Phonovision not digital?

[Viewmaster]

I am not up on inter channel breakthro' figures on discs, and how many db's down one channel is on the other, but with audio only recordings this is not troublesome.
But for NBTV with audio on one channel and vision on the other would this not be a very great problem on a stereo cut disc/cylinder?..........

........The slightest breakthro' would lead to the NBTV whining sound being heard and the sound would also modulate the picture.
I remember what sound breakthrough looked like on the 405 line TV...not a pretty sight.

Good point, Albert. I checked the specifications on some of the Ortofon pickups and mid-range separation is on the order of 25 db-not so good.

Now this channel separation is with the channels normally phased for the 45/45 system. With one of the channels wired out-of-phase for the "Baird" hill-and-dale video/side-to-side audio channel system, this might change. I need to think that over.

Before you do, check out the prices of stereo disc cutters. WOW!

Now I might consider going backwards in time to the guts of an old moving iron loudspeaker.
Horse shoe magnet/coil/armature with a cutter stuck on the end!

It would certainly look the part on a NBTV/phonocylinder machine.

Mono and cheap. Simple and probably no good!

I have bought a blank wax cylinder now (fools rush in!) and when I have
the time(!) will get an old moving iron LS and set about putting a stylus on it...then mount it on my model engineers lathe with the cylinder revolving in the lathe chuck. etc etc. Just to see what it can do with a range of various audio freq. inputs.
Albert.

[Stephen]

Before you do, check out the prices of stereo disc cutters. WOW!

Somehow I was hoping that there was going to be a glut of old stereo disc cutters on the market with the shift to digital media.

Now I might consider going backwards in time to the guts of an old moving iron loudspeaker.
Horse shoe magnet/coil/armature with a cutter stuck on the end!

It would certainly look the part on a NBTV/phonocylinder machine.

Mono and cheap. Simple and probably no good!

I have bought a blank wax cylinder now (fools rush in!) and when I have
the time(!) will get an old moving iron LS and set about putting a stylus on it...then mount it on my model engineers lathe with the cylinder revolving in the lathe chuck. etc etc. Just to see what it can do with a range of various audio freq. inputs.

What you might do is look for an old 1940s home-type disc cutter. They typically were radio/gramophone/cutter combos. You could either restore such a unit or use it for parts. Alternatively, you might find a cutter head for such machines. There were two common types, the piezoelectric and the magnetic. The piezoelectric types are often duds because the ravages of heat and humidity have destroyed the crystal element over time. The magnetic types should still work fine and you can drive them with an ordinary audio amplifier.

[Stephen]

With a casual search on the web, I found an American company that repairs old cutter heads for US$50. Of the brands that this company shows on their web page, probably the best one is the Presto, but that is probably the most difficult to come by. The Astatic types were very common.

See http://www.west-techservices.com/p2.htm for details.

[Viewmaster]

What you might do is look for an old 1940s home-type disc cutter. They typically were radio/gramophone/cutter combos. You could either restore such a unit or use it for parts. Alternatively, you might find a cutter head for such machines. There were two common types, the piezoelectric and the magnetic. The piezoelectric types are often duds because the ravages of heat and humidity have destroyed the crystal element over time. The magnetic types should still work fine and you can drive them with an ordinary audio amplifier.

Have revised my posting....Old cutters OK for mono but not for NBTV cylinder stereo, unless one could (I couldn't!) design circuits to completely balance out all the picture noise on audio chan and all the sound on the picture channel. As you said even a modern Ortofon pick up has only 25db chan seperation, so old stereo cutters would probably be worse, even if one could find a servicable one.
Albert.

[M3DVQ]

why use stereo? as it seems this causes all sorts of problems. if you have a seperate cutter/pickup for audio and video, 180º out of phase around the cylinder then you don't have any crosstalk etc to compensate for.
Obviously you only get half as much video on each cylinder, but it would seem much simpler

[Viewmaster]

why use stereo? as it seems this causes all sorts of problems. if you have a seperate cutter/pickup for audio and video, 180º out of phase around the cylinder then you don't have any crosstalk etc to compensate for.
Obviously you only get half as much video on each cylinder, but it would seem much simpler

Yes, halving the recording time on a wax cylinder is not a very attractive path to go down, with more mechanics of the two recording/playback heads mounting thrown in too.
One could make a longer cylinder of course, but I would prefer to keep to standard cylinders (and their speeds) which can be bought as blanks straight off the shelf for £7. More than the cost of a CD but also more exciting!
Albert.

