Television Test Device
This device was sold by Philips around 1950. It is used to align the optical focus of their Protelgram projection units. It is the same size as the 3NP4 CRT. The test device is installed in place of the CRT, and 6 volts AC is applied to the pins on the bottom. The test pattern on the device is projected to the screen, where it can be viewed in a dark room. The image is then focused using the mechanical adjustments on the Protelgram assembly. Then, the test device is removed, the CRT installed, and the electrical focus is adjusted for the sharpest picture. RCA also sold a similar device for its projection sets. Thanks to Chuck Azzalina and Tim Mullen for this information.