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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Thu Feb 04, 2021 11:57 pm 



Joined: 28 Nov 2019
Posts: 71
Derf wrote:
Blacksheep wrote:
Seconded, thanks for doing that ElBartoME. Are you able to display the pattern in the correct aspect ratio? Might warp the result otherwise.

It does look like the squares aren't square and circles aren't circle. He's using CRT emudriver so he can plug in any custom resolution. The picture needs to be cropped to that resolution too I believe.


Especially the second picture.

Output resolution itself shouldn't affect the resulting aspect ratio of the picture, but I don't know how the signal is generated in ElBartoME's case exactly. Maybe there can be some additional translation. I would choose a sufficiently high output resolution, and then adjust the picture on the display until aspect ratio is correct.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Fri Feb 05, 2021 12:05 am 



Joined: 07 Aug 2018
Posts: 63
I chose 1024x480 because the horizontal resolution of that picture is 1024. I can't to higher than 480 with the vertical resolution though so this will show a warped picture. But my goal was to have the picture show up in the original horizontal resolution.

I'm using CRT emudriver. Anybody has a suggestion of a resolution I should use? The picture has a 1024x791 resolution.

I'll upload the future pictures as PNG.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Fri Feb 05, 2021 12:09 am 



Joined: 28 Nov 2019
Posts: 71
Ok, thanks. You should be able to display it in the correct aspect ratio by adjusting the display (V SIZE / H SIZE I believe). The EIA 1956 resolution chart is 4:3 and circles are circles / squares are squares, so that's how it should be displayed. Is there a vector version (.svg) of the EIA 1956 resolution chart, or similar? Would be ideal, but not necessary.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Fri Feb 05, 2021 12:17 am 



Joined: 07 Aug 2018
Posts: 63
I'll change the vertical size to get a square image. But that won't really change anything with the TVL as that is measured horizontally.


There is a svg here: https://commons.wikimedia.org/wiki/File ... t_1956.svg
But somehow the text is missing. Also the resolution is different (990 x 765)....so which one should I use? It seems weird that the resolution is different.

Oh btw the chart will be cut off at the top and bottom because I'm displaying it at 100% zoom and I can only show 480 lines of it.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Fri Feb 05, 2021 12:27 am 



Joined: 28 Nov 2019
Posts: 71
Thanks, that .svg is excellent. See, the EIA 1956 resolution chart has no resolution. It was printed/painted onto a carrier medium and filmed. We have to get away from all this resolution talk, as it just serves confusion when talking about TVL.

ElBartoME wrote:
I'll change the vertical size to get a square image. But that won't really change anything with the TVL as that is measured horizontally.


At least horizontal size makes a difference for TVL: if the picture is squished horizontally, then the vertical lines are closer together. You can change vertical size, but if the 4:3 chart doesn't fit the 4:3 screen then the TVL reading will be off anyway.

ElBartoME wrote:
But somehow the text is missing. Also the resolution is different (990 x 765)....so which one should I use? It seems weird that the resolution is different.


We don't need the text. An .svg has no resolution.. it's vector graphics. You can losslessly generate any resolution you'd like out of that.


Last edited by Blacksheep on Fri Feb 05, 2021 12:34 am, edited 1 time in total.

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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Fri Feb 05, 2021 12:34 am 



Joined: 07 Aug 2018
Posts: 63
Thanks for the clarification!

Yes, I'll definitely fill the entire screen horizontally.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Fri Feb 05, 2021 1:33 am 



Joined: 17 Aug 2020
Posts: 113
ElBartoME wrote:
Thanks for the clarification!

Yes, I'll definitely fill the entire screen horizontally.


It will be awesome to use a TVL test pattern to measure any TVL improvements. As I mentioned earlier in this thread, I have been experimenting with CRT cathode amplifier circuits because bandwidth limitations in the chroma signal path to the cathodes, in theory, will limit the achievable TVL. With a digital oscope and a TVL test pattern, you can easily see what the effective TVL of the chroma signal path is by displaying the TVL test pattern on the CRT and then use the oscope to capture the cathode voltage waveform.

To do this, you need to first measure the cathode voltage of a pure white screen and a pure black screen, as well as the voltage level used for clamping the cathodes to "blacker than black" during horizontal retrace. Then switch to a test pattern that is alternating vertical white and black lines from top of the screen to the bottom. It is important that each row of the test pattern is identical to make locking the oscope trigger to a single horizontal line of video as easy as possible.

