Narrow-Bandwidth Television Association

Progress indeed Harry...I'll leave you get on with it...

178k is near enough, even 170-190k should be fine. Don't forget that multimeters on the resistance ranges are less accurate than on voltage, plus it may need calibrating - but few do that. A 1% resistor is more than likely to be more accurate than the meter.

Just because things may be 'digital' it doesn't mean they're accurate. e.g. A DS18B20 direct-to-digital thermometer has a resolution of 1/16 of a degree Celcius. If it's saying the temperature is 20.0000 degrees and it gets slightly warmer it outputs 20.0625 degrees. But the accuracy is +/-0.5 degrees. It actually could be anywhere, say 20.4375 degrees.

So when matching components, it's usually not the precise value that's important, but they read as close as required.

Steve A.

Steve Anderson wrote:Progress indeed Harry...I'll leave you get on with it...

178k is near enough, even 170-190k should be fine. Don't forget that multimeters on the resistance ranges are less accurate than on voltage, plus it may need calibrating - but few do that. A 1% resistor is more than likely to be more accurate than the meter.

Just because things may be 'digital' it doesn't mean they're accurate. e.g. A DS18B20 direct-to-digital thermometer has a resolution of 1/16 of a degree Celcius. If it's saying the temperature is 20.0000 degrees and it gets slightly warmer it outputs 20.0625 degrees. But the accuracy is +/-0.5 degrees. It actually could be anywhere, say 20.4375 degrees.

So when matching components, it's usually not the precise value that's important, but they read as close as required.

Steve A.

Yes Steve as i have had some time today half finished the sawtooth circuits i will post up any results when done .

I try to match parts best i can find it is hard to even find a 1k resistor that is 1k most of my parts are 5 10% types

ON multi meters i have two the same model i some how think one has a improved board on it has a massive DC voltage range that would kill most multi meters
I have had it up to 1600 volts no problems the other same model gos off range over 500 volts ..both i could not do the amp reading but a 3rd different model worked fine ...also to find the same reading on all meters its always close but never 100% the same .
I suppose with these things you get what you pay for but they are still great for the price .

Harry Dalek wrote: ...to find the same reading on all meters its always close but never 100% the same .

There's an old saying in horology (the study of timekeeping), "A man with one clock always knows what the time is, the man with two clocks is never sure."

Steve A.

Steve Anderson wrote:There's an old saying in horology (the study of timekeeping), "A man with one clock always knows what the time is, the man with two clocks is never sure."

Steve A.

Very True and how the universe works really time is never the same for any thing that exists ..

Today i finished off my saw tooth circuits pretty much to Steve's circuit below...i used Tl082 and i didn't use well not yet R708 or R728 run as is ....the line scan is set to the minimum size setting for this small CRT .....raster just fits it is to large for the higher control settings so to keep raster size controls in range for this CRT , i would say those resistors should be put in ...values i will have to test with my trusty resistor wheel .
Running here at 32 line for testing today

youtu.be/r3xYr4tcmmw
Saw tooth Photos below
First photo the line scan sawtooth 5 volts per div the gif is same setting frame sawtooth out of the TL082 .
The spread out scan was the first scan i saw on this tube after some adjustments some thing a little better for this CRT

Yep, as I expected, you'll have to add those two resistors otherwise as you see you've got a bit too much deflection. Let us know what values you end up fitting and I'll add them to the circuits for future reference. They may not be the same value...

Steve A.

Steve Anderson wrote:Yep, as I expected, you'll have to add those two resistors otherwise as you see you've got a bit too much deflection. Let us know what values you end up fitting and I'll add them to the circuits for future reference. They may not be the same value...

Steve A.

Well Steve it does just work for some thing much smaller to the CRT size of the last one but thats pretty good on your design ..Yep i will add the those resistors and get the trimmer resistors back in range .

as you can see when i first got it going there was a fair bit of scanning way past the screen last photo back in range ....just ....

As a starting point make the resistors equal to the 'size' pot value, than adjust as (if) required.

You may find you'll have to do the same with the 'position' pots too - see how it goes.

Steve A.

Steve Anderson wrote:As a starting point make the resistors equal to the 'size' pot value, than adjust as (if) required.

You may find you'll have to do the same with the 'position' pots too - see how it goes.

Steve A.

Hi Steve i did end up trying this today using 10k resistors seems fine for size controls and position seems ok as is
You tube video adjusting the size position controls .

youtu.be/mbrr8DlRV3g

I have just finished the video sync detection circuit much easier build on the larger board have not tested it yet ..looking at rest of the project parts pretty much have it all .
I ended up using the values in Blue .

i may as well test at 32 line and change to my wanted ideas after i see the video display side of it works

More progress. The 'position' controls are a little one-sided, but you can centre it so leave it as is for now, you can come back later if you wish and do it.

Now you have the deflection amps working you should be able to get a better focus by adjusting the focus and asitig contols, if not let me know. Remember this is an older design of tube so it's not going to be quite as sharp as the 3BP1, it's also running at a much lower voltage.

Adjust the 'bias' pots pots in each deflection amp so the ramp waveforms at the collectors of the output transistors are centred around +180V or thereabouts with the raster centred. They probably won't be exactly equal, a few volts either way shouldn't make any difference. Then twiddle the focus/astig pots. Turn the brightness down a way, these older tubes were not that bright, nowhere near what you may be used to. Setting them too bright leads to de-focusing which can't be fixed. Remember modern 'scope CRT tubes run on many kVs, sometimes up to 15kV - not just 900V.

