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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sun Jan 10, 2021 11:41 am 



Joined: 07 Aug 2018
Posts: 42
LukeEvansSimon wrote:

Before I got distracted by family, work, other hobbies, and the US presidential election, I was working on designing and testing a from scratch new CRT neck board that uses a cathode amplifier design that has around 30 mhz chroma signal bandwidth for amplification of the RGB chroma signals up to 200 volts peak to peak. The design uses a "cascode" amplifier design, as well as Sanyo's discrete NPN transistor 2SC3782 that were used in 1080i HDTV CRTs. For generating the negative voltage rail for the G1, my "super neck board" design uses an inexpensive pulse transformer. This allows for tapping the unrectified cathode amplifier rail coming off of the flyback, to create a separate negative voltage rail that is 2x the voltage of the cathode amplifier rail (which is usually around 200 volts).

The idea is for the "super neck board" to take 5 minutes to install for somebody with beginner soldering skills, and by significantly increasing cathode amplifier bandwidth, further resolution improvements will be realized, in addition to those realized by increasing K to G1 and G2 to G1 voltage differentials. I've done all of the LTSpice simulations, ordered all of the parts, and I just need to breadboard prototype it now. I found a HUGE new old stock supply of 2SC3782 NPN transistors. Higher bandwidth transistors have been made since the 2SC3782, but they are not capable of the 200 volts peak to peak amplification that the 2SC3782 is capable of. The 2SC3782 is insane!


Your custom neckboard sounds very interesting! Don't you need to adapt it to different sockets as not every tube uses the same pinout? How are you going to do that? I'm eager to see the results.

Also I'm debating on removing R709 so my G2 can go a bit higher. Not sure if this will cause any problems...

Theoretically I could use a voltage doubler and tap into the G2 voltage before it gets rectified but my concern is will this cause problems with the potentiometer for the screen voltage? It is not designed for that voltage and may arc. Also I'm not sure what the clearance is between G2 and G1. If I double G2 can this cause arcing between the two grids?

I have a Sony TV with a very worn tube. I might try doubling G2 on that TV before I accidentally kill my precious 34 inch Sony. :D


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sun Jan 10, 2021 2:33 pm 



Joined: 16 Dec 2008
Posts: 4
ElBartoME wrote:
Here you can see the A3411D on the right side. On the left side is a KV-29X5D (29 inch) as a size comparison.


Nice work! Are you going to do this on the 29 inch too? I have the same model (KV-29X5D) with a blurry screen and would be very interested in the how-to/results.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sun Jan 10, 2021 7:03 pm 



Joined: 17 Aug 2020
Posts: 86
ElBartoME wrote:
Your custom neckboard sounds very interesting! Don't you need to adapt it to different sockets as not every tube uses the same pinout? How are you going to do that? I'm eager to see the results.


I need to find the time to get back to my CRT projects, but so many other things in life are taking up my time. The super neckboard PCB will come in two versions: one that uses the B10-277 socket, which will support most shadow mask tubes, and another that will use a socket to cover most aperture grille tubes. Because I mostly collect slot mask tubes, I am starting with the B10-277 version.

The super neckboard will also include a 70mhz bandwidth jungle chip: Texas Instrument's LM1203. So there will be two ways to wire up the super neckboard. You can wire it up to use the jungle chip already in your chassis, but if your chassis's jungle chip is not high bandwidth, then max resolution will be bottlenecked by it. The other way to wire it up will be to just have the input RGB signal feed straight to the LM1203 on the super neckboard. I found new old stock of LM1203s, so it will be low cost to include this feature. The disadvantage of using the LM1203 is that there is no on screen display, so pots on the neckboard have to be used to tune RGB bias (aka brightness) and gain (aka contrast). However, tuning these pots is only required once, during installation of the neckboard.

The biggest challenge for a CRT neckboard are the cathode amplifiers. Amplifying a 5 volt peak to peak signal up to a 200 volt peak to peak signal at 30 mhz bandwidth is impressive. Professional CRTs use smaller electron guns that run at a lower voltage than consumer CRTs that use electron guns that run at higher voltage. A PC CRT or BVM have cathodes that are run at around 50 volts peak to peak, whereas your consumer CRT TV has cathodes that are run at 200 volts peak to peak. The cathode amplifiers used in the large consumer HDTV CRTs are by far, more capable than the amplifiers used in BVMs. However, every CRT gamer knows that HDTV CRTs have horrible laggy circuits that are terrible for gaming. So my super neckboard is backporting the HDTV cathode amplifiers to 15khz SDTVs so we can have the best of both worlds: zero lag and yet ultra high bandwidth video amplication at consumer CRT high voltage.

