Colour CRTs suitable for NBTV - UK Vintage Radio Repair and Restoration Discussion Forum

dominicbeesley · 24th Sep 2008, 7:29 pm

Hello all,

Please can I pick the brains of all the telly experts...

I've managed to get sidetracked whilst building my latest NBTV creation into the realms of colour. I've "invented", well thrown together, some software to produce a colour compatible 32line NBTV/NTSC standard and a recorder and playback software. [read about it here] I still can't believe it works!

The whole thing fits into a 20kHz bandwidth too!

I'd now like to actually make a receiver of some kind. Eventually I'd like to build a mechnical viewer but in the meantime I'd also like to try and botch together something using a small colour CRT. Trouble is I've no idea where to start, I'm hoping with the combined wisdom of the group I might be able to get something up and running quickly...

If I get a small relatively modern colour portable or small computer monitor and use the CRT:

Will I still need thousands of volts on the anode or is there any way to "underrun" them: this works ok on monochrome tubes but I'm guessing that modern aperture grille CRTs won't converge?

If I can underrun the anode will this reduce the amount of juice I'll need to run the scan coils?

If I still need the full EHT would it be possible in a relatively straightforward set to still run the LOPT circuitry without the scan coils connected? I could then leave the set running as normal for the EHT/Focus but hijack the scan coils/grids/cathodes of the CRT?

Any hints, suggestions, references to a decent psychiatrist would be very welcome.

Dom

Danny · 27th Sep 2008, 9:39 pm

Hi i would track down a little battery portable with a 5" screen the ones with narrow scanning . thay were also available with radio cassette recorder built in you will then need some dummy coils to replace the line coils so the line timebase is still operative then you can do what you whant with the coils that are on the tube . next locate the video driver transistors and again you can easily highjack the video at the bases. it is possible to build the hole thing from scratch with valves. but you will still need the high eht and focus voltages . Danny

Maarten · 28th Sep 2008, 7:01 pm

Under running will probably affect focussing more then it will affect convergence. I wouldn't reccomend it.

dominicbeesley · 28th Sep 2008, 10:08 pm

I'd probable want some level of de-focusing, either by deliberately defocusing or by some kind of "dot-wobble".

Either way, I've been having a good look round on e-bay and the only mini-CRT thing I've found was quite expensive...

Dom

DrZarkov · 1st Oct 2008, 8:37 pm

I would not use a CRT at all, but a mirror-drum or a Nipkow-disc and LEDs. No high voltage, and no problem with 32 lines on a colour CRT made for much more lines. If you prefer a CRT why not a black and white CRT and a rotating colour-wheel?

dominicbeesley · 1st Oct 2008, 11:14 pm

Quote:

Originally Posted by DrZarkov

I would not use a CRT at all, but a mirror-drum or a Nipkow-disc and LEDs.

I'm working on it, I'd just like to try it out on a CRT too...

Quote:

Originally Posted by DrZarkov

No high voltage, and no problem with 32 lines on a colour CRT made for much more lines.

High voltage, but my hair doesn't stick out at the right angle unless I get a shock every now and again!

Quote:

Originally Posted by DrZarkov

If you prefer a CRT why not a black and white CRT and a rotating colour-wheel?

That's for later, I'm going to look into it but I reckon at 12 1/2 frames per second divided by 3 then even I'll get a headache!

Cheers

Dom

Trish · 2nd Oct 2008, 12:25 am

I think DrZarkov is on the right track.

You can get high power (over three watt) RGB LED's.. And I can tell you that they are really bright. I have used them to expose optical soundtracks on film. I found that I could set up a colour, and it would be pretty stable. I haven't tested them for linearity/tracking regarding modulating them. But IMO it is worth a go..

Trish

dominicbeesley · 2nd Oct 2008, 9:06 am

Yes, I agree: I've just received a nice Nipkow disc and I've just ordered a load of LEDs and I'll be trying various different types out. The ones I've just ordered are superflux ones, nice and small but aparently quite bright, if those aren't bright enough I'll try bigger 3W ones but would prefer many small rather than few large so I can get a nice overlap of red green and blue.

However that's likely to get is into trouble for being off topic - I still want to build a CRT NBTV receiver, not for any good reason other than (to see if) I can. I've a few other ideas where I'd like to try underrunning (in both terms of line/frame frequency and EHT) or otherwise "misusing" colour CRTs.

Thanks

Dom

Trish · 15th Nov 2008, 3:25 pm

Apologies for raising this thread from the depths.. I found some interesting items during a search for something completely different about my local Radio club..

It might be worth some more research.. I have to admit that I hadn't heard about the Narrow-bandwidth Television Association until now..

