Mod a CRT to increase its TVL

[LukeEvansSimon]

I found a way to add a potentiometer for adjusting the G1 anode voltage without having to add a new winding to the flyback. This greatly simplifies the mod and allows it to be an unpluggable board that is added alongside the flyback (which already has pots for G2 and G3 voltage). CRTs have a flyback pin that is used to create a voltage rail for the vertical deflection circuit. In my TV, it is flyback transformer pin 8, and it generates a 250 volts peak to peak waveform



The idea is to move D561 and C562 to a new circuit board with the following schematic:

Moving D561 and C562 (C9 in the new board schematic) makes room on the main circuit board to add quick disconnect terminals that allow for unpluggable wires between the main board and the new circuit board. The new circuit board's design is straightforward. Diode D561 and capacitor C9 are to ensure that the vertical deflection circuit's voltage rail is preserved. R4 limits the current flow during powering on. Capacitor C1 and diode D2 accomplish what the additional winding accomplishes in ElBartoMe’s design. C1 is a simple coupling capacitor that provides galvanic isolation, yet provides a "new" 250vpp power source. Diode D2 ensures the new power supply is a negative voltage. Diode D3 is a rectifier to ensure the new power supply is DC. Cap C8 is a switching noise dampener. C5, R1, L1, and C3 act as a CRLC filter so that the power supply's DC voltage has minimal ripple and minimal noise. D5 provides more ripple reduction, and potentiometer U1 allows the user to control the voltage of the G1 "grid" anode.


In simulation the ripple voltage is a single microvolt peak to peak, but in real life, the ripple is 6 millivolts, which is not bad.



My CRT had a jumper that connects the G1 anode to ground. I desoldered that jumper and installed two quick disconnect terminals so that I could plug cables in that run from the new circuit board's ground and vcc terminals respectively.


Left picture is the potentiometer set to 0 volts, and right picture is the potentiometer set to -229 volts. If the potentiometer dial is tuned to a setting in the middle, then the picture looks halfway between the scanline thickness of the left and of the right.

Next weekend, I will solder a permanent perfboard version and install it inside the TV chassis next to the flyback so that G1, G2, and G3 potentiometers are all easily accessible.

[SuperSpongo]

That's so cool! So with this pot you can very easily demonstrate the effect of the G1 voltage on spot size. I bet it's so fun to play around with that pot

[ElBartoME]

Uhh, that is some nice work! Very interesting stuff. I'm right in the process of moving and I'm gonna have all my monitors with me in my new big basement. I'm gonna start experimenting hopefully soon and will see if I can incorparate that design. Having a potentiometer is so much nicer.

Where did you find a potentiometer for that voltage?

[Syntax]

Can you post 2 side by side pictures of 0v and -229v but set the brightness level on -229 to match -0v?

I'm interested to see if there is a difference at all.

[LukeEvansSimon]

Uhh, that is some nice work! Very interesting stuff. I'm right in the process of moving and I'm gonna have all my monitors with me in my new big basement. I'm gonna start experimenting hopefully soon and will see if I can incorparate that design. Having a potentiometer is so much nicer.

Where did you find a potentiometer for that voltage?

The pot is rated for up to 250V and 250mW, which is more than enough for this application. I bought it from here. The snap-in knobs for the pot are optional, and come in a variety of designs. If you don't use a snap-in knob, you can just use a plastic alignment tool or screw driver to adjust the pot. I went for the very long dial here so that it could be safely adjusted by hand without a tool.

I also put together a "simple" version of this design, without the pot and ripple filtering. The filtering is overkill, and the pot is unnecessary if you are going to stick with a single setting. As you can see, this simple version is very easy to build, and it does not require adding a new winding to the flyback:


"Flyback-pin" can just be a wire that is soldered to one of the pins on the flyback that has a waveform with a peak to peak voltage of somewhere between 150 and 250 volts peak to peak. R1 limits the current used, especially during powering on. C1 and D1 together create the "new" power supply. C1 is a coupler that provides galvanic isolation and removes the DC bias of the input power, while D1 makes the "new" power supply a negative rail. D2 converts the AC to DC, and C3 removes the noise and smooths the output.

