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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Thu Oct 08, 2020 1:10 am 



Joined: 17 Aug 2020
Posts: 113
My Geiger counter arrived. It is the latest version of the GMC-300e Plus, which is available on Amazon for $75. It uses the M4011 Geiger-Muller tube or the J305 Geiger-Muller tube, which both use a thin glass casing, which makes it good for detecting both low energy and high energy x-rays. Revisions of the M4011 tube are known to be sensitive to harmless visible light radiation, but luckily the J305 tube does not have this issue. I opened the counter to check the tube model and luckily I won the tube lottery!
Image

Here is the reading that I get with the back plastic case of the GMC-300e Plus removed to fully expose the Geiger-Muller tube. Low energy x-rays have difficulty passing through solid materials, so removing the back plastic case helps increase the sensitivity of the device. Low energy x-rays also cannot travel very far in air. So I had it held up against the CRT screen in the center, then at the edges of the screen, the sides of the TV, and the back. It fluctuates around 0.08 to 0.1 micro-sieverts per hour when the TV is on at full white and the mod is enabled.
Image

Some context: if I walk around my house with this Geiger counter, I get the same range of readings is the same. In other words, the CRT is not emitting any x-ray radiation, even when the mod is active and the screen is full white (peak emissions). My granite counter top emits more radiation at around 0.13 micro-sieverts per hour. 0.03 micro-sieverts per hour up to 0.33uSv/h is considered normal, healthy background levels of radiation.

Modern CRTs, even with this mod, do not emit x-ray radiation. Significantly higher voltage (50 kilovolts) would be needed to cause a modern CRT to emit x-rays. The citations that I have linked explain why this is the case, and the measurements with a real Geiger-Muller tube that is sensitive enough to detect low energy x-rays confirms the theory is true. So fear not when moving forward with this mod. It is far below the voltage levels needed to cause your CRT to emit x-rays.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Fri Oct 09, 2020 7:17 pm 



Joined: 17 Aug 2020
Posts: 113
Out of curiosity, I measured everything in my house using this Geiger counter. None of my CRTs emit any X, beta, or gamma radiation. However, the ceramic tiles in my bathroom do emit radiation. The tiles were made in 1940, and must have used a uranium oxide glaze, which was common during that time.
Image

CRT gamers should worry more about keeping a safe distance from their bathroom tiles and granite counter tops than their CRTs. Though apparently CRT TVs from the 1940s thru 1950s do trigger these Geiger counters because the screen glass is thin.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sat Oct 10, 2020 10:53 am 


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Cheers for going the extra mile on this one. I appreciate the effort you've been putting in, and i'm sure others do too. I'd be interested to hear about subbing transistors and the other ideas you had too.

Hopefully soon i'll get around to trying out the mod for myself. Unless i can convince thumptech we need to get together and use one of his haul of old CRTs :)


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sat Oct 10, 2020 12:47 pm 



Joined: 02 May 2017
Posts: 6
buttersoft wrote:
... Unless i can convince thumptech we need to get together and use one of his haul of old CRTs :)


I've been meaning to give it a go, I have a couple of trinitron sets I think this may work well with, but I can't decide if i want to wrap more turns on the flyback or make a SMPS to provide the extra bias. I would also need my mister back as that is my test pattern generator ;)

I could try it on the bench with the variac, but I would say there is enough evidence in this thread already to go with a permanent mod rather than prove the concept again.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Mon Oct 12, 2020 4:00 pm 



Joined: 17 Aug 2020
Posts: 113
thumptech wrote:
buttersoft wrote:
... Unless i can convince thumptech we need to get together and use one of his haul of old CRTs :)


I've been meaning to give it a go, I have a couple of trinitron sets I think this may work well with, but I can't decide if i want to wrap more turns on the flyback or make a SMPS to provide the extra bias. I would also need my mister back as that is my test pattern generator ;)

I could try it on the bench with the variac, but I would say there is enough evidence in this thread already to go with a permanent mod rather than prove the concept again.


