NBTV Television Analyst

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Re: NBTV Television Analyst

Postby Harry Dalek » Fri May 01, 2020 2:15 pm

Steve Anderson wrote:
Harry Dalek wrote:I am trying to understand how you came about the idea for this...

When I was about eight I got a Meccano set for Christmas, and I still have it! (For those that know what Meccano is). All sorts of mechanical bits and pieces, I-beams, flat plates, axles, gears, nuts and bolts, even a clockwork motor! Link follows...

https://en.wikipedia.org/wiki/Meccano

Putting a circuit together is much the same, you use the appropriate part to fit what's required. That's a simplification, as often the 'magic part' you need doesn't exist, so you dream up an alternative - mechanically you'd fabricate the part you need. That often is the hardest part.

Steve A.


Best toy next to lego i got lego but wanted meccano more really ! ...yes here it is making some thing work from an idea ..you can do it from scratch i have to use your ideas and re purpose :wink:
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Re: NBTV Television Analyst

Postby Steve Anderson » Fri May 01, 2020 2:49 pm

At first I was going to ask, "What 3k3?", but guess you mean on the LED. That will make no difference, just limit the range of adjustment.

My (and not just me) thoughts are, you're simply overdriving the CRT, you're expecting too much light out of it. You could try turning the horizontal drive down to zero (but don't disconnect the CRT plates to do that). Expand the resulting vertical line to full screen. Adjust for focus and brightness as you would if it were an oscilloscope. Is that bright enough? The trace is rotated 90 degrees but that doesn't matter.

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Re: NBTV Television Analyst

Postby Harry Dalek » Fri May 01, 2020 3:00 pm

Changing the 3.3k resistor to a 10k the zener started to go into range ...

The led seems to be causing the problem when too bright !
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Re: NBTV Television Analyst

Postby Steve Anderson » Fri May 01, 2020 3:18 pm

Yep, you are in effect overdriving the CRT, all you're doing there is reducing the amount of overdrive possible. But I suggest doing the above test anyway.

Once you've got it set up in 'oscilloscope mode' without touching any other controls gently increase the horizontal drive, each line will be come dimmer.

You're spreading the light output of one line across 32. That's like reducing the aperture on a camera by 4 f-stops, say from f4 to f16, a factor of one thirty-second.

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Re: NBTV Television Analyst

Postby Harry Dalek » Fri May 01, 2020 3:33 pm

Steve Anderson wrote:At first I was going to ask, "What 3k3?", but guess you mean on the LED. That will make no difference, just limit the range of adjustment.


Sorry i got excited at the results of changing the the range of the 3.3k opto resistor i changed it to a 12k the zener is staying at 5.03v full crt brightness to 5.08v so yes it does limit the range but you are never going to use full brightness and the zener is staying put .

My (and not just me) thoughts are, you're simply overdriving the CRT, you're expecting too much light out of it.


Yes for sure i agree there ,its not needed wanted either .

You could try turning the horizontal drive down to zero (but don't disconnect the CRT plates to do that). Expand the resulting vertical line to full screen. Adjust for focus and brightness as you would if it were an oscilloscope. Is that bright enough? The trace is rotated 90 degrees but that doesn't matter.

Steve A.

[/quote]

Yes even still even with the 12k resistor still in place ! more than bright enough ....focus has always been on the full end of the wiper steve should i increase the 68k across the 1M focus trimmer its 63k i feel it needs to be bit more than that to have a center adjustment range ,
OK Steve
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Re: NBTV Television Analyst

Postby Steve Anderson » Fri May 01, 2020 3:41 pm

The specification for the optocoupler shows a spread of eight to one in the Current Transfer Ratio (CTR). This one may just be more sensitive than those used previously.

Steve A.

Right! That's put to bed!
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Re: NBTV Television Analyst

Postby Harry Dalek » Fri May 01, 2020 4:00 pm

Steve Anderson wrote:The specification for the optocoupler shows a spread of eight to one in the Current Transfer Ratio (CTR). This one may just be more sensitive than those used previously.

Steve A.

Right! That's put to bed!


Not my wiring for a change that pleases me !

Yes i did notice a slight difference in the NEC to the 2561 opto to the other batch different maker which i got more light out of the crt raster ..touchy bugger by the looks of it now i know ..

i can move on now to the rest of this project .

mid range brightness setting below
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Re: NBTV Television Analyst

Postby Steve Anderson » Fri May 01, 2020 4:41 pm

Welcome to the world of semiconductors! As an example...

A BC108 can have a current gain of between 110 and 800 under specified test conditions, if your volts, current and temperature are different the gain could be outside those limits...

Even the more recent BC548 is exactly the same...

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Re: NBTV Television Analyst

Postby Steve Anderson » Fri May 01, 2020 4:43 pm

Yep, that's looking a lot better!

I'll complete/continue the description of how this works tomorrow...

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Re: NBTV Television Analyst

Postby Harry Dalek » Fri May 01, 2020 5:37 pm

Steve Anderson wrote:Welcome to the world of semiconductors! As an example...

