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Early Electronic Television

Purdue University Experimental Set

 

This set was built by the Electric Engineering department at Purdue University. It was made in 1932 for reception of 60 line mechanical transmissions from the University's station W9XG. The Purdue engineers were probably the first to add synchronizing pulses to their transmissions, short ones at the beginning of each line, and long ones at the start of each frame. These pulses were added to the video information at a signal level higher than the level of black (called "blacker than black"), and could be extracted by the electronic receiver. The 1932 Purdue set is among the first electronic TV receivers.

The book A Century of Progress: The History of Electrical Engineering at Purdue (1888-1988) has a chapter about television. Here is a description of the set:

In 1929, the Grigsby-Grunow (Majestic) Radio Company desired to advance television, which, although mechanically based, was attracting much attention. On May 7 of that year, Roscoe George and his colleague, Howard J. Heim, entered into a contract to develop an improved all-electronic television receiver.

While others, notably Zworykin and Farnsworth in the United States, tacked the problem of making an all-electronic camera, George and Heim began the task of eliminating the rotating disk in the receiver by creating the first all-electronic television receiver.

George and Heim added a second (vertical) sweep circuit to George's newly developed cathode-ray oscilloscope to permit display of television images. They created a linear sweep by charging a capacitor through a pentode (57), which operated as a constant current device. A thyratron (885) was used to discharge the capacitor to return the sweep to its starting point. They solved the synchronizing problem by cutting a notch in the spinning disk camera so that a pulse was obtained for each revolution of the scanning disk.  

Roscoe George, who built the set, in a picture taken in the early 30s.