ElBartoME wrote:
Also I'm debating on removing R709 so my G2 can go a bit higher. Not sure if this will cause any problems...

Theoretically I could use a voltage doubler and tap into the G2 voltage before it gets rectified but my concern is will this cause problems with the potentiometer for the screen voltage? It is not designed for that voltage and may arc. Also I'm not sure what the clearance is between G2 and G1. If I double G2 can this cause arcing between the two grids?

I have a Sony TV with a very worn tube. I might try doubling G2 on that TV before I accidentally kill my precious 34 inch Sony. :D


It is important to preserve large curved consumer CRTs. The small PC CRTs and RGB monitors came into popularity very late in the era of CRTs, and yet many CRT gamers are trashing large curved consumer CRTs at a very high rate compared to the small PC CRTs and RGB monitors. As I mentioned above, the electron gun design and video amplifier design in pro CRTs are different than consumer CRTs. One is not superior to the other, just as a PS5 is not superior to a PS1.

The pot that is in series with R709 needs both a current rating and voltage rating to handle the increased current and voltage that it will need to endure if R709 is removed. So you can upgrade the pot too, in order to be safe.

Another model consumer CRT that would likely benefit greatly from this mod is the Mitsubishi CS-40809. It is a 40-inch bubble curved slot mask consumer CRT TV with component! However, the neckboard is designed to have the G1 voltage near zero and so the blank scanlines in 240p content are very thin. You can see a CRT gamer demonstrate the scanlines in this YouTube video. Compared to the smaller 36-inch JVC D-Series, which is also a bubble curved slot mask tube, the Mitsubishi CS-40809's blank scanlines are no where near what they could achieve with a more negative G1 voltage.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Mon Jan 11, 2021 9:45 am 


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Joined: 24 Jul 2016
Posts: 309
Ok, that neckboard sounds totally hawt. If you can keep the price down, and shipping is reasonable, I'm sure thumptech and i will put in an order for a few each.

EDIT: any chance the little transformer is going to be easily adjustable? It would be nice to be able to tweak the effect for different sizes/CRTs/games/viewing distances :)


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Mon Jan 11, 2021 11:28 am 



Joined: 07 Aug 2018
Posts: 42
Does the LM1203 include automatic cut-off control? I noticed that the automatic cut-off control of my TV made the process so much easier. My TV uses the TDA4580 (https://datasheetspdf.com/pdf-file/378437/NXP/TDA4580/1) that implements the automatic cut-off. Unfortunately it seems to only have a bandwith of 10 MHz.


Also I decided to move R709 after the pot. That should increase G2 at the tube but the current through the pot should still remain the same. I'm gonna try that the next time I have the TV open.

zebius wrote:
ElBartoME wrote:
Here you can see the A3411D on the right side. On the left side is a KV-29X5D (29 inch) as a size comparison.


Nice work! Are you going to do this on the 29 inch too? I have the same model (KV-29X5D) with a blurry screen and would be very interested in the how-to/results.


Yes, my 29X5D suffers also from a bit of blur. If I find the time I will mod it too.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Tue Jan 12, 2021 12:23 am 



Joined: 17 Aug 2020
Posts: 86
buttersoft wrote:
Ok, that neckboard sounds totally hawt. If you can keep the price down, and shipping is reasonable, I'm sure thumptech and i will put in an order for a few each.

EDIT: any chance the little transformer is going to be easily adjustable? It would be nice to be able to tweak the effect for different sizes/CRTs/games/viewing distances :)


The super neckboard will have a pot for tuning G1 voltage, which means you can tune for the cathode ray spot size that matches your tastes. The smaller the spot size, the thicker the blank scanlines, and the illuminated scanlines will be sharper. As mentioned in this thread, tuning G1 voltage requires a second step: tuning the G2 voltage. This is the price to pay for adjustable thickness real scanlines.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Tue Jan 12, 2021 10:18 am 



Joined: 17 Mar 2018
Posts: 137
Location: Germany
LukeEvansSimon wrote:
[...] So my super neckboard is backporting the HDTV cathode amplifiers to 15khz SDTVs so we can have the best of both worlds: zero lag and yet ultra high bandwidth video amplication at consumer CRT high voltage. [...]


This is a super interesting topic that deserves its own thread entirely, imo.

