Transform a Black and White TV Into Color Using Revamped Tech From the '50s

Before 4K flatscreen TVs were even a futuristic thought, people in the '50s watched TV on a 10" to 12" black and white monochrome CRT. Color TV did exist at that time, but it was costly, and not many of the six million people who had TV could afford the luxury. Color Converter Incorporated decided to cash in on the wonders of color TV by offering a device, known as Col-R-Tel, that could transform any B&W program into a full-color display by placing an RGB filter wheel onto the front of the TV.

The idea was that the wheel would spin at the same frame rates as the images on display, with all RGB stitching being done in viewers' heads, like an optical illusion. As you might imagine, the Col-R-Tel was bulky, could only fit TVs with 10" to 12" screens, and was powered by a series of tubes. It also had an MSRP of $150, which is about $1,457 today, meaning the price tag was not within reach of everyone. Electronics enthusiast MrSlehofer took interest in the Col-R-Telt and decided to replicate the device and pair it with a monochrome CRT in the name of science and see how well it could transform B&W video.

Instead of using a series of vacuum tubes like the original to drive the device, MrSlehofer designed his unit with only transistors and no ICs. The principle behind his module lies in demodulating only one color signal at a time, based on the filter color in front of the CRT, a process easier said than done.

"This is done through switching different carrier (color burst) phase offsets corresponding to R-Y (90°), B-Y(0°) and G-Y(236°)," MrSlehofer explains in his project blog. "The selected carrier phase is summed with the chroma contained in the NTSC video signal resulting in an AM signal amplitude of which is corresponding to the demodulated color difference signal level. This AM signal is then simply detected by a synchronous detector, combined with the luminance in the video signal and sent to the CRT."

MrSlehofer has uploaded a detailed schematic, along with a BOM and other documentation on his project page, for those interested in recreating his build.