NBTV Television Analyst

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Re: NBTV Television Analyst

Postby Harry Dalek » Sun May 03, 2020 6:14 pm

Running the VCR139A at now -845v its much improved video below i was using the same 10k brightness control but different resistor values for the wiper so sightly different cut off positions just a test the vcr139A is giving the same results on the 5v zener as in changing voltage so i will increase the resistor again on the wiper . the deflection is more evened out now but ran out of time today to do any more ..

Still have to even out the deflection amplifiers but getting there ...

Any case pretty pleased with todays work and results .There you go Andrew another 2 of the crts live !


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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 » Mon May 04, 2020 2:36 pm

Concluding this deconstruction of the CRT grid-drive circuit...

Here's the final circuit much as built on the left, Harry's voltages are slightly higher so currents will also be slightly higher too, but the principal is the same.

Breakdown 9.gif
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The above should be familiar...the resistors and pot for the focus has been simplified into a single resistor as before. (Right above).

Next we add +1400V to the voltages in red, this makes it easier to understand when dealing with positive voltages (Left below)...then get rid of the resistor(s) between the +80V point and +1400V. (Right below).

Breakdown 10.gif
Breakdown 10.gif (12.83 KiB) Viewed 1370 times


....and really that's it! The right hand sketch should be very familiar to what has been covered before. The voltages and currents might be different, but the workings are just the same.

There will be more on this which goes into other aspects where this circuit could be improved, but let's take a break for a while.

In pulling this to bits what tools have we used? Basic arithmetic (I'm not going to even call it Math), add, subtract, multiply and divide, plus Ohms Law which uses so far just those four 'tools'. No long-winded algebra, no calculus, nothing 'exotic' at all. The biggest task is finding the bits that 'fit' and work together as you wish. The design was/is just the reverse of what has been done here.

Steve A.

Postscript: What's R905 for? Any guesses? It's not an easy nor obvious answer! Remember, the CRT grid should not go positive so there's no current in R905, therefore no voltage drop across it. So why is it there? Hint: and a rather obscure one...R905 should be mounted right on the CRT socket pin, really close to the CRT, preferably within 1cm, I should have mentioned this before, but it 'slipped through the cracks'.
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Re: NBTV Television Analyst

Postby Harry Dalek » Mon May 04, 2020 4:35 pm

Steve Anderson wrote:
Postscript: What's R905 for? Any guesses? It's not an easy nor obvious answer! Remember, the CRT grid should not go positive so there's no current in R905, therefore no voltage drop across it. So why is it there? Hint: and a rather obscure one...R905 should be mounted right on the CRT socket pin, really close to the CRT, preferably within 1cm, I should have mentioned this before, but it 'slipped through the cracks'.



One again thank you Steve for that post ...mmmm it should be mounted right on the G1 ! OH as to why it should be mounted right on the CRT pin is a bit a of head scratching ...arrrrr i am no good at this !
We are control grid modulating this here i can only think any thing where a part has to be mounted right on a pin like that has to do with noise pick up ..but the wiring at the other end might give the same problem unless the whole circuit was mounted on the crt pin Base ,i have noticed on some CRTs the video amplifier transistor its little board was on the CRT pin base ...

Boy i am not sure why it is there or why 1k as you say there's no real voltage drop apart from 0.19 before and 018 after bugger all on end of the optocoupler
adjustment ,i was thinking perhaps keeping the tube if it was set up for video modulation keep it from over modulating the tube ...

But it will be interesting to find out the real answer !
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 » Mon May 04, 2020 4:53 pm

Good guess Harry, but not correct sadly. I'll keep you in suspense until the same time tomorrow in case someone else fancies a go at it.

Yes, often the video amplifier(s) are on a small PCB mounted on the CRT socket. In standard 625/525 TV the bandwidth goes up to 5-6MHz, you don't want long dangling leads with all that capacitance rolling off the high frequencies (picture detail). But here we're well under 20kHz at around 10kHz really, basically 'special audio' so that's not the reason for R905. Nor pick-up from the rest of the device, though you should try and prevent that.

