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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 9th Mar 2019, 12:50 pm   #1
Ian - G4JQT
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Default Build a TV?

If anyone was going to build a 405-line TV (single channel?) which design would you follow from all the published DIY TVs from the 1950s out there?

Most important item would be availability of a tube, and availability of replacements - just in case. Other things to bear in mind would be RF and IF coils - either widely available from junked stets, or rewindable.

I see some of the scan coils have designs to make on a home-made jig. Wonder how good those would be? Or maybe electrostatic deflection would be the way to go in a home-brew TV. But the electrostatic tubes...?

Ian
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Old 9th Mar 2019, 2:04 pm   #2
Argus25
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Default Re: Build a TV?

There are plenty of scope tubes out there to make an electrostatic deflection 405 line TV.

There are numerous articles on how to do it. The one UK TV experimenters were keen on was the Argus, that used the VCR97 CRT, these are still available from time to time.

However many American 5" scope tubes with P1 (green phosphors, like the VCR97) can be substituted to make an Argus.

The only problem with P1 phosphor is that it makes everyone look like the incredible Hulk. (Aka Dr. David Bruce Banner who was accidentally overdosed with Gamma radiation and whenever he is angry or outraged transforms into the Hulk. For example, changing his car tire he gashed his hands on the pavement, got angry and tossed his car over an embankment...grrrrr). Pretty cool really, and Marvel are making a big comeback.

Here is an Argus TV I made:

http://worldphaco.com/uploads/ARGUS.pdf

The problem with electrostatic deflection, is that most CRT's suited to it, run from relatively low EHT voltages, 3kV or less for small'ish CRT's. Large electrostatic CRT's become impractical due to the high deflection voltage requirements, though PDA CRT's help a little to ameliorate this problem.

The advantage of magnetic deflection is you can run higher EHT voltages, have higher "screen energy" (contrast and brightness) and generally better results. (the electron energy, or electron.volts are higher)

So I would recommend, if you are building a vintage set "replica" to use magnetic deflection with an aluminized CRT, and an EHT of at least in excess of 7kV if you want a good bright high contrast image.

Most (but not all) modern P4 phosphor CRT's have an aluminized screen, so they need over 5kV to penetrate the aluminium layer to get any reasonable light output from the phosphor. Non aluminized screens can work well down to 2kV EHT.
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Old 9th Mar 2019, 3:41 pm   #3
Radio Wrangler
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Default Re: Build a TV?

Most scopes without PDAs and without aluminised screens ran at about 1.5 - 2.5kV cathode to screen. With that amount of acceleration and the current their cathodes could run, you got a reasonably bright scope trace.

But remember that a scope trace is only a 1-line picture.

Share that spot power over the whole screen area and the picture you get is very dim. Much higher total acceleration voltage is needed. Having the electrons going faster through the deflection area makes for very insensitive deflection electrostatic plate voltage swings would be problematical.

So go for a tube with 7-14kV on the final anode and magnetic deflection.

David
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Old 9th Mar 2019, 8:18 pm   #4
kellys_eye
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Default Re: Build a TV?

I have the original issues of Practical Television that covers the construction of a set from 'ground up' (625-line though). Could forward a scan of the articles if enough interest?
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Old 9th Mar 2019, 10:36 pm   #5
Philips210
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Default Re: Build a TV?

Hi.

There was the "Olympic II" transistorised 405 line receiver. Details can be found in this book at the internet archive.org https://archive.org/details/PracticalTelevisionCircuits It looks a great project to build but I think a number of wound components will be very difficult to obtain.

Regards,
Symon
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Old 9th Mar 2019, 11:18 pm   #6
Argus25
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Default Re: Build a TV?

Since there are a lot of aspects to a TV design, from scratch, there is a method that will get you half way there, the other half is still a challenge if you want home made.

If you get a cheap monochrome video monitor (even a 625 line type) and you can modify it to 405 lines later if you want, then you could set yourself the task of building the RF and IF sections. You will have to decide if you want to go for a superhet and or a tuner box on the front end, or a TRF type typical of early 405 line sets. Once you have perfected the build you would then learn about how to sweep the IF (Or TRF stages) to check the video bandpass response and the correct audio channel response.

This is how I started to build TV's, with the radio frequency stages and challenges first. After that I went on to building video monitors from scratch and then combining everything, with the audio amplifier etc to make a complete working TV. On the video monitor side of things there are the line & frame scan circuits, sync separatror, EHT and CRT support circuitry such as the video output amplifier, all which has to be working well to get a good picture. This is why starting with a good monitor is a big help for an initial attempt.

Hers is a video monitor that I modified to run on 625/525 or 405 lines and there are clues in the article on how to modify the scanning & deflection circuits to make that happen:

http://worldphaco.com/uploads/Autode...e_monitor..pdf

Another trick to get you there more quickly, especially for a valve set, is to find a scrap TV chassis that has a separate IF strip. If you get that and the tuner box and start with a power supply on a new chassis, you can learn how to align it properly, and test the final result with a scopr & video monitor, being aware that they have a low input impedance so you would need a buffer stage or at a minimum un-terminate the video input or they will load down the video detector and you have to ensure the video feed to the monitor is correct (neg going sync). After that, you can then add your own CRT/scan coils and stages to the chassis.
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Old 9th Mar 2019, 11:54 pm   #7
Radio Wrangler
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Default Re: Build a TV?

Nowadays, though, you'd have to rationalise the oddness of building a tuner and demodulator for signals which are no longer available off-air and for which you'd have to build a signal source of some kind.

David
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Old 9th Mar 2019, 11:55 pm   #8
natlock
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Default Re: Build a TV?

An interesting twist might be to try and design the most modern single channel system A possible today. A greyscale LCD and digital signal processing ?
Just a thought..
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Old 10th Mar 2019, 12:29 am   #9
Argus25
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Default Re: Build a TV?

Yes all the anaolg TV RF signals now have to come from a box (like an Aurora). So logically using just the video signals and audio, all that is required is the video monitor, audio stage & speaker. However, a lot of the fun is to make the radio frequency stages as they would have been in a vintage TV, or what has been made is only 1/2 a "TV".
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Old 10th Mar 2019, 6:36 am   #10
Ed_Dinning
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Default Re: Build a TV?

Hi Ian, freeview box that gives out baseband video and audio would be an easy way to get over the RF design side of things.
An ES tube would be ideal from the point of view of 405/625 operation, but I have made scan coils for EM tubes to a design in WW from the 50's.
I believe there were also scan coil winding details in Electronic Engineering and PTV.
I may have some PDA tubes if you are interested, PM me in a couple of weeks when I will have access to them and various vintage TV components.

Ed
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Old 10th Mar 2019, 8:13 am   #11
Argus25
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Default Re: Build a TV?

If you want to go down the road of a classic Pre-war style electrostatic deflected CRT (using a 5 inch tube, 5BP1 or 5BP4 or any similar scope tube) you could model the set on the Meissner Kit or the Andrea KTE-5, both kits that came out in 1939.

They are very easily adjusted to other scan frequencies and the RF frequencies altered, they can be made to display 405 line video too, with small alterations to the scan circuits and video detector.

The Meissner circuit/assembly manual is here (I found the manual on the net), all common garden valves:

http://www.myvintagetv.com/Apple%20P...s/Meissner.pdf

I have restored examples of both of these electrostatic TV sets, the Tech is virtually identical. Here is an article on both:

http://worldphaco.com/uploads/THE_ME...DREA_KTE-5.pdf
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