Here is another side-by-side, but since it was taken during the day, the bright sunlight added glare and washed out the colors, especially the blacks.

[LukeEvansSimon]

Can you post 2 side by side pictures of 0v and -229v but set the brightness level on -229 to match -0v?

I'm interested to see if there is a difference at all.

The brightness levels are matched. I used 240p Test Suite's color bars pattern to match the black levels and white levels of both. The decreased light output of the picture on the right is because less phosphor surface area is being illuminated. But you sound like a CRT tech expert, so please enlighten us all on your infinite wisdom as to why you think the brightness levels are not matched.

I'm interested to see if you know anything at all.

[Syntax]

Funny, doesn't look so bright compared to 0v.

Seems like a really involved method of turning the screen brightness down.

That and a waste of time. The 480p thing sounds much more interesting.

[Josh128]

Oh snap!

[anexanhume]

Great work (OP and others). Making a consumer SD set is certainly interesting, but what about making an HD CRT multi sync? It inherently has the video bandwidth, you just have to allow sync rates other than 35kHz to get to the tube, right? The reason I ask is because the 34XBR960 had a display pass through that allows 1080i to propagate through with no lag. If you could hardwire the muxes to always pass through the input signal, theoretically you could make it multi sync, right? Over driving to get it to 720p or even 1080p would be amazing, too.

I’m willing to guinea pig my set for the cause. Would love to mod my 27FV300 too, though I wonder how far back you’d need to modify to support 31khz sync or greater through all the datapaths.

Also, I get that this mod rejuvenates the cathode, but will decreased spot size contribute to acceleration of phosphor aging?

[LukeEvansSimon]

Funny, doesn't look so bright compared to 0v.

Seems like a really involved method of turning the screen brightness down.

That and a waste of time. The 480p thing sounds much more interesting.

Thanks for your scientific analysis about "look so bright" and "turning the screen brightness down". The technical details you have provided are a tremendous gift to the CRT gaming community Honestly though, you clearly have little understanding about the science behind how CRTs work.

[vol.2]

Here is another side-by-side, but since it was taking during the day, the bright sunlight added glare and washed out the colors, especially the blacks.

Spoiler

Even if we have science on paper, the presented result is ultimately an observational one.

If your optimized example looks super dark in comparison to your baseline, it doesn't effectively show the advantage in your technique versus turning down the picture controls to reduce blooming. If the two photos were taken in the same lighting conditions, what does that suggest about the difference in brightness (or not) between the two example photos?

It would really behoove you to have a couple of well take photos of a system paused on a specific screen, with the camera on a tripod and fixed in place on a locked focus and exposure setting, in a dark room.

[ElBartoME]

I also put together a "simple" version of this design, without the pot and ripple filtering. The filtering is overkill, and the pot is unnecessary if you are going to stick with a single setting. As you can see, this simple version is very easy to build, and it does not require adding a new winding to the flyback

That is awesome. I'm gonna build this type of supply the next time I get the chance, although I still suggest putting in the potentiometer. That makes my life so much easier. I hated playing around with the number of turns of the winding.

That makes it also possible to change the spot size "on the fly" more or less.

It would really behoove you to have a couple of well take photos of a system paused on a specific screen, with the camera on a tripod and fixed in place on a locked focus and exposure setting, in a dark room.

I like that idea. When I have my "lab" set-up I will use a tripod to make pictures with different with the lights off at night. Most of the Sony consumers I modded keep the brightness constant when I change G1 and G2. But I'm still gonna verify the brightness.

[LukeEvansSimon]

Here is another side-by-side, but since it was taking during the day, the bright sunlight added glare and washed out the colors, especially the blacks.

Spoiler

Even if we have science on paper, the presented result is ultimately an observational one.

If your optimized example looks super dark in comparison to your baseline, it doesn't effectively show the advantage in your technique versus turning down the picture controls to reduce blooming. If the two photos were taken in the same lighting conditions, what does that suggest about the difference in brightness (or not) between the two example photos?