I expect the results generated by this mod to vary quite significantly from CRT to CRT. The electron gun design will determine what the spot size vs G1 voltage curve looks like, and the flyback design may limit the peak G2 voltage that can be adjusted (without more significant modification). So just getting very convincing results from a consumer Trinitron, even if that is done with a bench power supply, will be very useful for the community to see.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Wed Oct 21, 2020 12:32 am 



Joined: 17 Aug 2020
Posts: 113
I am going to prototype an alternative version of this mod that upgrades the RGB drive amps to ZTX658 amps that can tolerate a higher voltage. It is only $2.67 for all 3 amps. Then I will use a simple voltage divider to tap into approximately 400 volts off the screen voltage and use that as the voltage source for the RGB drive amps collector pin.

The advantage of this variation of the mod is it will be easier to implement since charging the G1 requires adding another winding to the flyback, which is labor intensive. Modifying the RGB drive amps directly is also a good opportunity to increase their bandwidth through an upgrade to a more modern amp. The disadvantage to this approach is it requires even more headroom in the screen voltage potentiometer because whatever increase in voltage of the cathodes relative to G1 needs to be matched with an even larger increase in screen voltage relative to G1. Charging the G1 anode directly avoids this.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Mon Oct 26, 2020 8:05 pm 


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I have found a monitor that applies -68V on the G1 pin from the factory. I will follow up with more information and the results of doing so on a similar monitor that does not.
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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Mon Oct 26, 2020 8:35 pm 



Joined: 17 Aug 2020
Posts: 113
mikejmoffitt wrote:
I have found a monitor that applies -68V on the G1 pin from the factory. I will follow up with more information and the results of doing so on a similar monitor that does not.


It will be very exciting to see others experiment with this mod, especially because results will vary considerably based on CRT model. The magnitude negative voltage you will need to apply will vary greatly from CRT to CRT. It will largely depend on the physical distance between the cathodes, G1 anode, and the G2 anode, especially the size of the aperture in the G1 anode. Consumer CRTs use a very large aperture in the G1 anode, which causes them to have a very thick cathode ray, and therefore they need a very large magnitude negative voltage than what you'd see in a professional CRT, which tend to use a very small G1 aperture.

The Diamondtron based Viewsonic P225f applies -180v to G1 in its factory design. It is also one of the highest TVL CRTs ever made, being able to both address and resolve 1920 TVL! It outputs a cathode ray that is incredibly thin!

Applying a negative charge to G1 shifts the burden of outputting a very high cathode voltage relative to G1, from the RGB drive output amplifiers to a separate power rail for charging G1. The Viewsonic P225f uses RGB drive output amps that operate at a much lower voltage gain, which allows them to have a very high bandwidth as a result, since the cathode to G1 voltage differential needed for cutoff is accomplished through separate negative charging of G1. This is why extremely high TVL CRTs charge G1 to a very negative charge.

This page is a great overview of the physics of electromagnetic equipotentials that explains why increasing K-G1 and G2-G1 voltages decreases spot size. Basically, the cathodes and anodes are not point voltages in a circuit. They are three dimensional structures that give off electromagnetic fields. The "Grid" aka "G1" is a metal tube that surrounds the cathodes and has a tiny aperture at the end of it. The fields create a sort of path of greatest attraction that the cathode ray is pulled through by the G2 anode. The size of the surface area of the cathode where the voltage equipotential between G2 and cathodes is absolute zero shrinks as K-G1 and G2-G1 voltages increase.
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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Fri Nov 13, 2020 9:59 pm 


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Posts: 119
Location: Australia
This is one me of the coolest CRT modding ideas - simple to implement and effective at achieving its goals. Will there be any updates or progress reports anytime soon?


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sat Nov 14, 2020 11:22 am 



Joined: 07 Aug 2018
Posts: 63
I'm still planning to do that mod on a Sony consumer CRT. They are in the basement though and I don't have enough space upstairs at the moment. I need to get rid of.some CRTs first.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sat Dec 26, 2020 4:49 am 


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It took me a long time to get around to writing this up: http://mikejmoffitt.com/pages/ms9-hax
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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sat Dec 26, 2020 1:16 pm 



Joined: 07 Aug 2018
Posts: 63
That's a very interesting read. Thanks!

