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45 line televisor

PostPosted: Wed Oct 31, 2018 3:54 am
by kd6cji
I've got a 45 line triple interlaced club disk and started the project past weekend. I decided to go with synchronous motor (1800 rpm @ 60Hz) and 2:1 timing belt reduction drive. As for the LED driver, the plan is to build a one tube driver using 117N7GT tube and 30 orange LEDS in series. I've seen the mentioning of tube driver here on the discussion board, but could not find any details. Did anyone built one? If so, can you share the design? Thanks!

Re: 45 line televisor

PostPosted: Wed Oct 31, 2018 5:50 pm
by Steve Anderson
A tube/valve (UK-speak) LED driver is on my long list of "Things To Do"...this may give me the impetus to do something about it...

Can I ask why you chose this particular tube? Perhaps you have a few already? There are others that are better suited to be honest.

These 117-volt tubes were introduced to eliminate the cost/size/weight of a power transformer - but that potentially (excuse the pun) is dangerous - even on the lower 117V supply compared to most other countries. The heaters in these tubes are very fragile due to the very thin heater wire required to get the correct resistance, power and temperature.

The only way to make this safe would be to use an isolation transformer (117V to 117V) and ground any exposed metalwork as well as the circuits. In which case you may as well get a conventional tube radio power transformer...

Steve A.

Re: 45 line televisor

PostPosted: Thu Nov 01, 2018 2:20 am
by kd6cji
Well, this is the reason to use it. No power transformer. I have a few of those valves in my junk box too. I am going to use polarized 3 prong power plug, so all metal parts will be grounded which sort of reduces a little risk of electrocution. Plate current and power should be enough to drive string of 30 LEDs. As I am using synchronous motor, there is no sync pulses and therefore no DC restoration, so a simple audio amplifier circuit should work. A year or so ago, I built a regenerative receiver with 117N7GT as audio amplifier and 12K7 as a detector tube, also I used this tube in a QRP 40m CW transmitter... and still alive ... :shock:

Re: 45 line televisor

PostPosted: Thu Nov 01, 2018 9:44 pm
by Andrew Davie
This project sounds dangerous and potentially lethal.
You may feel competent working with this, but I must think of others reading and perhaps following in your footsteps.
The formal policy of this forum is
a) don't do anything for which you do not have skills/training
b) anything you do decide to do is of course totally at your own risk
As to this project; please heed the advice and find a safer way.

Re: 45 line televisor

PostPosted: Fri Nov 02, 2018 12:10 am
by smeezekitty
I've seen quite a few 117V tubes with blown filaments. I don't see why you want to avoid a power transformer. A transformer to run 1-2 filamentous isn't all that big.

Re: 45 line televisor

PostPosted: Fri Nov 02, 2018 1:16 am
by kd6cji
The main danger of not using an isolation or power transformer is the possibility of the reverse connection to mains when neutral wire is feeding the plates and hot wire is on the chassis, then there is a potential to be shocked by touching the chassis. With the polarized plug the danger is minimized, furthermore I am going to put a neon indicator lamp between the neutral wire and ground, in case the wall power socket is wired incorrectly the lamp will light up as a warning. I used this technique before. As for power transformer it is not a filament transformer that is the problem, there are plenty 6V transformers available, but rather HV transformer. At the end I may forego the tube approach and go with transistors, but want to try tube first. Also, I am not advocating this approach and not encouraging anyone to try it.

Re: 45 line televisor

PostPosted: Fri Nov 02, 2018 7:43 pm
by Robonz
I love your project, and very keen to see you get this going. I used to pull apart my parents TV when I was 13 years old I did it when they were not home so I would not get in trouble. Sometimes it took me a long time to fiddle all the potentiometers back in place and I would get a little nervous. But it was fun to me. So long as you are aware of the dangers and are careful I am sure you will do well.

I really like that you have chosen to do a tube based driver rather than a silicon version. It will add a lot of authenticity to your project. I have a bunch of valves here but I am too lazy to use them. I enjoy the mechanical challenge myself.