It would really behoove you to have a couple of well take photos of a system paused on a specific screen, with the camera on a tripod and fixed in place on a locked focus and exposure setting, in a dark room.

For CRTs, "brightness" refers to black level calibration, which is only one component of 3 determining factors for total light emission from a CRT. White level calibration and spot size are the other two determining factors. If all you did was turn brightness down, you'd crush all of your shades of grey into black, and all dark shades of green, blue, and red (as well as all variations of them), would be crushed into black.

To understand why "brightness" is the wrong term, consider a pixel pattern that is a single dark red pixel on an entirely black background. Turning the brightness down would make the pixel disappear (crush into black). This mod does something different, it decreases the size of the area of phosphor that is illuminated when drawing the pixel, but the illuminated area is still the same dark shade of red and it is still visible. It is true that the photon flux density for the CRT screen's face is reduced by this mod, and the photon flux density is also reduced by turning the brightness down. But they are two different things that alter the picture in two different ways.

People often misunderstand the difference between black levels (brightness), white levels (contrast), and photon flux density (total light emission).

[maxtherabbit]

Here is another side-by-side, but since it was taking during the day, the bright sunlight added glare and washed out the colors, especially the blacks.

Spoiler

Even if we have science on paper, the presented result is ultimately an observational one.

If your optimized example looks super dark in comparison to your baseline, it doesn't effectively show the advantage in your technique versus turning down the picture controls to reduce blooming. If the two photos were taken in the same lighting conditions, what does that suggest about the difference in brightness (or not) between the two example photos?

It would really behoove you to have a couple of well take photos of a system paused on a specific screen, with the camera on a tripod and fixed in place on a locked focus and exposure setting, in a dark room.

For CRTs, "brightness" refers to black level calibration, which is only one component of 3 determining factors for total light emission from a CRT. White level calibration and spot size are the other two determining factors. If all you did was turn brightness down, you'd crush all of your shades of grey into black, and all dark shades of green, blue, and red (as well as all variations of them), would be crushed into black.

To understand why "brightness" is the wrong term, consider a pixel pattern that is a single dark red pixel on an entirely black background. Turning the brightness down would make the pixel disappear (crush into black). This mod does something different, it decreases the size of the area of phosphor that is illuminated when drawing the pixel, but the illuminated area is still the same dark shade of red and it is still visible. It is true that the photon flux density for the CRT screen's face is reduced by this mod, and the photon flux density is also reduced by turning the brightness down. But they are two different things that alter the picture in two different ways.

People often misunderstand the difference between black levels (brightness), white levels (contrast), and photon flux density (total light emission).

The bottom line is regardless of the correct terminology nobody cares if it looks darker they will say it's darker. Instead of getting mired in the wording you should respond to his actual point

[LukeEvansSimon]

The bottom line is regardless of the correct terminology nobody cares if it looks darker they will say it's darker. Instead of getting mired in the wording you should respond to his actual point

I am pretty sure I have responded, multiple times, to the following incredibly insightful statements: (1) this is the same as turning down the brightness, and (2) this is the same as tuning the focus pot on the flyback.

[Blacksheep]

The bottom line is regardless of the correct terminology nobody cares if it looks darker they will say it's darker. Instead of getting mired in the wording you should respond to his actual point

I am pretty sure I have responded, multiple times, to the following incredibly insightful statements: (1) this is the same as turning down the brightness, and (2) this is the same as tuning the focus pot on the flyback.

How about, instead of posting cocky replies to legitimate queries, actually responding to the points made? All the science in the world is not going to help you if the end result is ultimately not worth the hassle.

Actually turn down brightness and show us that it's not the same. Make a video in a dark room using a tripod, mention which camera you're using and the settings. Slowly turn the pot towards -229V starting from the 0V initial position. Can't be that hard.

Also it's still unproven that you're increasing TVL. Do the honorable thing, change the title.

[LukeEvansSimon]

How about, instead of posting cocky replies to legitimate queries, actually responding to the points made?