I wonder why they set G1 to GND in the later model. The savings are minimal as they basically only save a diode, resistor and a capacitor. The flyback is still providing the negative voltage even though it is not used. That seems weird to me.

Also interesting about the VGA conversion. Changing the inductance of the horizontal size coil may help to widen the picture. That will of course also change it at 15kHz.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Wed Dec 30, 2020 3:58 pm 


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mikejmoffitt wrote:
It took me a long time to get around to writing this up: http://mikejmoffitt.com/pages/ms9-hax


Mike, fantastic writeup. Question about the S correction going from 15 to 31 KHz. The way you handle it is similar to the cap mod done to the Wei-ya M3129 correct?

Also, do you have any before/after pics from the G1 voltage mod?


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Tue Jan 05, 2021 10:00 pm 



Joined: 07 Aug 2018
Posts: 63
I did the G1 mod on a Sony KV-A3411D that has a normal G1 voltage of +30V. I changed it to -80V.

You can see the difference here:

https://i.imgur.com/o3y8Z2M.jpg

https://i.imgur.com/GX0zLsy.jpg

Once again, I can not go more negative with the voltage because I am running out of G2 voltage.

This was just a quick test. I'm gonna try to wrap some turns around the flyback and get my -80V from there and write a thorough report.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Tue Jan 05, 2021 11:56 pm 


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The lower picture definitely looks more granular /defined. Your vertical convergence is really a sight to behold, man it looks great.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Wed Jan 06, 2021 8:51 am 



Joined: 18 May 2011
Posts: 8
Can we hope one day, a tuto for beginners to make this mod on crt tv ?
I have several trinitron screens with an fe-2 chassis and I would love to be able to test this. Thank you very much.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Wed Jan 06, 2021 9:31 am 



Joined: 07 Aug 2018
Posts: 63
Josh128 wrote:
The lower picture definitely looks more granular /defined. Your vertical convergence is really a sight to behold, man it looks great.


Haha, on the bottom left corner the red vertical convergence is pretty bad.

Also as seen before this mod really highlights bad convergence due to the smaller spot size.

Zoom in here: https://i.imgur.com/NS5vQMc.jpg

You can see that red is slightly higher than the rest of the beams. I need to properly adjust the convergence after I'm done experimenting.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Wed Jan 06, 2021 9:46 am 



Joined: 07 Aug 2018
Posts: 63
yoZe wrote:
Can we hope one day, a tuto for beginners to make this mod on crt tv ?
I have several trinitron screens with an fe-2 chassis and I would love to be able to test this. Thank you very much.


I'm gonna try to build a power supply using the flyback of the TV. If that is successful I'm going to do a writeup on how to do it.
Unfortunately every TV is different so not everything can be transferred to other models.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Wed Jan 06, 2021 10:23 pm 


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ElBartoME wrote:
Josh128 wrote:
The lower picture definitely looks more granular /defined. Your vertical convergence is really a sight to behold, man it looks great.


Haha, on the bottom left corner the red vertical convergence is pretty bad.

Also as seen before this mod really highlights bad convergence due to the smaller spot size.

Zoom in here: https://i.imgur.com/NS5vQMc.jpg

You can see that red is slightly higher than the rest of the beams. I need to properly adjust the convergence after I'm done experimenting.


Ah yes, after reexamining the pics I see what you mean. Im struggling with similar vert convergence issues on my 36". That may just be as good as it gets though. It sucks that once you notice these little shits, its all you can think about, it drives me nuts!


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Thu Jan 07, 2021 8:04 pm 


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If you all think those are examples of bad convergence never look at my FV310, it's god awful.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Thu Jan 07, 2021 10:38 pm 



Joined: 07 Aug 2018
Posts: 63
So I did some testing with getting the required voltage for G1 from the flyback.

I was able to get -100V for G1 by wrapping some turns around the core of the flyback and using a diode, capacitor and resistor. It works but I still have a bit of a problem with ghosting but I think this is due to the lack of filtering on the neckboard itself. I ran out of time but I'm gonna add a filter and check the picture.

