April 2004 update: Four Model 5 sets survive. The first is in the care of Ed Reitan and may be an engineering unit that predates the Model 5’s modest run of a couple hundred. The second Model 5 (B583) was acquired in late 2003 by the Early Television Foundation near Columbus, Ohio and is restored to full operation. The Third Model 5, serial number B668 and discovered in New Jersey in 2000, is now in Connecticut. At the Early Television Convention in April 2004, John sold B570 to Florida collector, Wayne Abare.
November 30, 2004 update: Wayne writes, "I have just finished making cabinet repairs. John Folsom helped me put the CRT back into the set yesterday. John noticed the number 14 stamped into the upper right back side of the cabinet frame. Here is more information on this set.
The label on the Prototype 15GP22:
DEVELOPMENTAL TYPE C-73599
SERIAL NO. 5390
This tube is supplied for laboratory and experimental purposes only, with no obligations as to its future manufacture, unless otherwise arranged.
RADIO CORPORATION of AMERICA
RCA VICTOR DIVISION
Four of the 6AN8 tubes had a label stating:
"This tube is for experimental purposes only, without obligations as to its future manufacture, unless prearranged. 9438
RADIO CORPORATION of AMERICA
Tube Department Harrison, NJ"
According to a vintage ad by the Harrison tube department, the 6AN8 was developed specifically for color television. When the CT-100 run was started a few months later, production 6AN8s were used. --Pete
These four represent two-percent of all the Model 5's believed built for the January 1, 1954 coast-to-coast color network broadcast of the Rose Bowl Parade. Curiously, it is about the same percentage as the number of surviving CT-100’s now documented.
Of course, there may be others under wraps somewhere, waiting to be discovered just as this one was in the summer of 2003, but it is one of only four KNOWN surviving sets. The Model 5 contains a slightly different tube complement: the I and Q demodulators are different (5915), for example. And the first three video IF stages are 6CB6 rather than the 6DC6 used by the production CT-100. In John's set, the 5915's were long ago replaced with the same demodulators used in a CT-100, the pin-for-pin replacement 6BY6.
Model fives were never sold to the public.
Model 5 Chassis : S/N B570
This set was built in late 1953. There is strong evidence that late in 1954 this set was upgraded with new tubes in critical functions such as inside the high-voltage cage shown here. (John never opened the cage; therefore, it has been sealed for a minimum of 25 years and very possibly since late 1954, a total of 49 years. Not exactly King Tut stuff, but I enjoyed the moment.)
This leads to speculation that the picture tube was replaced at that time also, and that the set was used in some technical function, either at NBC in Manhattan or other location. There is an auxiliary circuit that was added to the chassis. An SO-239 coax connector connects to a single, triode-connected 6J6 added to the chassis. The connector is wired through a large electrolytic to the cathode of the 6J6, which means the stage could just as well have been an output as an input.
Upon initial investigation, the 6J6 no longer appears be connected to the original circuitry. But this auxiliary circuit was placed in the chroma circuitry area, adding fuel to the possibility that this set was once used to drive instrumentation.
Insert shows spring-tethered 6BD4 plate cap.
A second and final tidbit concerns the design of internal cage wiring. This set uses a spring instead of insulated wire to make the connection to the plate cap of the 6BD4 high-voltage regulator.