Sylvania 8XP4 Television Picture Tube (1950s)

              

This 8XP4 television picture tube is designed specifically for test purposes. I bought it when restoring my DuMont RA-113 to substitute for its 17-inch 17AP4 CRT.

The RA-113's own picture tube is bulky and I had no practical way to fit it onto my workbench with the large chassis and yoke. It was impossible to power up the TV and view its screen on the workbench.

The solution is this handy little test tube, created by Sylvania for exactly this situation. Here's the 8XP4 with its original box, four cables, and a removable plastic mask that fits over the tube's face:

The mask provides a simple template for making adjustments such as height, width, and centering.

This sheet, included with the tube, describes its features and applications:

  

The 8XP4 is designed to substitute for tubes with a 90° deflection angle. It is rectangular, like the tubes it can replace. Sylvania made a similar, round testing tube, the 5XP4, which subs for tubes with a 53° or 70° deflection angle.

As noted in the sheet, the 8XP4 is self-focusing, so you don't need to place the TV's focus coil around its neck. Of course, you do have to put on the TV's deflection yoke, to make the picture fill the screen vertically and horizontally.

These tubes were often packaged in a handy case which a repairman could carry along when making a field call at a customer's house. The case with tube and accessories was sold by Tele-Check (and perhaps other companies), so if you're looking for one of these, search for that name as well as 8XP4.

Here is the Sylvania 8XP4 data sheet, which gives technical details:

The next photo shows the 8XP4 in action, sitting next to my DuMont RA-113 chassis on the workbench.

You can read more about that application in my DuMont RA-113 article.

A test tube like this isn't absolutely necessary. I restored more than two dozen TVs before I finally decided that I wanted one. If you happen to find one, however, it can simplify your project, as it did the work of TV repairmen back in the day.

I also own a 5AXP4 CRT, a 5-inch tube that substitutes for earlier round picture tubes. It came as part of a Tele-Check kit with carrying box and accessory cables.

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