[ac7zl]

Your comment evoked a memory:

When I was a child, a friend of mine had a talking GI-JOE army doll. When you pulled the string, it commented on some aspect of its adventurous life.

Even back then, I had the reputation of being something of a tinkerer, so I always ended up with "gifts" of broken things to take apart. When the doll quit talking, the afore mentioned friend gave me the torso to dismantle.

Inside were two small drums, one of them spring loaded (like a measuring tape). The other held the wound-up pull-string. A long strip of thick, black, plastic tape was wound and stored upon the spring-loaded drum, its free end anchored to the drum with the pull-string. When you pulled the string, the tape was transfered from one drum to the other, and the spring was placed under tension. When you released the string. The spring flexed, the tape was transferred back to the first drum, and the string was wound back up. I can't recall how the speed was governed, there was some mechanism to address that.

The tape was embossed with 6 or 8 grooves or tracks that contained the audio information. A reproducer mechanism, composed of nothing more than a plastic cone with a steel needle, was attached to the end of a short, pivoted arm. The arm swung freely and was allowed to fall randomly into one of the grooves at the start of the tape. This was a long time ago and my memory is vague, but I think the tape was somewhere between 3/8 and 1/2-inch wide.

It was really a nifty mechanism from a pre-digital electronics age.

Pete
AC7ZL

That gives me the idea of a third way of mechanical recording: Grooves on tape! There was the german system "Tefifon" which had some success in the fifties. It is using an endless tape with grooves. The advantage to a record was the very much longer playing time, which makes it ideal for video. And on a 1/4 inch tape you can put many grooves, which makes a fast switching between different grooves possible and you could use two grooves for separate sound and vision, or even a third groove for synch-impulses. A palyer for that system would be rel. easy and cheap to make, but I have no idea how they did the recordings.

[Stephen]

With all the complications of cylinder/disc cutters, I wonder if it would be worth considering a version of Fernseh's intermediate film system. One could use 16mm film running at constant speed behind a scanning disc for recording. Assuming that the film spooled laterally from left to right instead of vertically, the film itself could provide the displacement for each line from right to left so that the scanning disc would comprise a series of 30 or 32 apertures at a constant radius from the disc centre. After developing the film, the 16 mm film would then run at constant speed with the special scanning disc in front of it and a light source behind it to reproduce the recorded programme. In other words, for both recording and reproducing, the film would run laterally at a rate of 375 lines per second for the 30 line system or 400 lines per second for the 32 line system.

Of course, there would be no need for the on-the-fly developing system used with the Fernseh process. The film developing could be done in a conventional manner like any standard motion picture film.

[Viewmaster]

With all the complications of cylinder/disc cutters, I wonder if it would be worth considering a version of Fernseh's intermediate film system. One could use 16mm film running at constant speed behind a scanning disc for recording. .

Well, Stephen, I daresay that there are many ways to skin this particular cat, with steel tape/wire and your film idea too...even using CDs !

But as I said previously, for me, the bringing together of the first way that sound was recorded onto a cylinder and the first way that television was achieved with a Nipkow disc is an interesting historic project, so I shall soldier on with my cylinder design.

Also 16mm film is getting difficult to find and process and will be even more expensive than a wax cylinder blank, minute for minute probably.

One thing is for sure...any thought of using a stereo disc cutter is out because of the channel breakthrough we spoke of.
These cutters/pick ups are very acceptable for left/right channel sound only but will be no good at all for combined sound/NBTV picture channels.
Albert.

[Klaas Robers]

Indeed the bad channel separation might be a problem, as well for sound to video, seeing the audio through the picture, as for video to sound, hearing the video buzz in the sound.