You then set the probe trigger on the upward edge of the horizontal blank that is applied to the cathodes during the horizontal retrace time between each line of video. The chroma signal for each cathode is clamped higher than the voltage used for black during this time, so triggering on that upward edge will allow you to easily align one line of video, and since each line of video is alternating white and black pixels (to draw a bunch of vertical lines), you don't have to worry about catching the right line of video, any line will do.

As the number of alternating white and black vertical lines is increased and the bandwidth requirement on each stage of the chroma signal path is increased. For RGB video signals, the bandwidth can be bottlenecked by the video pre-amp, which for many CRT TVs is in the jungle chip, but since the video pre-amp doesn't have to do much work, the most likely bottleneck will be the cathode amplifiers on the neck board. Pre-amps need to amplify a signal from around 1VPP to around 2 to 5VPP. Not that hard to do, even at high video bandwidth. The cathode amps need to take a 2 to 5VPP signal and amplify it to around 200VPP signal (for CRT TVs and arcade CRTs). Pro CRTs use around 50 to 100VPP for their cathodes due to the electron guns being designed for lower voltage.

So as the chroma signal path is reached, the peak to peak voltage of the cathodes will not be from the voltage of a pure white screen to the voltage of a pure black screen, but instead the peak to peak voltage will shrink to the point where the cathodes are only pulled high enough to output dark grey and low enough to output light grey. The CRT will look like the vertical lines are blurring together, but the bottleneck is not dot pitch or spot size... but instead it is chroma signal amplifier bandwidth limit.

When the chroma signal bandwidth limit is not a bottleneck, the oscope will show X peaks and X troughs corresponding to the X black and X white vertical lines, and the voltage of the peaks will be hitting the voltage of a black screen... and the voltage of the troughs will be hitting the voltage of a white screen.

TLDR: Alternating white and black vertical lines is the highest bandwidth test pattern due to the fact that CRTs draw each frame as a series of horizontal rows, and so chroma signal bandwidth can be a limiting factor. So make sure to oscope your cathodes to see how much that bottlenecks achievable TVL.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Fri Feb 05, 2021 11:20 am 



Joined: 07 Aug 2018
Posts: 63
LukeEvansSimon wrote:
It will be awesome to use a TVL test pattern to measure any TVL improvements. As I mentioned earlier in this thread, I have been experimenting with CRT cathode amplifier circuits because bandwidth limitations in the chroma signal path to the cathodes, in theory, will limit the achievable TVL. With a digital oscope and a TVL test pattern, you can easily see what the effective TVL of the chroma signal path is by displaying the TVL test pattern on the CRT and then use the oscope to capture the cathode voltage waveform.


That is a good idea. I'll hook up an oscilloscope to one cathode and I'll also create a python script to generate a testpattern with alternating lines.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Fri Feb 12, 2021 10:04 pm 



Joined: 17 Aug 2020
Posts: 113
This mod is likely very effective at prolonging the life of a worn-out CRT. Under normal use, a CRT’s cathodes slowly wear away. The cathodes emit the cathode ray that is used to draw the screen, and when new, the cathode ray is produced by the sharp tips of the cathodes. Eventually the tips run out of electrons to emit, and the contrast and brightness settings need to be increases in order to force the cathodes to continue to emit electrons. When this is done, the electrons no longer come from the sharp tip of the cathode, but instead, the electrons come from the sides of the cathode. This causes the cathode ray beam to be thicker and the spot size on the screen is larger too. The resulting image quality is less sharp.

As the wearing process continues to get more extreme, the cathode amplifier ICs on the neckboard struggle to properly cutoff the flow of electrons when the image transitions from bright to very dark colors. This causes the image to smear and streak from left to right. The cathode amplifiers have to work harder because when contrast is maxed out to keep the screen from being too dim, the amplifier gain is pushed to its limit where the transistor’s rise and fall times are slowest. In addition, when brightness is maxed out, the cathode cutoff voltage is no longer achievable because it is beyond the peak voltage the amplifier can output. This mod fixes smearing and streaking in this situation because making the G1 anode’s voltage more negative decreases the peak voltage the amplifier needs to output to cutoff the cathode ray from flowing towards the screen.

The other two techniques for rejuvenating a worn out CRT are: (i) super heating the cathodes so as to reflow the election emitting materials towards the tips of the cathodes, and (ii) increasing heater voltage to increase electron emission from the cathodes.