Image

Image

Image


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Fri Jan 08, 2021 2:50 am 


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FWIW, I had some weird streaking issues when I had a long and/or thin G1 wire, but I have no proof that it was not actually unrelated. However, when I wired it up "properly" later, with some neater work, those issues went away.

If I end up with a Blast City again, I'd like to probe the flyback to see if it has a winding already present on a pin for an appropriate G1 voltage. Otherwise, I'll likely do the same, winding my own supply off the flyback core. The MS-2930 with a good tube tends to already be quite sharp, so I am curious how it would look after trying a negative G1 voltage.
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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Fri Jan 08, 2021 1:16 pm 



Joined: 07 Aug 2018
Posts: 63
mikejmoffitt wrote:
FWIW, I had some weird streaking issues when I had a long and/or thin G1 wire, but I have no proof that it was not actually unrelated. However, when I wired it up "properly" later, with some neater work, those issues went away.


I also suspect this might be the problem as the long cable introduces some inductance. It also got worse for me when I was playing around with the cabling. That's why I'm going to add filtering directly on the neckboard. The original schematic uses a filter consisting of a resistor and capacitor but I had to remove it as it uses an electrolytic capacitor. Considering it used a G1 voltage of +20V before that capacitor will pop if I put a negative voltage across it.

I'm gonna replace that capacitor with another electrolytic cap that can also withstand higher voltage and of course reverse the polarity when putting it back in the circuit.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sat Jan 09, 2021 4:08 pm 



Joined: 07 Aug 2018
Posts: 63
So I finalized my mod and I'm going to do a write-up soon.

I just wanted to say that putting in the filter and tidying up the cables did fix the streaking issue. I'm relieved and the picture looks amazing!


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sat Jan 09, 2021 4:37 pm 


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ElBartoME wrote:
So I finalized my mod and I'm going to do a write-up soon.

I just wanted to say that putting in the filter and tidying up the cables did fix the streaking issue. I'm relieved and the picture looks amazing!



Care to post any screen shots of the final mod?


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sat Jan 09, 2021 5:58 pm 



Joined: 07 Aug 2018
Posts: 63
So finally here my write-up.

After I did some testing on a PVM-14N2 and a PVM-1442QM I decided to try the G1 mod on a Sony consumer. I picked up a Sony KV-A3411D (34 inch) some months ago as I was very interested in a big Sony consumer as my main screen.

Well after picking it up I was pretty disappointed with the picture as it would get insanely blurry when the contrast was cranked up above a third. I suspected the tube had very high hours on it. I tried some stuff like gently rejuvenating the cathodes but with no success. I finally decided to do the G1 mod on it and here are my results.


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

Image

I had a look at the service manual and this is what I found:

Image

Most trinitrons have three different G1 pins mostly labeled G1-1, G1-2, G1-3 or something like G1R, G1G, G1B. In my unit only G1-1 is used and the other two pins are not connected to anything. This is because inside the tube the three different G1 grids for the colours are connected together. I'm not entirely sure why they bring out all three pins though.

Having a look at the schematic you can see that G1 is connected with a voltage divider (consisting of R740 and R741) to 200V. That leaves us with a G1 voltage of +30V. The only idea I have why they used a positive G1 is to not have a small spot size in order to reduce flickering with 480i content (what probably 95% of people did back in the day with these TVs).

There is also a filter consisting of R738 and C721. For my tests I had to remove it because the capacitor is an electrolytic one and if I put a negative voltage across it, it will go pop. Also it is only a 50V kind so it will not be able to withstand the voltage anyway.

What I did is remove R740, R741 and R738. I connected a variable power supply with the POSITIVE lead to ground (called E in the schematic) and the NEGATIVE lead to G1-1.

I turned the power supply on and set it to 0V. Then I turned on the TV and fired up 240p test suite. I then cranked up the voltage. You will notice while G1 goes more negative the screen will become dimmer. That makes sense as the negatively charged G1 will repel the electrons from the gun and therefore the picture will be darker. To compensate this you need to crank up G2 (also called SCREEN). There is a potentiometer either on the neckboard (like on my TV) or on the flyback itself. This is what I did. Going more negative with G1 and in turn going more positive with G2. I reached a voltage of -100V for G1 until I was at the end of the potentiometer for G2. So that was the end of the line. I was a bit disappointed as I had hoped to go higher but I had a look at the picture and wow, it was much more defined.

