Valve Baird Televisor circuits for Marcus et. al.

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Postby chris_vk3aml » Fri May 09, 2008 7:20 pm

The "boss" or "flanged bushing" that you require depends on the shaft diameter of your motor. Many of the fractional horsepower motors that I've come across in the last 35 years have had a shaft of approximately the old 1/4 inch diameter. These form a snug fit with either:

(1) Radio control knobs - these generally include two grub screws for fastening.

(2) Flanged bushing from an old variable capacitor from a radio transmitter or receiver.

You can also find some flat gears that have similar grub screw fastenings. Generally, the relatively slow rotational speed you're contemplating - less that 800 rpm - will not demand any sort of dynamic balancing of the bushing, though careful centering of the scanning disc is desirable.

No hard and fast answers here, but you should be able to adapt something fairly readily.

If all that fails, you could have a suitable flanged bush run up at moderate cost by someone with metal lathe shop skills. Starting with a lump of brass would be the easiest and cleanest-cutting metal to use.

Hope this helps,

Chris Long VK3AML.
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Postby Marcus » Sat May 10, 2008 12:29 am

I think have found a solution... Maybe,

I was reading here about salvaging suitable bearings to run discs from a VCR, I pulled a drum out of an old VCR we had lying around. It looks like it could be modified a few ways to make a suitable hub or 'boss'.
The 12v fan motor I have looks like it would fit into it directly, but the 12v drill motor I salvaged has a much smaller diameter shaft.
I guess i'll just play around with it to see what works better when the disc comes.
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Postby chris_vk3aml » Sun May 11, 2008 12:43 am

Hello again Marcus et al,

Here are two more complete Nipkow disc TV receiver circuits of American origin from the period around 1930.

One is from "The Radio Manual" by George E Sterling (D Van Nostrand and Company, New York, 2nd edition, September 1929) p 620. It was designed for 48 or 60 line reception at 16-20 frames/sec. The 30 Henry choke coupling to the neon is really not to be recommended. Apart from being heavy and bulky, these audio chokes have to carry a fair amount of current, and their self-capacity would limit the high frequency response of the system.

The other two circuits are from "Radio Physics Course" by Alfred A Ghirardi (Radio and Technical Publishing Company, New York, 1933 printing) pps 865-867. These two diagrams relate to the same receiver system. If you want photos of the electronics and the mechanical scanner associated with these, I can scan and post it, but I thought the circuit diagrams would be more valuable to you at the design stage.

Hoping - as always - that this helps,

Best wishes to everyone,

Chris Long VK3AML.
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Postby chris_vk3aml » Sun May 11, 2008 1:52 am

More circuits - this time from (I think) the 1930 edition of Moseley and Barton Chapple's "Television Today and Tomorrow" (Pitman's, London) showing the British style of Nipkow disc TV receiver design. I would guess that the "dual receiver" would be the design evolved for the last of the "Noah's Ark" Televisors, after the advent of the dual sound-and-picture Broadcasts over two BBC medium wave transmitters in March 1930.

More grist to the mill!

All the best,

Chris Long VK3AML.
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Postby Marcus » Sat May 17, 2008 5:39 pm

I found a good little chassis for the video amp in my junk cupboard.
I was wondering is if I place the motor within an inch of one of the video amp valves on the chassis will it create hum in the circuit?
It will be running of it's own 12v power supply but will be in close proximity to the valves.
Another thing I have been thinking about is providing DC power for the 12v motor without using silicone rectifiers. I have a few 6X5-GT valves that I thought would do the trick, but I'm not sure that one of them could supply enough current to run the motor even at 12v.
I might give it a go and see what happens.
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Postby chris_vk3aml » Mon May 19, 2008 2:43 am

Yeah Marcus, that should be OK with a dc motor - depends a bit on the level at which the valve's working but if it's near an output valve working at high level it should cause no problem by the motor's proximity.

Further to my earlier posting about the home-made neons, I found my photo of the late Gil Miles, former NBTVA President (in profile) holding the trial TV neon made from the envelope of an old QQVO6/40 valve. I described this in a posting under this subject heading on (I think) 7th May. This photo was taken on the occasion of Miles' presentation of his replica Nipkow scanner of 1929 to the Melbourne (Australia) Science Museum (now Museum Victoria) early in 1972.