That was the reason that I was so happy with the 100 dB channel separation of CD, which wasn't needed at all for sound, who cares about some channel crosstalk in stereo, where both channels belong to the same sound impression, but was very usefull for NBTV with sound.

[Stephen]

I did a few calculations for cylinder and disc frequency response that might help direct the best approach. The minimum wavelength that a stylus can reproduce is twice the length of the minimum transverse dimension of the stylus.

In the case of the standard 2.1875 inch diameter cylinder rotating at 160 rpm (2.66667 rev/sec), the surface speed is 2.1875×pi×2.66667 = 18.33 inches per second (ips). With a standard 2.7 mil (.0027 inch) conical stylus, the minimum reproduceable wavelength would be .0054 inch. Therefore, the maximum reproduceable frequency would be 18.33/.0054 = 3394 Hz. With a special elliptical stylus that would have a minimum dimension of 1.2 mil, the maximum reproduceable frequency would be 18.33/.0024 = 7638 Hz.

In the case of a 12 inch diameter 78 rpm (1.3 rev/sec) disc, the outer diameter surface speed would be 12×pi×1.3 = 49 ips. The maximum reproduceable frequency with a 2.7 mil conical stylus would be 49/.0054 = 9074 Hz. With the elliptical stylus it would be 49/.0024 = 20416 Hz. Assuming a minimum diameter of 6 inches, the inner diameter surface speed would be 6×pi×1.3 = 24.5 ips. The maximum reproduceable frequency response with the conical stylus would be 24.5/.0054 = Hz. With the elliptical stylus the maximum reproduceable frequency would be 24.5/.0024 = 10208 Hz.

This indicates that even with a special elliptical stylus, the standard cylinder rotating at 160 rpm could not adequately reproduce our standard NBTV signals. We would need to use the larger "Concert" cylinders or a higher cylinder speed. The 78 rpm disc would work fine with a reproducer that has a 2.7 by 1.2 mil elliptical stylus. Assuming a pitch of 120 grooves per inch, the 12 inch diameter disc recorded to an inner diameter of 6 inches would provide a playing time of 120×3/78 = 4.6 minutes. Using available 14 inch recording discs would provide a playing time of 120×4/78 = 6.2 minutes.

[Stephen]

Let us suppose that we were to use the 1885 Bell-Tainter constant groove speed disc system, wherein the cutter/reproducer and the planetary drive wheel remains stationary and the disc platter moves instead to provide constant groove speed. Let us select a surface speed of 24 ips that provides a maximum reproduceable frequency of 24/.0024 = 10 kHz with a 2.7 by 1.2 mil elliptical stylus. At an innermost diameter of 6 inches, the groove would have a circumference of about 19 inches. At an outermost diameter of 14 inches, the groove would have a circumference of about 44 inches. That would be an average circumference of about 32 inches. Therefore, the total approximate length of the groove recording from an inner diameter of 6 inches to an outer diameter of 14 inches at a pitch of 120 grooves per inch would be 120×4×32 = 15360 inches. At a recording/reproducing groove speed of 24 ips, that would work out to a playing time of 10.67 minutes.

[M3DVQ]

maybe there's a reason that this is the first idea you've come up with that Baird didn't already patent and develop...

[Steve Anderson]

I'm not sure if this is feasable, but if one used a Nipkow disc as the actual recording medium? That is you have something like a conventional LP record, just with holes in it at the appropriate places. The spiral groove would have to 'dodge' the holes, but you have absolute synchronisation!

Of course there is also the large area inside the drilled holes that could be used in the same way with no 'dodging' of the holes required.

All you do is change the Nipkow disc for a different recording.

Now who's going to have a go at a jukebox? (Please, no coin-slot).

Steve A.

[DrZarkov]

Thank you Stephen for your calculations. It clarifies a lot to me. So before we start on bulky concert cylinders or our own "norm" of cylinders it would be easier to work with discs, like Baird did before. I liked the idea of a Phonograph system and I still do. But does it make any sence if we don't want to use a 320 rpm system with half a minute recordings?