Adding this mod as a third CRT rejuvenation option means CRT gamers will have more options for continuing this hobby for decades to come.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sat Feb 13, 2021 1:02 am 



Joined: 07 Aug 2018
Posts: 63
That is exactly what I was seeing. I was able to get a much better picture out of a worn tube after applying this mod. I also saw that streaking and it was gone with the proper G1 voltage. This is a much better option of extending the life of the tube in comparison to rejuvenation in my opinion.

I wasn't able to do the TVL tests yet but I hope to do that soon though.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sun Feb 14, 2021 4:32 am 


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I'm curious - with TVs where the G1 voltage is positive (some Trinitrons seem to be this way), how much of a difference would it make to connect the G1 straight to chassis ground? If it's enough to help with streaking on older tubes, this would be a quick & dirty way to improve a TV's picture without going to the trouble of setting up another power supply.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sun Feb 14, 2021 10:40 am 



Joined: 07 Aug 2018
Posts: 63
Some olders chassis have G1 at around 20V to 30V. Even the PVM-2730 (which I will mod soon as well) has it at that voltage.

Putting it at ground would only make a slight difference though. I'm not sure if you would be able to tell the difference. With these chassis I found out though that you can't go that negative as with other chassis that have their G1 at GND. On my A3411D that had a 30V on G1 I could only go to -90V. With the E3431D or 29X5D I could go to -130V.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sun Feb 14, 2021 11:41 pm 


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ElBartoME, I'd be keen to hear how you get on with the PVM-2730 - i have a few of those.

Definitely looking forward to the new generic neckboard design as well!


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Wed Feb 17, 2021 7:59 am 


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I read the entire thread before jumping in. I stay out of mod threads being a non-modder but I didn't appreciate the Reddit post in crtgaming boasting about boosting the TVL. Reddit knowledge level is far lower than here. That's also disingenuous to compare the spot size on Mega Man using non-PVM to PVM and imply your mod makes the image look like the PVM's with its higher quality phosphors. SamIAm explained in different terms. As impressive as your analysis is to solve red color bleeding by adjusting the cutoff voltage in the service menu, you don't warn anyone on page 1 that they'll need to do this and not all CRTs have that ability.

Josh128 straight out told you that he didn't count more TVLs in pre-mod and post-mod pics and you defended yourself by re-defining "TVL" from the definition actually used to sell PVMs and adopted by everyone in retro gaming who then re-sell PVMs. Addressability vs resolution is interesting and scientific but you mention neither when start by saying you increase TVL and show calculations of how 1000 TVL is achievable. We had heavyweights mikejmoffitt and 6t8k weigh in expertly as well and no one scrolling to the last page will see that. Last thing I want here is someone selling a "TVL boosting" mod service on an already rare and expensive PVM and damaging it.

The explanation of increasing CRT lifespan confuses me. You're making the screen less bright with negative G1 voltage and increasing G2 voltage to compensate. Image still looks dim so you're turning the brightness and contrast knobs up to compensate? Doesn't that increase the cathode voltage and work of the RGB amplifiers? But G1 < 0 reduces the level needed for cutoff for true black so that is an advantage. You don't mention the cutoff voltage changes for R, G and B. I think the average cathode voltage level would be higher since there is more luminance than darkness in most video games.

I don't blame you for showing spot size in green, the most luminant color. Red is second highest and blue the least. Would be more fair to show each color, or at least one image each high in R, G and B to verify bleeding is minimized and convergence is good. That is one thing you and ElBartoME very fairly point out that convergence issues are more noticeable with smaller spot size. It just doesn't get edited onto page 1 for everyone to see.

Quote:
CRT flybacks have an exposed core. If you loop a wire around that exposed core about 125 times, then the voltage between the ends of the wire will be 250 volts. The current is extremely low, but that is a good thing because the G1 does not need a high current.


Making a -250 voltage source that way, [voltage] = [current] * [resistance] = -[area perpendicular to the magnetic field] * [change in magnetic field with respect to time] => emf = i * R = -N * dB/dt. As you add a turn N, for more area on the way to 125, you increase R by the equivalent cable length, thus current is constant despite more voltage. You increase voltage with constant current and therefore increase power linearly. Power for G1 and higher voltage and therefore higher power for G2 don't come from nothing. Are you not straining the flyback transformer and reducing its lifespan and heating the nearby components? Running G1 and G2 higher than what they're rated for? I don't know how the deflector part of a CRT works but the electrons hitting it have much more force by than they're supposed to by F = q * v X B, where X is the cross product and the higher G2 increases v, the velocity vector.

