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The Set: Pete Deksnis's Site about the CT-100

Restoring a Vintage Color Television Set

A One-Degree-of-Separation Tale from the Days of Color Television Development.

 

Who Is Robert B. Dome and What Is He Doing Here?

by Pete Deksnis

 

O

ne day in 1955 I visited my father’s office in downtown Philadelphia and saw his brand new Granco Model 610 FM tabletop receiver. Its modest 4-by-6-in. speaker made very impressive music for such a small radio. Apparently, that erstwhile New York manufacturer of low-cost FM receivers did more to popularize FM back then than Fisher or Zenith or RCA.

 

I learned much later that one reason my father’s Granco 610 sounded so good was because of negative feedback. Granco engineers were always looking for ways to skimp and save to hold costs down yet still give the customer value and performance. One ingredient was negative feedback where you feed 180-degree out-of-phase audio from the output transformer secondary to the voltage amplifier driving the audio power stage. It lowers the gain of the audio circuitry, but it improves the response and lowers distortion too. A nice compromise; everybody wins.

 

Five years before my first look at the Granco 610, the General Electric Company was hard at work developing color television, as were RCA, Philco, CBS, Hazelton, and others.

 

By July 1950, GE had developed a way to squeeze color information needed by a set into the same channel that carried the black and white TV signal. Philco devised a way to modulate two separate chrome signals on the same carrier using quadrature modulation by early 1951. But it was GE who showed how to slip Philco’s quadrature signal into the existing NTSC black and white signal.

 

GE described how luminance sidebands occur in bunches, with basically empty space between each bunch, and so Philco’s quadrature chroma signal, which also occurs in bunches, could be placed between the luminance bunches. This GE-developed technique, known as frequency interlace, and the Philco-developed quadrature modulation technique, squeezed all the information needed for brilliant NTSC color into the existing NTSC black and white signal.

 

In July 1950, Dr. W.R.G. Baker, GE vice president and general manager of the electronics department, released information about its new frequency interlace technique for compatible color television.

 

U.S. patent 2,302,493 granted in 1942 was for an audio amplifier design that used negative feedback from the output transformer secondary to the voltage amplifier driving the audio power stage. It’s what Granco did to boost the audio quality of my father’s 610.

 

The name on the patent for audio amplifiers with negative feedback and the name of the person given credit by GE for the frequency interlace technique are the same: Robert B. Dome.

 

[July 8, 2007]