30 line Televisor project.

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30 line Televisor project.

Postby cool386 » Tue Mar 08, 2022 1:59 pm

As my first post, I should introduce myself as a vintage technology enthusiast (particularly TV) from way back. Being in Australia, the oldest commercially made sets date from 1956, though I have imported a couple of earlier sets from the U.S.; a mirror in the lid 10" set and a 7" cheapie, which can be seen on my website https://www.cool386.com
It's been a long time in the making, but I've finally finished my 'sort of a clone' of a Baird Televisor. I've had a fascination with mechanical TV since my school days, but it's only as time went on and I had access to a well equipped workshop, that I could make a proper go of it. I've been through the cardboard/plywood/gramophone record scanning disc experiments, but not with any success in my younger years. To cut a long story short, I later built up a Televisor for the Baird format, using the measurements from "Television for the amateur constructor". I believe the baseboard and disc dimensions are identical to the Plessey Televisor marketed by Baird. I took pics of my creation, as it was a few years back, which can be seen here https://www.flickr.com/photos/13469158@ ... 8070450870

rsz_dsc08024.jpg
televisor


I've got a proper sync circuit using the 375Hz line pulses. Although my transmitter (yet to be completed) will provide blacker than black sync pulses, my receiver would no doubt work on Baird's black level 'sync' pulses. The design is loosely based on that used for the CBS colour wheel receivers, using a 12AU7 phase detector to compare the sync pulses with pulses coming from a separate set of holes in the disc.

rsz_dsc07994.jpg
sync lamp


The error voltage controls the motor using a 6J6 cathode follower to drive a 2N3055 in series with the motor. Light source was originally a 4W fluorescent tube which gave the right colour and had good brightness, but at the time I didn't take into account the phosphor persistance. Having now switched a 44 LED array, the difference is like between night and day. And the LED's are easy to modulate with the existing 6EM5 output stage.
Circuit of the whole thing uses 6 valves and 4 transistors. I'm more than happy to go into further detail about the design if there's any interest.

Anyway, since I've not completed the transmitter, the question arises of what video signal to feed it. All I have are 375Hz sync pulses, which of course just gives a black bar and blank raster, and some old 32 line files I downloaded from somewhere (possibly even here?). Problem is they only run for 5 seconds, and the 32 line signal is of course not properly compatible (the sync works great though!). To view the 32 line video on a 30 line disc requires the disc to be run at 13.33fps instead of 12.5fps in order to get the correct line rate 400Hz, but of course the result is a slowly rolling picture from right to left, since the frame rate is now too fast.
As you can see, my hole marking out wasn't as accurate as I'd like - such is the use of hand tools - but as I bolted both transmitter and receiver discs together when I drilled them, I'm hoping the errors will cancel out once I have my own signal.

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nbtv
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https://youtu.be/TL5le6Sujkg

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girl
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https://youtu.be/IhmrreLmxlY

So, my question is - where can I get a 30 line signal? I might come across as an eccentric nutcase, but I genuinely want to watch real TV on this set - sit down for a 2hr James Bond movie, etc. (All of my TV viewing is actually on vintage sets, though of the electronic kind). Some years ago there was a standards converter that would produce every kind of vintage video format - including Baird's. Is this still available or has something taken its place? While vintage TV and electronics is second nature to me, anything microprocessor is not - and because of the vastly different formats I can't see any other practical way to do the conversion. I presume one would have to store the horizontal scanned 625 line pic (or ignore interlace and treat it as 312.5 lines) and then read it out as a 30 line vertical scanned signal with the edges cut off.
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Re: 30 line Televisor project.

Postby Harry Dalek » Tue Mar 08, 2022 8:10 pm

Nice job looks very well made a keeper for sure .
As far as a video signal thats easy just look in software on this site FreeNBTV does any line frame rate up to 240 lines you want but of cause you really have to drop the frame rate for the higher line rate to fit in your pc sound cards bandwidth other wise all washed out ..but yes Garys video2NBTV will do standard vintage line frame rate and your Baird standard video want.
scan down the page
https://www.taswegian.com/NBTV/forum/vi ... =41&t=2745
Welcome to the forum nice to have another Aussie on some come some go ; ) do review past posts theres a lot of good information on the forum and if you like vintage television information 20s 30s and a bit on later dates Bairds grandson is a member and the great Chris Long
https://www.facebook.com/groups/1705083 ... &ref=notif
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: 30 line Televisor project.