I would think then that you're reducing the lifespan of the CRT more than increasing it.

I'm done being mean.
------------------------

I do give you credit for mentioning to add the capacitor to reduce ripple voltage. Ripple voltage is not DC and is lost as heat. I could show the math to calculate and estimate it and the minimum capacitance needed since I don't think everyone attempting this mod is going to have an oscilloscope or know how to use LTspice.

I also give you a great amount of credit for constructing SPICE simulations of a mod. Sets a new standard when I can't think of another mod that does this. I sometimes wonder where new resistor and capacitor values come from. Thin air or first thing that works?

I actually think the math on page 1 is fascinating for theoretical minimum TVL and I learned quite a bit. I want to contribute one source I found on CRTs that starts on page 3: https://www.scribd.com/document/494829098/CRT-Information

My understanding from this mathematics book for programming excerpt is that the negative G1 voltage reduces the number of electrons that come out of the electron gun. More negative, fewer electrons, so lesser intensity, so lower brightness. I get that from a geometric argument an outer ring of negative voltage pushes the electrons closer together as they approach the iris but then wouldn't the positive voltage G2 ring, of much greater magnitude, spread them apart? I think the reduced electron count is far more significant for the smaller spot size. Not that it changes anything.

Quote:
The prominent scanline look is something gamers are interested in.


I have a different opinion. We know the classic divide was increase RF + composite blurring in consumer CRTs to reduce flicker and increase scanlines on professional CRTs so broadcaster could judge tendency of flicker.

In my childhood RCA CRT, I could see the faint scanlines and they ended up being extremely important in one SNES game to count the value of the player's reputation. I don't need thick or thicker scanlines, that minimal amount is enough and LCD smoothening between horizontal lines looks like hot garbage in comparison. My 20L2 has unsurprisingly thicker scanlines than my consumer JVC 20F703, except I noticed JVC's are thicker for S-Video. Maybe I need to adjust settings but that took me by surprise.

For horizontal resolution, I didn't see anyone talk about accuracy of the image. SNES native resolution is 256×224 (8x7), right, with a few games using 512x448 as someone mentioned. CRT stretches that. My 600 TVL PVM gives a more accurate (4:3) scaling than consumer low TVL and I see that borne out in the images here. Making smaller dots doesn't help in and of itself. Maybe you can take a CRT that uses 2 triads / RGB groups per pixel and change G1 and G2 to yield 1 triad per pixel and achieve better scaling. No black line separating the 2 for higher TVL by PVM salesman definition but I don't think you'd encounter much resistance if you claimed it. What I'm not sure is if 1.2, 1.5, etc. triads per pixel down from 2.0 is actually better for video games that never went above 480 / 525 horizontal resolution.

Also curious about PAL. Abomination that it may be for 50 Hz, the alternating phase of the lines, thus the acronym, on half the chroma signal reduces noise in theory. Shouldn't composite and S-Video look better and therefore benefit more from this mod?


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Wed Feb 17, 2021 10:37 am 



Joined: 07 Aug 2018
Posts: 63
NewSchoolBoxer wrote:
The explanation of increasing CRT lifespan confuses me. You're making the screen less bright with negative G1 voltage and increasing G2 voltage to compensate. Image still looks dim so you're turning the brightness and contrast knobs up to compensate? Doesn't that increase the cathode voltage and work of the RGB amplifiers? But G1 < 0 reduces the level needed for cutoff for true black so that is an advantage. You don't mention the cutoff voltage changes for R, G and B. I think the average cathode voltage level would be higher since there is more luminance than darkness in most video games.


It depends on how you define CRT lifespan. I was specifically talking about the tube itself, not the electronics. My A3411D for example had the problem of severe spot size blooming with higher contrast to the point that the scanlines would blur into each other. At this point I would discard that TV as using it for gaming is not fun for me. After I changed G1 to -90V the spot size blooming got a lot better. Also I didn't need to crank up the brightness and contrast values as going up with G2 was enough have the brightness constant.

On my E3431D I noticed the picture cutting out completely when I made G1 more negative without raising G2. The picture brightness was constant when I slowly made G1 more negative. I assume the jungle chip was adjusting brightness and contrast internally to achieve a constant image brightness. That would put more strain on the amplifiers. What I did is to raise G2 almost to the end of the potentiometer and dial it back a bit. I set G1 then to a voltage 20V before the image would cut out. That's how I got to a G1 voltage of -120V.

