For those old f**ts amongst us...

Forum for discussion of narrow-bandwidth mechanical television

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For those old f**ts amongst us...

Postby Steve Anderson » Fri Apr 20, 2007 6:34 pm

Gents,

..don't worry, I include myself as an 'Old f**t',

Attached is a PDF of the 'Wireless World' magazine of April 1961. '50 years of progress'. There are several references to the early days of television that might be food for thought. Both the Baird 30-line system and the 405 (UK only) system.

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In addition...

Postby Steve Anderson » Fri Apr 20, 2007 7:00 pm

Gents,

Here's the first page from a 'Wireless World' publication in July 1937. It's not mechanical TV, but as can be seen the move was in the direction of electronic TV.

I have the full series, if anyone is interested in these early days of TV I'll zip them and post them here...

You'll notice there is no reference to Silicon, or Germanium for that matter. Also note that condenser = capacitor.

Steve A.
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Wireless World.

Postby Stephen » Sat Apr 21, 2007 3:35 am

Ahh, the good old days when a capacitor was still a condenser. I just love the elegant simplicity of the old valve circuitry. By the way, Mullard developed the TSP4 pentode valve that this receiver uses specifically for television. It has a very high transconductance for its time - 4.73 mA/V. I have attached the specification sheet for others like myself that appreciate the old valves.

Thanks for posting this, Steve. I for one would like to see the full series.
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TSP4 RF/IF/Video Output Valve
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Re: Wireless World.

Postby Viewmaster » Sat Apr 21, 2007 4:41 am

Stephen wrote:Ahh, the good old days when a capacitor was still a condenser.

...and when a hertz was a descriptive cycle and when a radio was still a wireless.
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Re: In addition...

Postby Phil Hunter » Sat Apr 21, 2007 6:21 am

I Have the full series, if anyone is interested in these early days of TV I'll zip them and post them here...

Yes please - I'd love to see them

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Wireless World TV

Postby Steve Anderson » Sat Apr 21, 2007 3:05 pm

OK Gents...

Here 'tis...

Steve A.

P.S. I have more TV related stuff from about the same era, all non-mechanical and (heavens forbid) some of it is American!

P.P.S. I also have a moderate databases of valve/tube stuff, but be forewarned, it's nearly 2Gb!
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NBTV CRT Monitor.

Postby Steve Anderson » Sat Apr 21, 2007 5:51 pm

Gents,

Here's a couple of pictures of a non-mechanical NBTV monitor I built about four years ago. It's a hybrid and uses both valves/tubes, a CRT and a couple of simple op-amp chips.

The full details were published in the newsletter sometime in 2003 I think.

The front view shows the need for Gamma correction when using a CRT as the signal was an equal eight-step ramp.

If anyone wants more data, just let me know.

Steve A.
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Postby DODGER » Mon Apr 23, 2007 6:03 am

Hi Steve, I would be very interested in any data/info on non-mech nbtv monitors,I have been trying to design my own one to demonstrate the historical progression from nipkow disc to crt ,thusfar I have only been able generate a nice raster on a 3bp1 scope tube and some "e"series valves for sawtooth gen and x/y plate amps. The rest is causing much head scratching . thanks Dan
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CRT Displays.

Postby Steve Anderson » Mon Apr 23, 2007 1:08 pm

Hi Dan,

Quite happy to help as I have an interest in CRTs, primarily the electrostaticly deflected versions such as the 3BP1. However, I don't want to upset those here whose interest in in the mechanical side of TV, so with their indulgence I'll continue.

I have just looked up the datasheets I have for the 3BP1...wow, it needs quite a lot of volts for a 3" tube!

So do you have any data/schematics of what you have built/modified so far? What valves/tubes from the 'e' series are you hoping to use? Do you want this display to work only with the Baird/NBTV signals? Or others as well?

As an aside, I have a DH3-91 CRT (1CP1 in the US) which one day I intend to use for a NBTV display. It's a dinky little thing, only 1" in diameter. See JPG.