---> 30 Line Television

---> Amateurs Turn Back the Clock on Television Technology

Trish

24th Sep 2008, 7:29 pm	#1
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	Colour CRTs suitable for NBTV Hello all, Please can I pick the brains of all the telly experts... I've managed to get sidetracked whilst building my latest NBTV creation into the realms of colour. I've "invented", well thrown together, some software to produce a colour compatible 32line NBTV/NTSC standard and a recorder and playback software. [read about it here] I still can't believe it works! The whole thing fits into a 20kHz bandwidth too! I'd now like to actually make a receiver of some kind. Eventually I'd like to build a mechnical viewer but in the meantime I'd also like to try and botch together something using a small colour CRT. Trouble is I've no idea where to start, I'm hoping with the combined wisdom of the group I might be able to get something up and running quickly... If I get a small relatively modern colour portable or small computer monitor and use the CRT: Will I still need thousands of volts on the anode or is there any way to "underrun" them: this works ok on monochrome tubes but I'm guessing that modern aperture grille CRTs won't converge? If I can underrun the anode will this reduce the amount of juice I'll need to run the scan coils? If I still need the full EHT would it be possible in a relatively straightforward set to still run the LOPT circuitry without the scan coils connected? I could then leave the set running as normal for the EHT/Focus but hijack the scan coils/grids/cathodes of the CRT? Any hints, suggestions, references to a decent psychiatrist would be very welcome. Dom Attached Thumbnails

27th Sep 2008, 9:39 pm	#2
Danny Heptode Join Date: Jul 2003 Location: North Walsham, Norfolk, UK. Posts: 516	Re: Colour CRTs suitable for NBTV Hi i would track down a little battery portable with a 5" screen the ones with narrow scanning . thay were also available with radio cassette recorder built in you will then need some dummy coils to replace the line coils so the line timebase is still operative then you can do what you whant with the coils that are on the tube . next locate the video driver transistors and again you can easily highjack the video at the bases. it is possible to build the hole thing from scratch with valves. but you will still need the high eht and focus voltages . Danny

28th Sep 2008, 7:01 pm	#3
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 4,199	Re: Colour CRTs suitable for NBTV Under running will probably affect focussing more then it will affect convergence. I wouldn't reccomend it.

28th Sep 2008, 10:08 pm	#4
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	Re: Colour CRTs suitable for NBTV I'd probable want some level of de-focusing, either by deliberately defocusing or by some kind of "dot-wobble". Either way, I've been having a good look round on e-bay and the only mini-CRT thing I've found was quite expensive... Dom

1st Oct 2008, 8:37 pm	#5
DrZarkov Retired Dormant Member Join Date: Jun 2007 Location: Herongen, Germany Posts: 65	Re: Colour CRTs suitable for NBTV I would not use a CRT at all, but a mirror-drum or a Nipkow-disc and LEDs. No high voltage, and no problem with 32 lines on a colour CRT made for much more lines. If you prefer a CRT why not a black and white CRT and a rotating colour-wheel?

2nd Oct 2008, 12:25 am	#7
Trish Retired Dormant Member Join Date: Apr 2005 Location: Reading, Berkshire, UK. Posts: 95	Re: Colour CRTs suitable for NBTV I think DrZarkov is on the right track. You can get high power (over three watt) RGB LED's.. And I can tell you that they are really bright. I have used them to expose optical soundtracks on film. I found that I could set up a colour, and it would be pretty stable. I haven't tested them for linearity/tracking regarding modulating them. But IMO it is worth a go.. Trish

2nd Oct 2008, 9:06 am	#8
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	Re: Colour CRTs suitable for NBTV Yes, I agree: I've just received a nice Nipkow disc and I've just ordered a load of LEDs and I'll be trying various different types out. The ones I've just ordered are superflux ones, nice and small but aparently quite bright, if those aren't bright enough I'll try bigger 3W ones but would prefer many small rather than few large so I can get a nice overlap of red green and blue. However that's likely to get is into trouble for being off topic - I still want to build a CRT NBTV receiver, not for any good reason other than (to see if) I can. I've a few other ideas where I'd like to try underrunning (in both terms of line/frame frequency and EHT) or otherwise "misusing" colour CRTs. Thanks Dom

15th Nov 2008, 3:25 pm	#9
Trish Retired Dormant Member Join Date: Apr 2005 Location: Reading, Berkshire, UK. Posts: 95	Re: Colour CRTs suitable for NBTV Apologies for raising this thread from the depths.. I found some interesting items during a search for something completely different about my local Radio club.. It might be worth some more research.. I have to admit that I hadn't heard about the Narrow-bandwidth Television Association until now.. ---> 30 Line Television ---> Amateurs Turn Back the Clock on Television Technology Trish