A BC108 can have a current gain of between 110 and 800 under specified test conditions, if your volts, current and temperature are different the gain could be outside those limits...


Arrrr i see... we had this problem at BHP with summer temperatures effecting our chemical plant always had to readjust settings to correct that ..

Even the more recent BC548 is exactly the same...


i will keep an eye from now on what the transistors gain should be ..


Yep, that's looking a lot better!

I'll complete/continue the description of how this works tomorrow...

Steve A.


I also increased the 63k by 33k to more center the focus control a bit more .

Yes please do when you feel like it explain the CRT circuit more helps me and others ..in fact this last problem pain in the arse it was was good for learning .
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: NBTV Television Analyst

Postby Steve Anderson » Sat May 02, 2020 1:30 pm

Just a short continuation....
Breakdown 8.gif
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The above replaces the current source in the previous examples with a phototransistor. As before the voltage across the phototransistor stays constant, the only thing that varies is the current through it, just as our current sources before.

This opto-coupler is a 'perfect' device (none actually exist) with a CTR (Current Transfer Ratio) of 100%. In reality they're usually much less than this, mostly less than 20%. What this means if you put a current of 5mA through the LED, the photo-transistor current will also be 5mA (in our perfect example above).

The diagram shows exactly the same as before, all we've done is added the opto-coupler, the rest of the circuit is exactly as before.

There is no electrical connection between the LED and phototransistor, the only connection is optical, I.R. the same as a remote control for a TV.

Why I.R.? Silicon is much more sensitive to I.R than visible light, so much so that at shorter wavelengths (blue) it's almost blind.

Next will be the real-world example, the CRT application within this thread. But before then, any questions? The above should be starting to look familiar...

Steve A.
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Re: NBTV Television Analyst

Postby Harry Dalek » Sat May 02, 2020 5:16 pm

Thanks Steve for the above work on the opto coupler to Hv transistor circuit explanation i will sit down after and and go over that again .
i spent most of the day looking into the heater problem
I got a little transformer that's now powering the vcr139A i tried a few things today it was the safest and best way to go about powering the heater ...for others its a 4v heater and the 3BP1 is a 6.3v heater and here since the cathode is connected to one side both shall never meet reason i couldn't use the 3bp1's Ac heater supply .

Its not to big and fits close to the large transformer

i can now go about seeing power the rest of it up .
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: NBTV Television Analyst

Postby Harry Dalek » Sat May 02, 2020 7:24 pm

I just had enough time today to hook the second CRT VCR139A up but at lower settings just running it here on -600 volts ran the devil monitor over -800 .
As expected it needs less deflection size as the 3bp1 does sharing the deflection Amplifiers so that's knocked right back for the VCR139A ..i will see if i can improve things tomorrow.
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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: NBTV Television Analyst

Postby Steve Anderson » Sun May 03, 2020 12:24 pm

That's one of the trade-offs of electrostatic CRTs (and magnetically deflected CTRs too), as you raise the tube voltage the brightness gets better, the focus sharper, the downside is the deflection requires more drive and to an extent the grid too. Using two different CRTs within the same device further complicates matters with all the different voltages required, it can be done of course, it just makes things a bit more complex.

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Re: NBTV Television Analyst

Postby Harry Dalek » Sun May 03, 2020 3:24 pm

Steve Anderson wrote:That's one of the trade-offs of electrostatic CRTs (and magnetically deflected CTRs too), as you raise the tube voltage the brightness gets better, the focus sharper, the downside is the deflection requires more drive and to an extent the grid too. Using two different CRTs within the same device further complicates matters with all the different voltages required, it can be done of course, it just makes things a bit more complex.

Steve A.


Yes for sure Steve would be much easier to go down the road of using the same CRT as far as voltages and deflection side needing different levels , i agree its all still possible but as you say makes it a touch harder ...

Well i have never tried this before so its another tick for the to do list and i have Tried where possible till i got to this have to wait and see point made the project cope with the coming problems ...

I was tossing up from the start to use 2 identical deflection amplifiers for each tube but i was originally going with 2 3BP1's so i was thinking this was pointless just more circuit's and i wanted the 2 crts to mimic each other anyway ...i think it can still be done i will see i can drop the ramp levels just for its deflection plates ...

I will increase the HV negative to its correct working data levels and see how it go's ...boy this CRT is sensitive perhaps at these levels i noticed just tuning the tube i moved the raster down a touch ...can the earths magnetic field effect the tube ?

Today i just mounted some panel control's and such so i can neaten some wiring up then i can just work on the second CRT see how it go's worst case i can always swap back to the 3Bp1 but i will give the VCR139A a go for now.
The DVD player never looked so good 8) made more use of the empty case space than the dvd player this lay out for CRT monitors really seems much better than the standard L shape case if any one out there is thinking of a case for their crts ...transformers placement is less of a problem but i will see if it effects this send crt it is a bit closer and pretty much rotated right around to what i did on the Binocular 2 crt build .
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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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