Steve A.

Steve Anderson wrote:More progress. The 'position' controls are a little one-sided, but you can centre it so leave it as is for now, you can come back later if you wish and do it.

Yes a little more deflection on one side of the position control ,i feel as long as you can center the raster that is fine with me ,i am not to bothered with evening them out that much ,it has a pretty wide movement as is .

Now you have the deflection amps working you should be able to get a better focus by adjusting the focus and asitig contols, if not let me know. Remember this is an older design of tube so it's not going to be quite as sharp as the 3BP1, it's also running at a much lower voltage.

i was reading passed posts i think i recall others perhaps you saying touching the screen on this older CRT design it can put it out of focus ..
I forgot to readjust the Focus and Astig controls i will try adjusting it again .

Adjust the 'bias' pots pots in each deflection amp so the ramp waveforms at the collectors of the output transistors are centred around +180V or thereabouts with the raster centred. They probably won't be exactly equal, a few volts either way shouldn't make any difference. Then twiddle the focus/astig pots. Turn the brightness down a way, these older tubes were not that bright, nowhere near what you may be used to. Setting them too bright leads to de-focusing which can't be fixed. Remember modern 'scope CRT tubes run on many kVs, sometimes up to 15kV - not just 900V.

Steve A.

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I will give that procedure Steve a go thanks , bit busy tomorrow also but with a bit of luck may make it to the shed ..
I have noticed brightness control does effect focus well it did when i first got the tube going ,i will also have a look at that again .
It sounds like you have to treat or adjust this type of CRT a little differently ...thats ok it is what it is it will be interesting to see how far its worth going with number of lines with this one ...
If any thing 2nd go here for a NBTV one i am finding easier sure does help knowing what not to do again ! Its also easier using bigger boards cuts down on wiring board circuits to together with plastic coated wires makes it neater .

The brightness will affect the focus, I suspect you've got it too high. These are pre-WWII designs and had to be viewed in 'subdued lighting', much like the early TV CRTs. Normal interior household light is far too bright. Pull the curtains, drop the blinds, turn the brightness down and you'll get far better results. How old are these tubes? No surprise really. Think of dimly lit research labs....

Even the comparatively modern (50s?) DG7-32 3" CRT I have used in the past was far better in low ambient light.

Steve A.

Steve Anderson wrote:The brightness will affect the focus, I suspect you've got it too high. These are pre-WWII designs and had to be viewed in 'subdued lighting', much like the early TV CRTs. Normal interior household light is far too bright. Pull the curtains, drop the blinds, turn the brightness down and you'll get far better results. How old are these tubes? No surprise really. Think of dimly lit research labs....

Even the comparatively modern (50s?) DG7-32 3" CRT I have used in the past was far better in low ambient light.

Steve A.

Ok i will knock the brightness control back and see ,i am interested to see how the focus gos , i will also touch the screen or hand close i have read this effects trace .
This VCR139A Number 2845 of how many made ? its made for the army so a lesser grade CRT i have read ...wonder what the army they used them for made WWII or before so at least in its late 70's ...its great they still look new and work as new ...i am trying to be kind to it its had a long rest between tests

These early tubes were susceptible trace movement/distortion when you touched the screen. Later tubes have a very thin layer of Aluminium deposited on the inside of the glass. This stops the electrostatic deflection caused by your hand/body which is (or should be) near ground/earth potential.

On some datasheets you may notice a word similar to 'Aluminiumised', that refers to this process that has been applied to the tube. A side effect is that in some tubes it reflects light from the rear of the phosphor forwards making the trace a bit brighter.

Steve A.

Steve Anderson wrote:These early tubes were susceptible trace movement/distortion when you touched the screen. Later tubes have a very thin layer of Aluminium deposited on the inside of the glass. This stops the electrostatic deflection caused by your hand/body which is (or should be) near ground/earth potential.

I am not sure of this now Steve as i tried this to no effect to the raster at all ..makes me wonder this tube is a later improved version ...

On some datasheets you may notice a word similar to 'Aluminiumised', that refers to this process that has been applied to the tube. A side effect is that in some tubes it reflects light from the rear of the phosphor forwards making the trace a bit brighter.

Steve A.

I also after your suggested procedure looked again at brightness before effecting focus ,,,,,,,..i now do not see this ......line seems fine with low light to higher ..no focus problem .

I adjusted the Bias before Tr401 was 225v Tr402 178 v......Tr501 208 v Tr502 200 v................After adjustment Tr401 230 v Tr402 180 v Tr501 194 Tr502 186 v...................On the Tr501 and 2 Bias control set to its limit for this adjustment ....

I found the focus control did seem to work better and i tried the astig and the effect i could see is merging the lines.
I tried dropping the size of the raster for a the line should be smaller and it is trying this even at this size i could see it doing a higher line rate.

youtu.be/bvwjKP88XE8

It's possible that the aluminium coating has been applied, often CRTs had a suffix to indicate a change in the basic design or manufacturing process. In this case it may mean the coating process has been implemented. i.e. the change from a VCR139 to a VCR139A. Other changes, usually to the focus anode to reduce focus current, often resulted in an A or B suffix.

Looking at the last photo above I would say that's about the limit for the focus and is about the best the tube could deliver. Compared to the earlier photos it's vastly improved.

Steve A.