Steve A.
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Re: NBTV Television Analyst

Postby Steve Anderson » Mon May 04, 2020 6:43 pm

One thing I have omitted, is that this is an example of a Grounded Base (sometimes called a Common Base stage, which is arguably more accurate). The base stays at a constant voltage, while the emitter is used as the input and the output is extracted from the collector.

Not only, but also, it's a form of a Cascode stage, often used where gain is required at high frequencies, RF and IF stages. Usually two NPN or PNP bipolar devices, or two N or P-channel FETs/MOSFETs, or two high-frequency valves/tubes. Though here obviously this is not a high-frequency application, it simply fits and meets the brief.

The rather odd thing here is we're using a PNP transistor with an NPN photodiode, they're usually of the same polarity (with valves/tubes they have to be). But there's no base connection in the phototransistor so as long as it conducts current, the tranny will respond and doesn't care.

Steve A.
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Re: NBTV Television Analyst

Postby Harry Dalek » Mon May 04, 2020 10:26 pm

Steve Anderson wrote:
The rather odd thing here is we're using a PNP transistor with an NPN photodiode, they're usually of the same polarity (with valves/tubes they have to be). But there's no base connection in the phototransistor so as long as it conducts current, the tranny will respond and doesn't care.

Steve A.


Yes this really confused me but explaining it here it does make sense of cause ...
Its a very good design i clap my hands its beautiful ...! to design something for low voltages is one thing but to do this for voltages at 1.5 kv had it up over 1.6 kv it may be easy for you Steve but its some thing not in me and most of us out there !
i can just like a kid following a lego plan just try and not to make a mistake in the design ...i like remaking this as i trust it and every time i do i learn a little more...the problems i have had this time were good for for me even if would i rather none .. it did force me to think hard what was going on .

Little more work on the CRTs i will move onto the PMT side but one problem at a time so far i am pleased i have gotten to this stage :wink:
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 » Tue May 05, 2020 5:59 pm

OK, R905? Why is it there?

Have a look at the following...

CRT vs Tetrode 1.gif
CRT vs Tetrode 1.gif (8.01 KiB) Viewed 1329 times

See any real difference?

Now, forget the deflection plates, they don't (or shouldn't) intercept the electron beam, hence that's why they're 'dotted out'. What have we got left? Basically, in this case, a tetrode. Tetrodes, like triodes and pentodes have gain or amplification. The names of each electrode may be different, but that really is of no consequence. Electrons don't care what you call each electrode, they just do what comes naturally to them.

How do we make an oscillator? We deliberately feed back some phase-shifted part of the output back into the input. Here we don't want or need that.

Rather than bang out a long diatribe, i'll refer you to this site, it's aimed at guitar amplifiers, but applies to all amplifiers whether valve/tube or semiconductors...including ours here...

https://www.aikenamps.com/index.php/gri ... -they-used

You may see these little innocuous resistors dotted around all sorts of amplifiers, they cost almost nothing yet keep things behaving as they should.

Steve A.
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Re: NBTV Television Analyst

Postby Steve Anderson » Tue May 05, 2020 6:40 pm

One of the big differences of CRTs and other tubes is the actual shape and positioning within the glass envelope of grids and anodes. Have look at the following two diagrams..

Generic Internals 1.jpg
Generic Internals 1.jpg (36.95 KiB) Viewed 1326 times


Very different layouts, but one is aimed at gain, the other more towards display observation. Whatever, both can be amplifiers, therefore oscillators, here we do not want that!.

Steve A.
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Re: NBTV Television Analyst

Postby Harry Dalek » Tue May 05, 2020 9:06 pm

Yes Steve i see the lay out of a vacuum tube and a CRT same same apart from size and positioning of its control grids anode..
Great diagrams btw nothing like an image to explain something .