Postby Klaas Robers » Wed Mar 09, 2022 12:34 am

The NBTVA club, see at NBTV.org, has still the NBTV-compact discs. Disc 1 has NBTV only in the 32-line standard, but discs 2 and 3 have program in 32 lines as well as in 30 lines. Each disc will give you about half an hour of uninterrupted NBTV video (on the left channel) with accompanying sound (on the right channel). So, if you have a CD-player you can enjoy your Nipkow disc monitor.

The 30 line video contains blacker that black line pulses, but no frame pulse. This was more optimal for the vintage Baird televisors that are still existing in the UK. You can obtain the CDs from the clubshop, now done by Chris Lewis.

Good Luck!
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Re: 30 line Televisor project.

Postby cool386 » Wed Mar 09, 2022 6:59 pm

Many thanks for the software links. Coincindentally, I also joined the fb group a few days ago. I also have a video from about 30 years ago that features some of Chris Long's work.
The software converter is just what I needed. It works well in 32 bit Windows 7, although it can only be shut down via the task manager, which in itself is not a problem.
A nice surprise is the input from the computer's internal camera. This takes care of the conversion from 625 lines, simply by placing the laptop in front of a 625 line TV. Conveniently, the Baird frame rate being an exact sub multiple of the 50 field rate means there's no beat pattern.

Such is the additiction of my new toy, I've wasted most of the day watching off air TV on 30 lines...

Some things I've observed: 1) If I'm to get entertainment quality off air pictures, I'll have to correct some of the hole positions from lines 23 to 29. That means the transmitter disc would also need the same correction. 2)I suspected I might need it, but a switch to remove the sync pulses during adjustment of the frame phasing.
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Re: 30 line Televisor project.

Postby Klaas Robers » Thu Mar 10, 2022 3:45 am

By the way.... The same NBTVA club shop has Nipkow discs in several materials and sizes. Ask Chris Lewis about. They are all 32 lines, for which there is more NBTV video on Compact Disc available, e.g the MUTR disc (see http://nbtv.org/MUTR-disc) down loadable from the website. And the NBTVA Nipkow discs are made with high precision.

You have already experienced that it is difficult to make a disc with quite some precision (it should be about 0.01 mm or better), which is almost undoable by hand. So these discs are computer drilled or punched. Although it is chalenging to think about making such a disc yourself. Our former member Dennis Asseman (Belgian) once punched such discs on a specially made rather large punching table. You may find pictures of him doing that.

The first experience is the best. When you see a picture coming from your own drilled or punched disc, how ragged they are. At least you SEE something. So it WORKS.

Succes!!!
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Re: 30 line Televisor project.

Postby cool386 » Thu Mar 10, 2022 11:16 am

Klaas Robers wrote:You have already experienced that it is difficult to make a disc with quite some precision

So true! I can certainly see this now with a real video signal. Since this forum doesn't allow me to post in real time, my comments on this yesterday have not yet appeared. Back in 1993 when I had the discs cut out (by water jet), all I had was a steel rule and protractor to mark out the holes. I used a 1mm drill bit in a press, with both discs bolted together - the idea being that any errors would cancel out.
No doubt, the home made discs in the 1930's gave a picture quality similar to what I have at present.
I had heard of the 32 line system, from a video by Chris Long, but as I was reproducing the Baird standard, and 12 degree holes are easier to mark out than at 11.25 degrees, the obvious choice was to stick with 30 lines.
I noticed the NBTVA manufactured discs as I was looking through some posts here, which could be of interest, especially if they're 20" as per the Baird specification. Since I'm interested in off air TV viewing and making my own material, the number of lines is not important. My ultimate goal of course is to obtain a Plessey Televisor, but that's another story.
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Re: 30 line Televisor project.

Postby Lowtone » Fri Mar 11, 2022 3:23 am

r a d i o P T T v i s i o n
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Re: 30 line Televisor project.

Postby Klaas Robers » Fri Mar 11, 2022 4:35 am

cool386 wrote:I had heard of the 32 line system, from a video by Chris Long, but as I was reproducing the Baird standard, and 12 degree holes are easier to mark out than at 11.25 degrees, the obvious choice was to stick with 30 lines.

