Westinghouse Prototype 15 inch Color Set

This set was apparently a prototype for the H840CK15. There are several differences from the production set. The mask around the picture tube is yellow, rather than white as in the production set. Different style tuners are used, and a different arrangement is used to hold the yoke assembly to the chassis.

On the left is the prototype high voltage cage. A single 1B3 is used as rectifier, while 3 - 3A3s are used as a voltage doubler in the production model. The chassis is marked, in pencil, "Needs to be modified - 1B3"

On the left is the color processing chassis from the prototype. Notice that it doesn't have the hue control brought out to the rear as on the production set.

The prototype has an extra chassis connected between the video and color processing circuits. It has a 12AU7 and a 6AL5. We have traced the circuit, and it attaches to the hue coil. A difference voltage is derived from across the coil, which then adjusts the color balance and level. It was an attempt to eliminate the hue control and keep the color level stable so that the color intensity control didn't need to be constantly adjusted. Apparently it didn't work well, or was too expensive to include in the production set.

The prototype is stamped PP6 (perhaps for production prototype #6), while the production model has a serial number.