I look forward to your next update.

Re: 45 line televisor

PostPosted: Fri Nov 02, 2018 9:53 pm
by Steve Anderson
I have decided to withdraw from this thread due to my safety concerns regarding other members/readers who may desire to follow this example.

To those I strongly suggest you DO NOT.

One day I may get around to doing a valve/tube-driven LED array for NBTV, but be certain it will include a transformer to remove the risks involved in direct non-isolated wall-socket power supplies.

The OP may still be alive, others may not be so lucky or experienced.

Steve A.

I'm sorry kd6cji but I cannot endorse this in any shape or form and distance myself from it entirely.

Re: 45 line televisor

PostPosted: Sat Nov 03, 2018 6:35 pm
by Harry Dalek
I would go with a transformer if any thing if it ends up in some ones hands in the future more than likely some one interested in tinkering with it and they are not careful its best you save their life and go with a transformer.
i like to build small as a can but i know i need that safe as possible power supply size weight and all.
Yours would be no bigger with a transformer...

Re: 45 line televisor

PostPosted: Fri Dec 07, 2018 10:37 am
by kd6cji
The project took a different approach. Since I obtained crater neon lamps and large regular neon lamp, I did some testing with them. I used 32 line bead disk with crater lamp and regular 32 line disk with neon. Made a 2 tube amplifier using 6AC7 and 6AG7 tubes to drive either of the lamp. As neon lamp has a smaller glowing area than the image I had to use a magnifying glass between the lamp and disk. Both versions worked fine, although picture is much brighter with bead disk and crater lamp, but crater lamp is argon-neon mixture so the tint of the picture is king of light brown rather than orange. I am planning to rebuild a driver using 6C6 and type 42 tubes, as metal tubes does not look old enough for me. Then I will need to decide which will be a final build crater or neon... And yes, I used transformers in the power supply.

Re: 45 line televisor

PostPosted: Fri Dec 07, 2018 1:23 pm
by kd6cji
IMG_2417.m4v
Video from neon lamp version
(4.34 MiB) Downloaded 183 times
Here are some pictures and short video clip. Everything is poor quality :oops:

Re: 45 line televisor

PostPosted: Fri Dec 07, 2018 5:50 pm
by Harry Dalek
Hi KD for short !
Good to see the results so far looks good me ,i would be happy .
i would enclose the lamp area and reflect the light to the disk ,but nice results it played brighter on VLC player for me ,i had another player and it did seem dim so swapped to that .

Re: 45 line televisor

PostPosted: Sat Dec 08, 2018 7:06 am
by Klaas Robers
Brown is not a light colour. Brown is dark red or dark orange. You cannot think of a lamp that gives a bright beam of brown light. But it is normal that Nipkow discs give very dim pictures. It should be that without the spinning disc, the amount of light from the light box is so huge that your eyes cannot have it. And then still the picture is a dim picture that you can only watch in a more or less darkened room.

Re: 45 line televisor

PostPosted: Sat Dec 08, 2018 6:32 pm
by gary
Klaas Robers wrote:Brown is not a light colour. Brown is dark red or dark orange. You cannot think of a lamp that gives a bright beam of brown light. But it is normal that Nipkow discs give very dim pictures. It should be that without the spinning disc, the amount of light from the light box is so huge that your eyes cannot have it. And then still the picture is a dim picture that you can only watch in a more or less darkened room.


Yes, but be aware that in this case he is using a bead disk so the light source requirement is considerably reduced (although for a disk of this size I would have thought 1/4" (6.35mm) would have been a better choice.

I find a single high brightness 5mm white LED more than adequate for daylight viewing using 3/16" (4.75mm) optical quality acrylic balls (beads) in a 9" disk.

Having said that staring into a high brightness LED is no fun ;-).

Re: 45 line televisor

PostPosted: Tue Jan 08, 2019 6:23 am
by FlyMario
Did you ever mention how big that Disk is that you are going to be spinning around 900rpm? Impressive though I wonder how it being shiny might mess up the results. That motor is cool!

Peter J. Fischel