I have responded several times to several different people that pop into this thread and claim "this is the same as turning the brightness down" or "this is the same as changing the focus pot". So whenever somebody pops into this thread and adds their cocky reply along one of those two statements, they will get a cocky reply back.

[vol.2]

So whenever somebody pops into this thread and adds their cocky reply along one of those two statements, they will get a cocky reply back.

That didn't happen. I brought up a flaw (that you qualified in your own post by saying your room was too bright) in your photographic comparison and suggested a way to address it. I never made either one of those statements.

I was hoping to help you bring a more positive environment to you thread and to dispel some of the trolling and negativity, not to argue with you about the merits of your project.

I wish you all the best.

[matt]

Come on everybody, please don't get personal. This is a fascinating topic and I'd hate to see the discussion get thrown out because we have disagreements on minor details.

Whether or not the original mod was successful in increasing a TV's TVL rating, it seems like the OP and others are trying to make progress in that direction through other means and IMO the thread title is still appropriate.

[SuperSpongo]

vol.2 I don't think he was addressing your post, but rather Syntax's.

And I agree, I really hope the constant naysayers don't push Luke to completely abandoning the project or at least stop posting his findings here. That would be a shame.

[ElBartoME]

That didn't happen. I brought up a flaw (that you qualified in your own post by saying your room was too bright) in your photographic comparison and suggested a way to address it. I never made either one of those statements.

That is constructive criticism the way I like it. You made a valid point and gave a suggestion how to fix it.


But the pages and pages of (sometimes in my opinion pointless) discussions made me also tired to work on this topic or share my results.
Everytime the thread dies down and Luke comes back with some new findings there is new drama.


I made this picture some time ago in a dark room. Without a tripod though. They both should be at the same brightness, but next time I'm gonna make some pictures with a tripod and make sure the brightness is constant.

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

[FinalBaton]

I will say, even if this mod is not for me (I prefer softer RGB picture),

it did teach me something (spot size) and I'm thankful for that

and I hope it'll keep going because even if it doesn't interest me, it might interest other people

[tomato16]

Thanks for all your hard work Luke.

I am interested in trying this on a KV-20S10. I would like to add a switch to make it easier to take before/after photos.

Would something like this work?

[incrediblehark]

Just wanted to say I appreciate the work you’ve put into this, and I enjoy reading all of the technical information written, even though a lot of it is over my head. I hope that your findings will one day be able to unlock the potential of my D-series to become a 36” multisync monitor. Not that I have the skills to do it myself

Looking forward to seeing more pics as well!

[smorsked]

This thread looks very promising. I want to try to adjust G1 voltage to my Sony KV-A2943E scart Trinitron. With thinner scanlines it would be my dream crt. It has the same tube as the KV-29X5E wich people seem to love on these forums.
My question is about how to connect the G1 pins in the case where you have three G1 pins. on my KV-A2943E there are three pins, G1-1, G1-2 and G1-3 all of them are just grounded. Should I cut the three traces and connect all of them to the DIY powersupply or just one of them? Does the circuit change in any way because there are three pins?

Any help is much appreciated <3

[antorsae]

Thank you so much for posting the experiments and results.

I have a few questions:

1. Did anybody had any luck changing the neck transistors with others w/ more bandwidth?

2. Re: G1 mod (screen-adjusted), I don't want to beat a dead horse, but it is still unclear to me (difficult to see in pictures) how the peak brightness (as measured herehttps://www.displaymate.com/ShootOut_Part_1.htm with 100% full IRE field, e.g. in cd/m2) compares to unmodded G1; and if it would be possible to amplify the RGB signals a bit more to achieve higher peak brightness (again, properly calibrating black level, etc.).

While getting more peak brightness is in principle unrelated to the G1 mod, the thick spot size of unmodded G1 would be even higher and thus less desirable.

In many SONY consumer sets you can set the drives of each channel from service menu, and the service manual lists different values for 25" and 29" sets:



while the neck boards are equal for 25" and 29" models:



Regards.

[LukeEvansSimon]

Thanks for all your hard work Luke.