That looks easier, but better than using the degrees, is to divide the 360 degrees circle.
Divide by two, four, eight, sixteen, thirty two......

Do this on a large board by large compasses or other means. Remember your lessons in mathematics. Dividing an angle by two is easy and can be done with rather high precision. This is not possible with 30 lines, because dividing an angle by 3 and/or by 5 is an unprecise operation. That is the reason that about 50 years ago Doug Pitt, the founder of the English club, went for 32 lines.
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Re: 30 line Televisor project.

Postby cool386 » Fri Mar 11, 2022 12:11 pm

Klaas Robers wrote: That is the reason that about 50 years ago Doug Pitt, the founder of the English club, went for 32 lines.

Very interesting. Until now, I had assumed the choice of 32 lines was to do with electronic displays; being suited to digital dividers counting down from the line frequency to create a frame sync pulse. But now that I see the 32 line waveform does contain a 12.5Hz frame pulse, it kills off that theory.
Since it is getting onto 28 years ago that I marked out my discs, I can't remember exactly how I referenced the protractor, but I suspect I simply referenced it to line 1, and then turned it around when 180 degrees was reached. From my early metal work days, I knew not to just add 12 degrees to each line as I marked them out, since there would be a very bad cumulative error by line 30.

Thanks Lowtone for the Aurora info; great to see it's still available. It's come a long way since I last looked. I don't see any reference to composite video output for mechanical sets however, but it seems to only provide separate sync and vision signals to drive the lamp and phonic wheel directly. Not a problem though, since combining them into a 1Vp-p composite signal is easy. The 405 line output is also an added incentive to investigate purchasing one.
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Re: 30 line Televisor project.

Postby Steve Anderson » Fri Mar 11, 2022 2:57 pm

Just a quick note...once your 5th posting is approved by Andrew, Dave or I, further messages will appear immediately. Instigating this quite some years ago has all but eliminated spammers and the like...

Steve A.

P.S. I admit I thought that 32-lines was derived due to/for electronic reasons too. I stand corrected!
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Re: 30 line Televisor project.

Postby cool386 » Sun Mar 13, 2022 12:09 am

The details of the Televisor are now on my website https://www.cool386.com/televisor/televisor.html
And the YT video https://youtu.be/LEeXEPF7vTc
I'm waiting on a reply re the Aurora standards converter for price and availability. Next part of this project will be to continue on with the transmitter, and to see if the disc errors cancel out.
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Re: 30 line Televisor project.

Postby Klaas Robers » Sun Mar 13, 2022 2:48 am

No Steve, the 32 lines was choosen because it is easier to construct angles of the positions of the holes in the Nipkow disc. In the same moment the aspect ratio of Bairds 3 : 7 was changed in 2 : 3, because the 3:7 gave a very narrow picture and 2 : 3 is a well known portrait format.

And also at almost the same moment the "missing" frame pulse came in. This was all about anno 1980.
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Re: 30 line Televisor project.

Postby Steve Anderson » Sun Mar 13, 2022 12:54 pm

Understood, it's a good thing I guess that 32 is a easy binary number and a simple geometric progression.

The 2:3 aspect ratio was also a good choice in my opinion though not historically correct, the 3:7 really is too narrow. I wonder why it was chosen? I guess some technical constraint at the time.

2:3 isn't that far removed from the "Golden Rectangle" of 1.618...the ratio has some artistic merit as well as geometric...

https://en.wikipedia.org/wiki/Golden_re ... 0as%20well.

Steve A.
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Re: 30 line Televisor project.

Postby cool386 » Sun Mar 13, 2022 5:57 pm

Re the choice of a 7:3 vertical scan, the following from "First Principles of Television", 1932, has this to say:

rsz_aspect.jpg
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Re: 30 line Televisor project.

Postby Harry Dalek » Sun Mar 13, 2022 6:27 pm

[quote="cool386"]Re the choice of a 7:3 vertical scan, the following from "First Principles of Television", 1932, has this to say:

Reading the papers from the time they gave this one 100khz bandwidth
Waterloo Evening Courier
Oct 26, 1929, Page 16
Waterloo, Iowa, US
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