Next time I'm working on my E3431D and doing the TVL tests I'm gonna also measure the cathode voltages with a G1 of 0V and -120V and see how much more the amplifiers really need to work.

NewSchoolBoxer wrote:
Making a -250 voltage source that way, [voltage] = [current] * [resistance] = -[area perpendicular to the magnetic field] * [change in magnetic field with respect to time] => emf = i * R = -N * dB/dt. As you add a turn N, for more area on the way to 125, you increase R by the equivalent cable length, thus current is constant despite more voltage. You increase voltage with constant current and therefore increase power linearly. Power for G1 and higher voltage and therefore higher power for G2 don't come from nothing. Are you not straining the flyback transformer and reducing its lifespan and heating the nearby components? Running G1 and G2 higher than what they're rated for? I don't know how the deflector part of a CRT works but the electrons hitting it have much more force by than they're supposed to by F = q * v X B, where X is the cross product and the higher G2 increases v, the velocity vector.

I would think then that you're reducing the lifespan of the CRT more than increasing it.


The current going in or out of G1 should be very small. That voltage is only used to charge G1 to a negative level to repel the electrons. There are no electrons flowing in or out of G1 to produce any significant current. But I still put a series resistor of 330 Ohms where I can measure the current. I will also do that next time.

And yes, you are right. The resistance of the turns will increase with the cable length. But that resistance is not what determines the current flow. There is nowhere for the current to go from the G1 plate. Therefore the strain on the flyback should in theory be small. But as I said I will check that.

I really don't know where the number 125 comes from. I get around 7V per turn on the Sonys I worked on.

I'm not running G2 beyond its rating. I didn't do any modifications to raise G2 outside the specs. I just use the screen potentiometer.

NewSchoolBoxer wrote:
I have a different opinion. We know the classic divide was increase RF + composite blurring in consumer CRTs to reduce flicker and increase scanlines on professional CRTs so broadcaster could judge tendency of flicker.


Of course that is a matter of opinion. Some people like the look of lower TVL screens where the scanlines are almost thick enough so no space can be seen between them with 240p. Others like the extreme sharp look of a 1000 TVL screen where the black space between the scanlines are basically thicker than the illuminated parts.

I personally fall into the latter category, altough the 1000TVL screen of my D24 sometimes is too much for 240p. That's why I'm a huge fan of the mod. I can mod my 34 inch consumer to have more defined scanlines and have the look of higher TVL screens on a much bigger screen even if it does not increase TVL.


Last edited by ElBartoME on Thu Feb 18, 2021 8:29 am, edited 1 time in total.

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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Thu Feb 18, 2021 3:02 am 



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Posts: 113
NewSchoolBoxer wrote:
As impressive as your analysis is to solve red color bleeding by adjusting the cutoff voltage in the service menu, you don't warn anyone on page 1 that they'll need to do this and not all CRTs have that ability.


The varying cutoff voltages per color is mentioned in my original post, specifically it is mentioned in one of the references that I provide.

NewSchoolBoxer wrote:
Josh128 straight out told you that he didn't count more TVLs in pre-mod and post-mod pics and you defended yourself by re-defining "TVL" from the definition actually used to sell PVMs and adopted by everyone in retro gaming who then re-sell PVMs. Addressability vs resolution is interesting and scientific but you mention neither when start by saying you increase TVL and show calculations of how 1000 TVL is achievable.


I don't have a time machine, so the journal articles from 20 to 40 years ago, which I referenced in the original post, where the difference between "addressability" and "resolution" is defined... that was the CRT research community defining terms in that way, literally decades ago! I did not define these terms. I did not make this up, but merely referenced the terminology as it was used by the people that researched and designed CRTs, back when they were the leading display technology. The gaming community is the one that redefined terminology for resolution, similarly to how Sega made up terms such as "blast processing" to describe the higher CPU clock rate the Sega Genesis (aka Megadrive) operated at.

The difference between these two terms is important, because if you understand why decades ago, the CRT R&D field considered it important enough to distinguish between "addressability" and "resolution", then you will understand why Josh128's point was meaningless. Using my Playstation 1 set up as an example, this mod does not change the number of lines of video that the PS1 addresses, but instead, this mod changes the number of lines of video that the CRT can resolve, without them blurring together.