I am interested in trying this on a KV-20S10. I would like to add a switch to make it easier to take before/after photos.

Would something like this work?

What is the peak to peak voltage of that flyback pin? 200Vpp? The switch is fine, but the pot should not go there. It should be placed after C3, and another decoupling capacitor is then required after the pot. Regarding the neckboard, it is not clear to me what the trace attached to G1 connects to on that neckboard. If you cut the trace, then your design will work.

[LukeEvansSimon]

During my reading, I bumped into this patent from Intel on CRT design that describes what the G1 biasing grid does, and it made me think of this thread. So I thought I'd post an update.


I haven't touched this project since May. I fell down the rabbit hole of non-solid state TVs, that is, TVs that use more than just one vacuum tube. I have been studying classic CRT research articles, such as the collected works of: RCA's Zworykin, RCA's Grob, and RCA's Schade. Non-solid state CRT displays are significantly more simplistic than solid state CRT displays, and I am developing a from-scratch all new old stock vacuum tube YPbPr video monitor that uses a new old stock "M-class" fine dot pitch CRT and several vacuum tube diodes, triodes, and pentodes. It is very satisfying to get down to the core circuits of a CRT display like this. Solid state CRTs are great, but they use very complicated circuits with many black box "jungle" ICs. Vacuum tube rectifier, amplifier, and oscillator circuits are very simple and elegant. It is like an entire circuit built out of little CRTs.

Back to the G1 mod: I realize that I did not post pictures of the final mod, so here they are...


I ended up adding RLC filters before and after the potentiometer. These filters only made minor improvements to the video quality, but the oscope showed a very good improvement in G1 voltage stability, so I left them in the final build just in case. The G1 to cathode voltage is more stable after the mod than before! Note: R4 and R5 simulate the wires that connect the G1 control PCB to the neckboard. They are not discrete resistors!


The final G1 control board is tiny. If anybody is interested, I will post a parts list. I used 3M adhesive standoffs to fix the board inside the TV. The pot has an extra long dial so you can safely adjust it without an extra tool.


The neckboard already had solder holes for a bus wire that connected the G1 trace to ground. So I removed the bus wire and replaced it with two quick disconnect terminals. This way the mod can be unplugged from the neckboard via wires that have quick disconnects on both ends.


The 27-inch TV I modded has lots of empty space inside. The G1 controller board easily fit in the empty space next to the flyback transformer. This allows the G1 G2, and G3 potentiometers to all be easily accessible in the same area of the back of the TV, with 3M adhesive standoffs gluing it in place.





I found this side-by-side comparison on my phone from May. The pictures of Alucard from SotN are not in the same area of the map, so ignore the background pixels. You can see the spot size is much smaller after the mod, but the camera photo picks up a moire effect. The moire effect is hardly noticeable in real life, but for some reason when zoomed in with my iPhone, the moire effect is exaggerated. I have noticed that my iPhone exaggerates the moire effect of other CRTs, even ones not modded. However, this does bring up a real limitation of this mod. As spot size gets very small, moire effect becomes more and more noticeable. However, you can use the potentiometer to adjust the spot size to a point where moire is not noticeable in real life, yet the spot size is sharp. If you make the spot size too small, then moire becomes noticeable, even in real life. The fact that aperture grille CRTs do not have a horizontal masking of the phosphor like slot mask means the moire effect on an aperture grille will be less pronounced.

[buttersoft]

Yes, parts list please!

And, because i'm nowhere near your level on this, and because i'm tired of reading through Syntax's delightful, not-at-all-pathological commentary, can you give a clearer diagram showing how to wire the mod into your average consumer CRT? Does it still need winding around the exposed core of the flyback? What are Vin and Vout? etc...

If you don't want to bother doing that, i guess i'll have to work it out. Either way, thank you for posting again I'm keen to hear how your other projects get on as well.

[SuperSpongo]

Amazing work! I was thinking about this mod the other day, talking with ElBartoME and saw your other posts on reddit. I feared that you got fed up with posting here so I'm glad you came back with an update.