Steve A.
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Postby DODGER » Tue Apr 24, 2007 2:07 am

The set-up goes ,an old homebrew scope that I found so no data on that,the scope itself gives the eht ,four screened leads bring the x and y plates to the outside world these are connected to two ECC81s wired as push/pull amps fed by two EF80s in miller transitron type style. but thats as far as i have got,how i was going to modulate the beam or keep it all in sync has still to be thought out.so any help would be greatfully received,Its to display 32/30 line images I dont think this will upset"mechanical"nbtvers as this is just another aspect of this facinating hobby. thanks dan
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Another narrow band system.

Postby Stephen » Tue Apr 24, 2007 2:38 am

This discussion, as especially the "need" to modulate the CRT beam, reminds me of another early cathode ray scanning system. Manfred Baron Von Ardenne demonstrated a fascinating television system in 1931 that utilises velocity modulation. The system modulates the apparent intensity of the raster by changing the velocity of the beam. That is, when the beam moves slowly, the raster is almost white, whereas when it moves rapidly it is almost black. This allowed the use of gas-filled CRTs that operate on low anode potentials. It is not possible to intensity modulate the beams of these CRTs.

The interesting thing about the velocity modulation system is that the receiver uses the modulation signal to deflect the beam horizontally and vertically. The horizontal and vertical deflection plates have appropriately sized capacitors across them as well as valves biased to cutoff. The capacitors receive the modulation signal through appropriately sized resistors, which charges the capacitors and deflects the beam with a velocity proportional to amplitude. When the potential on the capacitors exceeds the valve cutoff bias, the capacitor discharges through the valve and the scan starts over.

Of course, this scheme has a non-constant line rate and frame rate. There was also a modified velocity modulation scheme that used a constant frame rate with a variable velocity modulation line rate for compatibility with motion picture film.
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Reverse Engineering.

Postby Steve Anderson » Tue Apr 24, 2007 12:52 pm

Dan,

I think I would start by reverse engineering this home-brew scope, i.e. take the covers off (if any) and try to get the circuit down on paper. This takes time and patience. Often it's hard to make sense of what you find!

Assuming that it works, power it up and make some voltage measurements, be careful as this 3BP1 tube is designed to be used at final anode voltages of 1500-2000V, although it might be possible to use lower voltages.

I have attached one of the datasheets I have for this tube which might help if you have no info.

Steve A.
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Postby DODGER » Wed Apr 25, 2007 9:10 pm

Hi Steve,
I do appreciate the info on 3bp1 it has given me much food for thought.I spent much of yesterday pouring over old text books and copys of practical television to try and gleen asmuch as I can about scopes and the hight potantials involved.
I will go on with this project slowly and carefuly.
Yes I agree, reverse engieering is the way to go here,today Ill take measurements, jot down diagrams and maybe a few pics to help me recycle the parts of the scope into an"ALL- ELECRIC" visor...
Also I would like to post a picture of a Baird signal(taken in 1935) on a crt,will this cause copyright problems?
thanks Dan
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More data.

Postby Steve Anderson » Wed Apr 25, 2007 9:55 pm

Dan,

Just as a help (I hope) here attacted are two datasheets, one for the ECC81 and also the EF80 if you don't have any info to hand.

They at least will enable you to identify which pin is what. Remember the pin numbers are from the underside of the tube, counting clockwise. As opposide to chips which are counted counter-clockwise from above. Which actually amounts to the same thing.

As for the copyright issue, I doubt there's a problem, a lot of time has gone by. Others willing to put their oar in on this?

Steve A.
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Postby DODGER » Tue May 08, 2007 8:28 am

HI STEVE, thanks for ef80 and eccback i made 81 info, i haven,t posted for a while as i,ve been making a careful study of scopes set up{and others}to make sure i know where dangers lie and of course just how c.r.t.s actually work. the scope is now skeletal i.e just tube and power supplies {bleeder etc} but now i,ve got a problem, i cannot focus the spot to smaller than the size of a pea, could this be because the x y plates are connected to nothing? i,ve only done brief tests so as not to damage anything. sometime back i made a nipkow disc camera /monitor to the nbtva design which gives good results on "Gary Millards big picture" on the family pc, but unfortunately thats fixed to where it is! a small green screen type monitor dressed to look"1930s" would be very handy for demonstrations. Here also is a pic of a baird signbal as promised, i hope it doesn,t come down an odd size! many thanks. dan.
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