Sylvania 5AXP4 Test Picture Tube (1950s)
The 5AXP4 picture tube was designed for TV repairs. Small, rugged,
and versatile, it can substitute for many larger picture tubes, saving time
and aggravation in the workshop.
These special test CRTs were sold alone or as part of a kit like the 5AXP4
The box contains the picture tube, accessory cables, and yoke:
Using the 5AXP4 Picture Tube
You can use the substitute picture tube in or out of the box. In this photo, I left it
in the box and used extension cables to connect to my
Philco 49-1240 TV chassis on the workbench.
In that photo the 5AXP4 box is sitting to the left of my oscilloscope,
allowing me to view the screen image while making horizontal adjustments
with the aid of the scope.
It's a great convenience to leave the TV's big picture tube in
the cabinet for such work. Often, as with my
Philco 49-1240 and
RCA 630TS, the CRT is supported
by the cabinet and there's no easy way to secure it when
you put the chassis on the workbench.
If you don't have a little sub CRT like this, you have two choices
for operating such a TV on the workbench. You can prop the CRT
on the bench with pieces of wood, styrofoam, or whatever, and hope
that you don't knock it over or break the neck. Or, you can
reinstall the chassis into the cabinet every time you want to
play the TV and view the screen image. Using this 5AXP4 is
both quicker and easier: simply plug it in and play.
In the next photo, I removed the 5AXP4 tube from the box and inserted
it in the yoke of my
RCA 721TCS chassis:
When using the 5AXP4 CRT alone, as in the previous photo, no extension cables are needed.
As you can see in the data sheet,
the 5AXP4 is a round 5-inch CRT with 53-degree deflection angle, allowing it to
substitute for many early television CRTs, such as the 10BP4 or 12LP4. It is self-focusing and it
requires no ion trap magnet.
When using the test CRT with its own, generic yoke, the geometry of the screen
image may not be exactly the same as if you were using the TV's big CRT. For instance, if
you look back at the photo of the Philco 49-1240 chassis on the workbench, the crosshatch
test image is taller and narrower than usual.
The difference wasn't important in that case,
since I only wanted to see whether the image was stable and observe the pattern while making adjustments.
Naturally, you'll want to put the chassis back in the cabinet and connect the TV's own
CRT to make the final screen adjustments for screen width, height, and so forth.
The 8XP4 Picture Tube
For later TVs using a rectangular picture tube, there is a similar test CRT, type
I also own one of those, shown here connected to my DuMont RA-113 and with its
For more details, go to the 8XP4 link above.
These test CRTs are readily available in the used market, often for less than $50.
Expect to pay a little more a complete kit including box, yoke, and accessory cables.
The kits were sold under various names, including Tele-Check.