Vintage Monoscope Tubes Generate Classic TV Test Patterns Once Again

Night creatures and insomniacs of a bygone era may fondly recall a TV test pattern appearing once [Jack Parr] or [Steve Allen] had had their say and the local TV station’s regular broadcast day had concluded. It was affectionately known as the Indian Head test pattern, for the stylized Native American, resplendent in a feathered headdress, that featured prominently in the graphic.

Unknown to most viewers was exactly how that test pattern and others like it were generated. But thanks to [Rich “The Lab Guy” Diehl] and his monoscope restoration project, we can all share in the retro details. It turns out that while some test patterns were merely a studio camera trained on a printed card, most were generated by a special tube called a monoscope. It functioned in basically the same manner as a studio camera, but rather than scanning the incident light of a scene with an electron beam, the image was permanently etched into a thin aluminum plate. [Rich] laid hands on two vintage monoscope tubes, one containing the Indian Head test pattern, and set about building a device to use them. “The Chief” can hold either tube in a Faraday cage of thin, flexible PCB material and 3D-printed parts, with supporting electronics like the power supply and video amplifiers in an aluminum chassis below.

It’s a nice piece of work and a great lesson in how it used to be done, and the lithophane of the Indian head is a nice touch. Hats off to [The Lab Guy] for build quality and great documentation, including a detailed video series that starts with the video below. If you need a little more background on how video came to be, [Philo Farnsworth]’s story is a good place to start.

[via @TubeTimeUS]

15 thoughts on “Vintage Monoscope Tubes Generate Classic TV Test Patterns Once Again

  1. Simply referred to as the “test pattern” in the television program guide printed in U.S. newspapers during the mid-1940’s, this comprised a large chunk of the broadcast day, and was the only thing that could be seen on any channel (there were only one to three channels in most cities) until the actual start of programming. Typical start would be sometime between 10 a.m. and 3 p.m. Up until then, there was nothing to be seen but “snow”, the moving pattern of dots that resulted when there was no signal. Then, at startup there was a “beep” in the audio, and the test pattern appeared, usually the “Indian Head” with the call letters of the station. Depending on the station, the audio was either silent, or had instrumental music with the pattern. On the hour an announcer would say “This is (call letters) broadcasting from (name of city)”. This sequence would continue until the actual start of the “real” television day, usually no earlier than 6 p.m. The first program was most often the news, which was a talking head reading a teletype printout the same as on radio (no other pictures or videos). How exciting. After the last program ended (usually 10 or 11 p.m.), some stations just “signed off” with the call letters briefly flashed on the screen. Others followed that with the Indian Head pattern again for about five to fifteen minutes, after which the image would revert to no-signal snow until the next day’s startup beep.

    1. Thanks for the trip down memory lane. The stations I watched when I was growing up would do almost exactly this, at least until cable TV became a thing in our area. It seems that cable companies didn’t like dead air, judging by my memories from that time. I seem to remember that cable channels were almost all 24 hour channels, and I suspect that the cable companies actually added their own programming in as fillers during the hours that the local channels were off-air.

      1. My favorite memory of ending the broadcast day was “High Flight”, followed by Massenet’s “Meditation” with crashing ocean waves. The peace of mind was then shattered with the National Anthem instrumental, and punctuated with all night color bars accompanied by an annoying audio tone.
        Great. Lull me into peaceful sleep, then jolt me awake and annoy me “til I get up, walk over and twist the knob to the off position.

        1. Ah, yes, “High Flight” by RCAF Pilot Officer John Gillespie Magee, Jr. According to the legend, he penned it on the back of a letter to his parents, and mailed it, shortly before he was killed in a mid-air collision during a training flight in the early years of World War 2.

  2. In Dallas, in the late 50s, early 60s, the TV stations would sign off by playing the Star Spangled Banner. Some of the stations showed the FBIs 10 most wanted list first. Then, sometimes test pattern for a while, sometimes not – I assumed the test pattern was displayed when they were tweaking the transmitter.

  3. no we have 100’s of stations playing program material 24hours a day and still there is no more worth watching than in th days when the one or two stations would only broadcast for half a day…

    1. Yep. There is probably less to watch today on TV than back when there were only a handful of stations.

      Even the 24 hour news stations are just as bad. They only have about 6 hours or so of programing so they put in on a loop.

      IMO TV today is total pap. It reminds me of that old ABC series called MaxHeadRoom which essentially parodied modern television of the future that was filled with mindless reality and game shows – just like we see today.

    2. Bruce Springsteen wrote a song about that a quarter century ago. Since then print media has died, timeshifting has become unnecessary, and streaming is on the verge of replacing prime time as the venue for high budget programming. Those 100 channels will disappear before they improve.

  4. I have no clue what crapshoot of “Chinese” printer he bought, but I recently purchased the Ender 3 for around $180 and it works like a charm from day one (and it looks by far sturdier than his plastic shoebox).
    Just saying…

    1. My printer is the Robox CEL and was made in England. It’s built like a tank. It worked first time and every time. I had no interest in being a 3D printing guru. Just getting the job done. The first printer I bought was $180. It NEVER worked.

  5. This guy picked up/preserved another Monoscope tube from CBS Hollywood and sent it to the Early Television Foundation (who then documented the image it contains)
    https://www.youtube.com/watch?v=8yb_aPM7Qyk

    Here in Australia the networks used the Philips PM5544 test pattern. Still have memories of being up early in the morning (mid 80s through early-mid 90s) and you would get color bars (not sure if SMPTE or otherwise) then the PM5544 (with the station name on it somewhere) and some music.

  6. Monoscope tubes are interesting, but I sort of liked the “flying spot scanner” used in things like the B&K “TV Analyst” piece of test equipment. It’s been close to 50 years since I’ve seen one, but, as best as I remember, they used a small CRT, with an ultra-fast phosphor, along with a photomultipler tube (Was it a 941?), to scan something like a 35mm slide. They’d scan the electron beam across the face of the CRT, which had the slide mounted right in front of it. The PMT was on the other side, and the light was collected via a lens, so that it focused on the PMT cathode (Or, something like that; Hey, it has been almost 50 years since I’ve seen/used one.). Thus, you could change the image being sent, by simply inserting a different slide.

    However, as far as beautiful tubes, the RCA 5820 Image Orthicon tube has to be one of the most beautiful ones. And, the fact that those things can be made to work at all is nothing short of amazing. I think I still have one stashed away somewhere. Maybe.

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