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 Tele-Check:

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 8XP4. I also own one of those, shown here connected to my DuMont RA-113 and with its accessory cables.


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.

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