Here are two comparisons. Left is with +30V G1 (original) and right is with -100V. One thing to keep in mind though for the comparison is, that the picture on the left has been done with the contrast at around a third. Otherwise it was very blurry. On the right side the contrast was set to about two thirds. The picture on the right side was much brighter and still much more defined.

Image
Click here for high resolution: https://i.imgur.com/LTCwG3e.jpg

Image
Click here for high resolution: https://i.imgur.com/W2oilYX.jpg

Alright, cool. But I don't want to have a high voltage power supply connected to the TV the whole time. I read the idea about wrapping some turns around the flyback core to get the desired voltage. So I gave it a try.

I built myself a small PCB with the following schematic:

Image

The PCB itself just consists of a diode (I chose a fast 400V diode, don't use slow diodes like a 1N400X), two resistors and a capacitor. The capacitor is a film capacitor I had laying around. I suggest using a film capacitor but an electrolytic capacitor will probably work too. 400V is just what I had and is overkill. 200V would have been more than enough. The 1 Ohm resistor in series to C1 is to limit the initial charging current to reasonable levels.

Here the PCB:

Image

I put in connectors so I can easily remove the PCB to work on it. I didn't connect the PCB to the neckboard yet. I wrapped some turns around the flyback and checked the voltage at the output of R2. With 5 turns I had around 30V so I wrapped 15 turns around the flyback. That bumped it up to almost exaclty 100V.
But beware: The polarity of the coil is important as we only do a single wave rectification and flyback pulses are not AC, they are positive pulses. I first connected the coil backwards and my output voltage was very low. I then switched the polarity and my voltage was higher. So if you don't get enough voltage first try to flip the polarity of the coil!

Image

I then connected the PCB to the neckboard according to the schematic. At that time the filter consisting of R738 and C721 was still disconnected. The picture looked fine, but I had some kind of streaking on the picture. I then went back and tidied up my cabling and modified the filter and put it back in the circuit. I reused R738 but I replaced C721 with a 10µF 200V electrolytic capacitor. The polarity of that capacitor needs to be flipped as we now have negative G1 voltages instead of positive!!!

I then secured the board with zip-ties and closed up the case again.

Image

I'm very happy with the result. :D :D :D

Image



Note: Normally when doing this mod you need to also adjust the cut-offs for each colour channel. I got lucky as the KV-A3411D automatically adjusts the cut-off. There is not even a potentiometer to change the cut-off, only the gains (no service menu on that model btw).


Last edited by ElBartoME on Sun Jan 10, 2021 11:39 am, edited 1 time in total.

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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sat Jan 09, 2021 7:22 pm 


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Cool stuff. Best part about all this is the fun you have in doing it!


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sat Jan 09, 2021 8:12 pm 



Joined: 05 Jan 2021
Posts: 16
Location: Germany
Josh128 wrote:
Cool stuff. Best part about all this is the fun you have in doing it!



I know him .. a total master.

I call him Doctor Frankenstein the cathode master. :lol:


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sun Jan 10, 2021 12:46 am 



Joined: 17 Aug 2020
Posts: 113
mikejmoffitt wrote:
It took me a long time to get around to writing this up: http://mikejmoffitt.com/pages/ms9-hax


Interesting that the MS9 regressed the spot size relative to the MS8. Your hack corrects for this. Nice work!

ElBartoME wrote:
So finally here my write-up.
...


Your side-by-sides really nail it and are way better results than what I was able to get with my consumer Panasonic CRT TV, and the fact that you built your own power supply using windings on the exposed core really cements the mod as a nice permanent improvement. I am going to include, with credit, your side-by-sides in OP, as I think they are more convincing that this mod is worth it.

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!


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



Joined: 17 Mar 2018
Posts: 160
Location: Germany
Amazing results! Thanks for the write-up.


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