O
an	O
Australian	O
view	O
(	O
by	O
)	O
go	O
to	O
the	O
external	O
link	O
below	O
involving	O
the	O
Wards	O
Airline	O
TV	O
(	O
Sentinel	O
model	O
400TV	O
)	O
.	O
</s>
<s>
The	O
restoration	O
of	O
early	O
US	O
made	O
television	O
sets	O
has	O
spurred	O
interest	O
in	O
the	O
7JP4	B-General_Concept
.	O
</s>
<s>
Because	O
it	O
is	O
electrostatically	O
deflected	O
and	O
was	O
obsolete	O
by	O
the	O
mid-1950s	O
,	O
most	O
CRT	O
testers	O
will	O
not	O
test	O
the	O
7JP4	B-General_Concept
and	O
thus	O
it	O
is	O
best	O
tested	O
in	O
a	O
working	O
TV	O
set	O
.	O
</s>
<s>
The	O
Precision	O
CR30	O
,	O
Sencore	O
CR-70	O
and	O
Jackson	O
707	O
are	O
some	O
of	O
the	O
CRT	O
testers	O
that	O
are	O
capable	O
of	O
testing	O
the	O
7JP4	B-General_Concept
,	O
3KP4	O
and	O
other	O
electrostatic	O
deflection	O
CRTs	O
.	O
</s>
<s>
There	O
are	O
many	O
picture	B-Device
tube	I-Device
restoring	O
equipment	O
available	O
for	O
magnetic	O
deflection	O
tubes	O
but	O
there	O
is	O
no	O
way	O
to	O
restore	O
electrostatic	O
tubes	O
.	O
</s>
<s>
The	O
biggest	O
problem	O
with	O
many	O
picture	B-Device
tubes	I-Device
is	O
the	O
loss	O
of	O
emission	O
or	O
electron	O
production	O
due	O
to	O
contaminated	O
or	O
damaged	O
cathode	O
that	O
surrounds	O
the	O
heater	O
.	O
</s>