He is explaining the problems with that neon to the executives of the Museum in this picture.

I also am posting a silhouette photo of the TV neon surviving in the valve collection of the Powerhouse Museum in Sydney, Australia - a photo I took in 1980 with the assistance of then-curator Jeff Sergel.

All the best,

Chris Long VK3AML.
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Postby chris_vk3aml » Mon May 19, 2008 8:28 pm

Hi Marcus:

Here's another view of Baird's "phonic wheel" synchroniser, in case you're curious about the original form that this synchroniser took. It was based on a nineteenth century design, originally - I believe - used as part of a multiplex telegraphy system by the French (?) experimenter La Cour sometime prior to 1880.

You'll note that the number of teeth on the cogwheel = number of lines per picture = number of holes in single-spiral scanning disc.

The original Baird phonic cogwheels were laminated, in the same manner as a transformer's laminated core, and for the same reason - reducing the flow of eddy currents within the metal, opposing the buildup of the magnetic field. Each of the stampings was electrically insulated from its neighbour by the chemical treatment of the laminations. In a low-tech home-made cogwheel, this insulation might take the form of nothing more high-tech than a thin layer of wax, shellac or thinned estapol.

For the amateur, the cogwheel is a difficult device to make, really demanding the facilities of a metalworking lathe.

The connection of each magnetic pole-peice within the magnet windings with a frame of magnetic material (eg mild steel) is important, as the two pole pieces, the clamping frame and the cogwheel have to form "a magnetic circuit".

All the best,

Chris Long VK3AML.
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Postby Marcus » Mon May 19, 2008 11:05 pm

Thanks Chris,
I still like the thought of the phonic wheel, but for now I'll keep it simple and do without it. I think I need a better work area than my study and a lathe before I attempt to make one.

I received my Nipkow disc from Vic today along with two 100e1 neon regulator valves which I bought in a tube lot along with some dekatron counter tubes. I fired them up and they have a nice orange/pink glow about them. I'm not sure if they will be bright enough but I will give them a go behind the wheel and see how it looks.
Here is the data sheet if you are interested; http://tubes.mkdw.net/sheets/030/1/100E1.pdf

If they are no good I still have the little indicator neons on their way and I'll make an array out of those. I bought an old valve AM radio of ebay this week too, so with any luck I can get this thing operational in the next couple of weeks.
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Postby chris_vk3aml » Mon May 19, 2008 11:16 pm

OK great about the progress, Marcus!

One thing that you could try with the "Nixie" tubes is to reverse the voltage applied to them, so that the backing anode mesh glows, rather than the alphanumeric figures. That sometimes produces more light, and more evenly distributed light.

Don't forget that these glow discharge neons need a series current limiting resistor if you're going to apply high voltage to them. When they're in the anode circuit of a valve, the static anode resistance of the valve generally provides the current limiting effect, but if you apply high voltage to a neon WITHOUT a series current liming resistor, STAND BACK!

All the best,

Chris Long VK3AML. (I think I have Mike VK3BHM vaguely interested in our 160 metre plans also!)
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Postby Marcus » Mon May 19, 2008 11:37 pm

Whoops!
I didn't use a limiting resistor when I tested the neon earlier this evening. I've probably shortened it's life span a little but it was only on for a short period of time. It did actually feel a little warm!
I hadn't thought of a nixie. I actually have a few lying around and have on occasion managed to get the effect you are talking about by shorting out the wrong lead/s.

Thats great that you managed to rope in another guinea pig for the 160 meter experiment. It will be interesting to see what results we get.
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Postby Marcus » Sun May 25, 2008 6:50 pm

I have posted pictures of the neon regulator tubes I bought and their glow. Has anyone tried these as a light source?
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Postby Klaas Robers » Mon Jun 02, 2008 5:13 am

I tried a somewhat different type in the beginning, but was very disappointed by the very low light output. This is absolutely nothing compared to even ONE high brightness LED.

On the other hand the Neon Tube changes its light pattern when the current goes under a certain value. Then parts of the tube extinguishes giving a very uneven light distribution.

So I switched to 30 HiBri LEDs. in one long chain, that simply replace the neon lamp.
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