Mechanical TV / Televisor designs ??

[lloydwells]

Ok so after years of having a bit of a thing for mechanical TV I finally bought one of those tiny educational kits and I'm kinda impressed by it BUT! I have a bad thing for going as vintage as possible so the want has arisen to actually build one. Now I'd quite like to build a replica of an actual production set of the period with no nasty modern bits what I need is some information on measurements of parts speed of motor for say a Baird televisor and some sort of guidance on what seems to be a very vaguely described Sync system can anyone enlighten me ?

[Tractionist]

I think Steve Ostler [on this site: AKA Panrock] has done a considerable amount of research and 'invention' in this field.

[19Seventy7]

I've been interested in mechanical TV for quite some time too, I've done some research on building one. I found that 750rpm seems to be the minimum you can go for a motor speed. IIRC the sync system was done by adjusting the speed of the motor with some form of pot/variable resistor? I could be wrong of course.

Will be following this thread with interest

Where did you get your kit from? I've been thinking of getting one for some time but have never actually seen any for sale

Cheers, and good luck
'77

[Cobaltblue]

Originally from here

https://mindsetsonline.co.uk/shop/televisor/

Bought mine many years ago.

You might find this article helpful as well

https://www.bvws.org.uk/publications...olume11number3

Cheers

Mike T

[lloydwells]

Had a bit of a look at that it's not particularly instructional for making anything other than a lamp.the Baird used what would essentially amount to a synchronous motor attached to the back of the disc motor which kept the disc motor in sync it's this that I really need a bit more detail on the rest of it with the exception of measurements is pretty easy. The problem with the televisor is nobody seems to have actually bothered drawing out the wiring or doing any half decent photos of the components of it. Ideally id like to be feeding it signals from a period radio as the bandwidth is low that shouldn't be difficult.

[TonyDuell]

I suspect that modern televisor kit is similar to the attached circuit diagram. There is a programmed PIC in it, but it's only used to generate the test card display, the actual sync/led driver sections are standard parts. IIRC there is a sync pulse for every line (corresponds to a notch in the disk going through a slotted optoswitch) with one missing for the frame sync.

As for the original Baird unit, alongside me is a book entitled 'Television for the Amateur Contructor' by H. J. Barton Chapple, dating from 1933. Most of the book is on the 'electronics' -- the (TRF) radio receiver, neon bulb driver, etc. But there are chapters on making a televisor essentally from the Baird kit (with the wiring diagrams, photos, layout, etc) and one on making rather more from scratch including punching the disk yourself, making the synchroniser, etc.

[Panrock]

Yes, building a mechanical televisor is great fun!

As for synchronisation, the early mechanical televisors simply passed the video signal through coils either side of a magnetised rotor... the so-called "phonic wheel". The 375 Hz periodicity of the varying video signal was enough to do the trick. I understand that rotating the position of the whole assembly could then take care of the frame phasing.

Things have advanced since the early days though... the standard is now 32-lines - not 30! And there are proper sync pulses. One is missing every frame, to serve as the frame sync.

You'll find joining the NBTVA (Narrow Band Television Association) useful. http://nbtv.org/ They can supply things like precision-cut Nipkow Discs, printed circuit boards such as for the sync separator, http://www.nbtv.wyenet.co.uk/cammonsync.htm and also audio CDs with pre-recorded NBTV signals on.

There's a specialist discussion board on NBTV at https://www.taswegian.com/NBTV/forum/

As regards the results, 30-line television inevitably has something of a 'peep show' quality to it. The pictures from most Nipkow Disc displays tend to be small, dim and flickery. With some effort though, it's possible to use mechanical television technology to achieve quite watchable results, even by today's standards. For example my 120-line, 25Hz frame rate, colour mirror-screw.

Anyway, welcome to the world of NBTV!

Steve

[lloydwells]

I'll find joining the NBTVA a pain in the ----- I've been trying to make contact with someone for about three days.

[Panrock]

Originally Posted by lloydwells

Now I'd quite like to build a replica of an actual production set of the period...

Colin Sanderson - Brigham on this forum - has built such a replica. Excellent it is too.

Here are two examples of my 120-line mirror screw system in action. The frame bars are camera artifacts. The nearest ancient equivalents to this were made by TeKaDe in Germany in the early 'thirties.

https://www.youtube.com/watch?v=ELk4DmqwNms
https://www.youtube.com/watch?v=Vf5Po5n1--k

More on mirror screws at https://www.earlytelevision.org/Yanc...history-1.html

Originally Posted by lloydwells

I'll find joining the NBTVA a pain in the ----- I've been trying to make contact with someone for about three days.

If you've tried the various methods at 'How to join the club' at www.nbtv.org without success, then PM me and I will give you the NBTVA Chairman's direct email address.

Steve

[peter_scott]

It's great pity that videos of the mirror screw have out of sync framing. I'm sure it is much more impressive when watching it live and free from black bars.

Peter

[Panrock]

Maybe, if you can visit here sometime Peter, armed with your inestimable know-how and a suitable camera, we can do better.

Steve

[peter_scott]

Sorry Steve, I didn't mean to criticise, only to suggest that the real thing is better than the video shows. I've similar problems with Baird 240 lines and don't have any camera that can capture it for YouTube.

Peter

[Panrock]

No umbrage taken at all; just a genuine invitation so I might benefit from your skills. Your capture of that Test Card on your pre-war HMV has set a standard of excellence.

But yes, filming a mirror screw in action is 'difficult'. The late Karen Orton had a go when she visited me, carrying a high-end portable video camera. She didn't succeed.

Steve