I was hoping of one day finding a way of displaying 480p on the plethora of 100Hz TVs that are available in Europe, but I lack the knowledge on how to do so. Would you be willing to give a couple of pointers about what can still be used and what can't? I was always under the impression that 100Hz TVs essentially run on a 31kHz signal ("240p120") and indeed, some manufacturers like Grundig and Metz offer a VGA Port that supports 480p60, but my understanding does not go deep enough. Do you think it's possible to tap into a standard 100Hz TV and display a VGA signal with some kind of custom board?

And on the other hand: how are you planning on displaying 15kHz signals on an HD CRT, what is the limiting factor usually that VGA displays and HD CRTs cannot sync as low as 15kHz? (Kind of a noob question :mrgreen: )


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Wed Jan 13, 2021 4:37 am 



Joined: 17 Aug 2020
Posts: 86
SuperSpongo wrote:
LukeEvansSimon wrote:
[...] So my super neckboard is backporting the HDTV cathode amplifiers to 15khz SDTVs so we can have the best of both worlds: zero lag and yet ultra high bandwidth video amplication at consumer CRT high voltage. [...]


This is a super interesting topic that deserves its own thread entirely, imo.

I was hoping of one day finding a way of displaying 480p on the plethora of 100Hz TVs that are available in Europe, but I lack the knowledge on how to do so. Would you be willing to give a couple of pointers about what can still be used and what can't? I was always under the impression that 100Hz TVs essentially run on a 31kHz signal ("240p120") and indeed, some manufacturers like Grundig and Metz offer a VGA Port that supports 480p60, but my understanding does not go deep enough. Do you think it's possible to tap into a standard 100Hz TV and display a VGA signal with some kind of custom board?

And on the other hand: how are you planning on displaying 15kHz signals on an HD CRT, what is the limiting factor usually that VGA displays and HD CRTs cannot sync as low as 15kHz? (Kind of a noob question :mrgreen: )


CRT displays have 4 main parts to their circuits: (i) power supply for converting AC to DC, (ii) deflection for scanning the 3 cathode rays across the screen, (iii) chroma signal amplification for changing the intensity of the 3 cathode rays as they are scanned across the screen, and (iv) CRT anode charging for shaping the cathode ray and accelerating it towards the screen. The super neckboard modifies (iii) and (iv). So the HDTV chroma amplifiers are being backported to SDTVs for very high bandwidth amplification. Deflection is not being modified at all. So if your CRT only does 15khz, then super neckboard won’t change that.

Cathode amplifier bandwidth is one of the 3 bottlenecks for TVL. The other 2 are cathode ray spot size and phosphor pitch. I can’t modify phosphor pitch for a reasonable cost, and so super neckboard is focusing on the other 2, which bottle neck TVL on most consumer CRTs.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Wed Jan 13, 2021 8:36 am 



Joined: 17 Mar 2018
Posts: 137
Location: Germany
Thanks for the additional insights :)


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Thu Jan 14, 2021 10:50 pm 



Joined: 02 May 2017
Posts: 6
SuperSpongo wrote:
Do you think it's possible to tap into a standard 100Hz TV and display a VGA signal with some kind of custom board?


I have achieved this on a 100hz Sony set. The Jungle IC accepted 480p RGBHV VGA signal from a scaler chip named the "Digital Reality Creation". I cut these traces and attached my own VGA port. It works very well with my Sega Dreamcast. I was also able to jack into the RGB lines for the teletext board - these were internally upscaled from 15khz to 31khz in the jungle IC and could be used with older consoles.

I am fairly sure this approach will work with most "100hz" sets.

I'll leave it at that as it is off topic.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Fri Jan 15, 2021 10:06 am 



Joined: 18 May 2011
Posts: 8
thumptech wrote:
SuperSpongo wrote:
Do you think it's possible to tap into a standard 100Hz TV and display a VGA signal with some kind of custom board?


I have achieved this on a 100hz Sony set. The Jungle IC accepted 480p RGBHV VGA signal from a scaler chip named the "Digital Reality Creation". I cut these traces and attached my own VGA port. It works very well with my Sega Dreamcast. I was also able to jack into the RGB lines for the teletext board - these were internally upscaled from 15khz to 31khz in the jungle IC and could be used with older consoles.

I am fairly sure this approach will work with most "100hz" sets.

I'll leave it at that as it is off topic.


If you could detail this by doing your own tutorial on another subject it would be a real revolution!
Indeed in europe we may have rgb on the SCART but our TV had no component input so it was impossible for us to benefit from 480p.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Tue Jan 19, 2021 2:19 pm 



Joined: 17 Mar 2018
Posts: 137
Location: Germany
If the interest is there we could open up another thread.


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