Yes site was very good in explaining the grid resistor ,that will be on my mind as to why they are there now on these circuits ,i will see about adding the resistor right of the CRT pin not a big problem .

But yep i didn't know about this till today ...may be if i worked on more vacuum tube projects i might of picked this up ...now i know :!:

Have not worked on the project today i had to work today ..but my mind was on a step ahead the PMT ..before i used my power supply to control the voltage in 200v steps but i might look into the gain control variable resistor this time ..i know these things are fussy depending on the light its getting i will need some control here least the light from the CRT can also be controlled so .. factors its supply voltage the light intensity ..always best to run a PMT from the low voltage end and work up to the wanted results .
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 » Wed May 06, 2020 3:58 pm

Ok steve ...i will do a new post
Last edited by Harry Dalek on Wed May 06, 2020 8:00 pm, edited 3 times in total.
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 » Wed May 06, 2020 7:19 pm

Harry, sorry to p**s on your parade, but please stop using animated gifs...they're annoying to say the least and simply don't give one time to take in the picture. I remember Andrew admonishing one member who had an animated avitar, likewise it was annoying. It's much better to upload 36 pictures than six animated GIFs of six pictures each. If you want to upload a video, upload a video, please not an animated gif. If you run out of upload space (the 20MB limit here) simply post a follow-on...

Sorry Harry, but I'm sure I'm not the only one who thinks the same...

Steve A.

P.S. I think the maximum amount of attachments per posting is 50, as long as the combined total is less than 20MB. I'll not delete the above postings though I'm sorely tempted to..
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Re: NBTV Television Analyst

Postby Steve Anderson » Wed May 06, 2020 7:58 pm

Thanks Harry, just post the static photos that are pertinent to the subject matter, that's all that's needed.

"Simplicity is the elegance of design", which includes getting your message across here..

Steve A.
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Re: NBTV Television Analyst

Postby Harry Dalek » Wed May 06, 2020 8:35 pm

Steve Anderson wrote:Thanks Harry, just post the static photos that are pertinent subject matter, that's all that's needed.

"Simplicity is the elegance of design", which includes getting your message across here..

Steve A.


No problems Steve ....
As i was saying i have a few PMT tubes to choose from The Hamamatsu R1282 i just found data for pages 38 ..39 the pinouts
HamamatsuPhotomultiplierTubes.pdf
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DSCN6505.JPG


Next with 3 numbers 9524D 9252 and also 92521
DSCN6510.JPG


Also an Emi 9524 could be same as also or a replacement ...i used one of these before in the earlier PMT camera idea
DSCN6515.JPG


Last a EMI D151B ...painted Black keep out the light from the sides and back i suppose done by the past owner of the PMT


EMI_Photomultiplier_Tubes_1970.pdf
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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 » Wed May 06, 2020 8:59 pm

OK Harry, that's enough. Now follow up this as to how you intend to use it...remember no bright (daylight) exposure whilst energised....

Steve A.
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Re: NBTV Television Analyst

Postby Harry Dalek » Wed May 06, 2020 10:21 pm

Steve Anderson wrote:OK Harry, that's enough. Now follow up this as to how you intend to use it...remember no bright (daylight) exposure whilst energised....

Steve A.


As far as placement I really have a few ways i can go as in room ...depends on if the magnetic field of the transformer effects either the CRT or PMT direct facing or mirror reflecting at around 45 or so degrees so at the moment before any testing i am just guessing till i view results .
DSCN6524.JPG
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DSCN6526.JPG
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All this is still a bit off i think i would have to run the tube in for a while lower the dark current as i recall from the first go at it .
update EMI 9524
DSCN6528.JPG
DSCN6528.JPG (214.19 KiB) Viewed 1274 times

Yes i have to block up holes in its case most of that will be mounting sockets and more controls .
Any case still a bit more to do before the PMT gets tested ....i have made up my mind as shown i am using the EMI 9524 since i am more familiar with it .
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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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Harry Dalek
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