NewSchoolBoxer wrote:
We had heavyweights mikejmoffitt and 6t8k weigh in expertly as well and no one scrolling to the last page will see that.


This is a logical fallacy known as argumentum ad verecundiam. Regardless, mikejmoffitt ended up experimenting with this mod to great success (details here).

NewSchoolBoxer wrote:
The explanation of increasing CRT lifespan confuses me. You're making the screen less bright with negative G1 voltage and increasing G2 voltage to compensate. Image still looks dim so you're turning the brightness and contrast knobs up to compensate? Doesn't that increase the cathode voltage and work of the RGB amplifiers? But G1 < 0 reduces the level needed for cutoff for true black so that is an advantage. You don't mention the cutoff voltage changes for R, G and B. I think the average cathode voltage level would be higher since there is more luminance than darkness in most video games.


This mod is used to extend the number of hours you can use a CRT, where the main limiting factor on usable CRT hours is due to the cathode ray emitting layer of the cathodes wearing away. As the barium layer on the cathodes wears away, it first wears away at the tips of the cathodes. This causes the image to be more dim because cathode ray emissions are reduced. To compensate, the user will typically "increase the brightness" by increasing the voltage differential from the G2 anode to the cathodes by increasing the screen voltage pot on the flyback. This causes the electrons that make up the cathode ray to be emitted, not from the tip of the cathode, which no longer has enough electrons to emit... instead this higher screen voltage causes the electrons to be emitted mostly from the barium layer on the sides of the cathode. So while this corrects for the image being two dim, it introduces two issues: (i) the cathode amplifiers need to operate at a higher voltage gain so that black levels are calibrated, and (ii) the shape of the cathode ray is significantly wider because the cathode ray diameter starts off the size of the diameter of the cathodes as opposed to it being the diameter of a small region at the very tip of the cathodes as happens on a new CRT. The first issue manifests as either a washed out picture (because cutoff voltage levels are not achievable), or the issue manifests as streaking (because the amplifier circuit has a lower rise times at the higher voltage). This mod compensates for the first issue by using a more negative G1 voltage to restore black levels, without having to increase the voltage gain that the cathode amps operate at. This mod compensates for the second issue by using the G1 electro magnetic field to squeeze the cathode ray into a tighter shape, as opposed to relying on the cathode ray starting off tight due to emissions coming from a sharp tip of a cathode.

If you look at earlier CRT circuit designs, before advances in transistor amplifier technology, the cathode amplifier circuits were not capable of operating at the high voltages found in later CRT designs. So how did the CRTs achieve voltages high enough for cutoff? They negatively charge the G1 anode so that lower cathode cutoff voltages were sufficient for hitting black levels. The same principle is at play here for using this mod to repair worn out CRTs.

NewSchoolBoxer wrote:
I would think then that you're reducing the lifespan of the CRT more than increasing it.


With this mod, the amount of current that flows into the G1 anode is very small and for a very short duration. Once the G1 anode is charged, no current flows anymore. In other words, the increased load on the flyback is negligible, and the flyback is not used out of spec. But you are missing the point of using this mod to extract more hours out of a CRT. We are talking about using this mod on a CRT with so many hours on it, the image is dim, blurry, and streaking occurs. The best way to fix this problem is to cut the neck of the CRT, replace the cathodes, melt the neck back, re-vacuum the CRT. The last shop that was capable of doing this closed 13 years ago! So up until this mod, that left people with re-surfacing their cathodes using a "CRT Rejuvenator". I own a BK 490b CRT Rejuvenator, and I have tested it on a worn tube. It works, but it is much more invasive than this mod as it super heats the cathodes, burning away the dead layer on the cathode tips and liquifying new barium so that it flows to the cathode tips. If you aren't lucky, the super heating does more damage.

If you have a better idea for getting more hours out of a high hour CRT, please share them here.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Thu Feb 18, 2021 5:20 am 


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another hater gets worked by based OP


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Thu Feb 18, 2021 8:08 am 


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I don't like the "high TVL" look either - I grew up with consumer TVs and Amiga monitors where the scanlines were nice and fat, the blank lines barely visible, and the picture was nice and bright. But, this mod is very appealing if it can extend the life of a tube. I have a couple of TVs that I really like but are clearly starting to wear out, and I'd be stoked if the G1 voltage mod can be used to get a few more years of life out of them in a relatively non-destructive way. Once these tubes are gone, they're gone.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Thu Feb 18, 2021 9:54 am 



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LukeEvansSimon wrote:
So up until this mod, that left people with re-surfacing their cathodes using a "CRT Rejuvenator". I own a BK 490b CRT Rejuvenator, and I have tested it on a worn tube. It works, but it is much more invasive than this mod as it super heats the cathodes, burning away the dead layer on the cathode tips and liquifying new barium so that it flows to the cathode tips. If you aren't lucky, the super heating does more damage.


