[M3-SRT8]

Originally Posted by John Folsom

There were several late 1940s TVs which featured some form of magnification or zoom. Most designs simply increased the vertical height, as discussed earlier in this thread.

But Westinghouse took the concept to its logical extreme in the Model H-605T12. This 12 inch table set has a front panel control labeled electronic magnification. When in the normal position, the CRT was masked off in the conventional "double D" format; that is a round CRT with the top and bottom masked off and the sides left rounded, to approximate the 4:3 aspect ration of the trnasmitted image. When the control was moved to the magnification position, two things happened. First, two mechanical shutters at the top and bottom of the CRT moved outware to reveal the full round CRT. Second, both the vertical sweep height and horizontal sweep width were increased to completely fill the round CRT, while maintaining the 4:3 aspect ration of the inage. The magnification was accomplished by switching in two separate vertical height controls to set the vertical height, and the B+ voltage to the horizontal output stage was switched between 2 values to cause the width to change.

In a conventional flyback type horizontal deflection system, changing the B+ voltage would have drematic effects on the high voltage as well as the width. Westinghouse avoided this complication by implementing a RF type high voltage power supply, which operates independently of the horizontal deflection circuitry. This HV supply is a souped-up version of the RF high voltage supply commonly used in 7" sets of the period. It was relatively uncommon to use RF high voltage supplies in sets employing CRTs bigger than 7 inches. The horizontal deflection circuitry of this set used 3 7A3's in parallel to drive a conventional transformer coupled deflection yoke. This set can be found in Sams #97-19.

A friend of mine has one of them, and, I'm trying to persuade him to part with it. Does yours work? Any unusual difficulties in restoring it?

LJB