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21-CT-55 Color Receiver (CTC2B Chassis, 1954)

(Red Mahogany or Blonde grained finish, retail: $895)

V1.00 03-14-1999

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21-CT-55 CTC2B Service Manual Color Line

RCA Victor started production of the 21-CT-55 on December 1, 1954. RCA released the 21CT55's service literature, "1954 No. T13", on November 24, 1954. RCA also published a Television Service Clinic booklet, "Technical Features of the RCA Victor Model 21CT55 Color Television Receiver". To quote from it:

"The RCA Victor Model 21CT55 color television receiver is a direct-view console which reproduces high-quality television pictures in full color from a standard color television signal, and automatically, with no adjustment or attachments, high-definition black-and-white television pictures from a standard black-and-white television signal.

The picture displayed on the screen of a 21-inch tricolor kinescope, the 21AXP22, has an area of approximately 255 square inches (2 1/2 times the CT-100). The 21AXP22 employs electrostatic focusing and electromagnetic convergence. Ultor voltage is 25,000 volts. In conjunction with the 21-inch tricolor kinescope, the convergence and purity arrangements provide ease of adjustment, and increased accuracy and stability of color registration.

One of the customer convenience features in this receiver is that convergence and focus are no longer customer adjustments from the side of the cabinet but are internal and are preset by the service technician.

Additional features include: a removable top panel to facilitate servicing and adjustment, and the location of most of the functional controls at the receiver front. These control are located under the tilt-down control cover or behind the removable wood panel directly below the control cover. Dual loudspeakers are provided for sound reproduction."


Shortly after the introduction of the 15-inch CT-100, RCA announced that they would develop a 19-inch color CRT using a similar planar shadow mask and flat phosphor screen with decorative mask suspended inside a round glass envelope. RCA disclosed and showed a "19-inch CT-100" (photos will be in the book). In June of 1954, CBS Hytron announced its 19-inch "205" (sq. in.) color crt, with its curved shadow mask and color phosphor dots deposited inside the curved face plate,. The success of the CBS Hytron "Chromatron" in models by Motorola and CBS-Columbia, led to the abandonment by RCA of its 19-inch tube. RCA then put all emphasis into developing a similar curved shadow mask and faceplate. The experimental C-73685 21-inch tube was described in September, 1954. It featured a new Magnetic Field Equalizer Assembly, with 8-adjustable magnets positioned around the faceplate of the kinescope. With its 70-degree deflection angle the CRT was 25 5/16-inches long. The eventual production 21CT55's 21AXP22 color kinescope used wide gamut phosphors and provided a rounded side 19 5/16-inch wide by 15 1/4-inch high picture.

The 21CT55 featured the same high-quality signal processing circuit as the CT-100 - tuner, I.F. strip, and color processing was identical. One odd variation was that the 21CT55 demodulated along R-Y (wideband) and Q (narrow-band) color axes. I once was able to interview Dalton Prichard, the Guru of color receiver design at RCA Laboratories in Princeton. Dalton recalled that there was some patent dispute associated with the continued use of "I,Q" color demodulation, and that "one resistor was saved" in the matrix section of the 21CT55.

To support the additional power needs to drive the larger tube, the Vertical and Horizontal sections were "beefed up". A 6BL7 was used for vertical output and a more hefty 6CB5 was used for Horizontal Output. Three 3A2 tubes were used: one for focus rectification and two for High-voltage doubler rectification. A 6BK4 regulated the 25,000 volt second anode. As a convergence amplified used in the CT-100 was not needed, the CTC2B chassis had 36 tubes, the same as the CT-100. A small convergence chassis (CTC3) was mounted inside the right side of the cabinet. Removing the wood top of the set gave access to twelve convergence adjustments on the CTC3. (photos of the set interior and the chasses will be in the book). The set consumed 525 watts.

The set retailed for $895. It was rumored that RCA lost money on every CT-100 sold. If so, they lost even more money on the complex 21CT55.

The 21CT55 photo is from its original service manual. Don Kent did the PhotoShop colorization of this image.

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Copyright 1999, Ed Reitan .


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