If anyone's interested in seeing this, check out this German video of an old TV technician showing the rejuvination of a CRT. Starting at ~10 minutes for a B/W tube and ~16 minutes for a color tube.

https://www.youtube.com/watch?v=MUGOzG6MEZQ


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Thu Feb 18, 2021 5:15 pm 



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SuperSpongo wrote:
LukeEvansSimon wrote:
So up until this mod, that left people with re-surfacing their cathodes using a "CRT Rejuvenator". I own a BK 490b CRT Rejuvenator, and I have tested it on a worn tube. It works, but it is much more invasive than this mod as it super heats the cathodes, burning away the dead layer on the cathode tips and liquifying new barium so that it flows to the cathode tips. If you aren't lucky, the super heating does more damage.


If anyone's interested in seeing this, check out this German video of an old TV technician showing the rejuvination of a CRT. Starting at ~10 minutes for a B/W tube and ~16 minutes for a color tube.

https://www.youtube.com/watch?v=MUGOzG6MEZQ


I have found that placing the front glass of the CRT face down, while using a rejuvenator yields better results more often. My theory for why this is true is because the rejuvenator super heats the cathodes. This super heating burns away the dead layer at the tip of the cathode, AND it also slightly liquifies the barium. If the CRT is face down, gravity helps the dead layer flake off, away from the electron gun and it helps the liquified barium make its way to the center tip of the cathode. This theory would suggest that rejuvenating a CRT while it is in a centrifuge, would yield even better results, as the centrifugal force could be very high, helping pull fresh barium to a sharp center tip of the cathodes.

10 years from now, CRT life extension techniques will become increasingly popular, as gamers realize the number of hours left in their precious CRTs are running out. Using this mod in addition to a CRT rejuvenator, and using over-volting of the CRT's heater will allow for squeezing every last bit of juice out of the last remaining CRTs on earth.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Thu Feb 18, 2021 7:41 pm 


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lol you'd need a hell of a large centrifuge to spin a 27" tube + some kind of slip-ring electricial connector to power the rejuvenator as it spins! If you ever set that up, you absolutely MUST make a video of it, lol. :mrgreen:


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Thu Feb 18, 2021 7:55 pm 



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Posts: 63
Don't use rejuvenators on Trinitron tubes though. The cathode of these tubes are smaller and known to just burn away when using a rejuvenator on it.

I had a PVM-14M4 with a bad tube. I got a replacement tube for it but I thought I might experiment with my rejuvenator on it. It burned away the cathode and only one colour is working now.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Thu Feb 18, 2021 9:40 pm 


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ElBartoME wrote:
Don't use rejuvenators on Trinitron tubes though. The cathode of these tubes are smaller and known to just burn away when using a rejuvenator on it.

I had a PVM-14M4 with a bad tube. I got a replacement tube for it but I thought I might experiment with my rejuvenator on it. It burned away the cathode and only one colour is working now.


Trinitron tubes are known to be more sensitive, yep. Later rejuvenators like the CR-7000 tend to work a lot better with them, as they have better = gentler settings for it.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Thu Feb 18, 2021 9:51 pm 


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LukeEvansSimon wrote:
I have found that placing the front glass of the CRT face down, while using a rejuvenator yields better results more often. My theory for why this is true is because the rejuvenator super heats the cathodes. This super heating burns away the dead layer at the tip of the cathode, AND it also slightly liquifies the barium. If the CRT is face down, gravity helps the dead layer flake off, away from the electron gun and it helps the liquified barium make its way to the center tip of the cathode.


Is there a risk of debris falling into the shadow mask with this method?


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Thu Feb 18, 2021 11:14 pm 


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Excellent work. Sorry to drag up an issue from a few pages ago - but since you've got the Geiger counter, did you take any readings from the sides / behind the tube? That is something I've always been interested in because the shielded glass (blocking X-Rays) is thickest at the front, while the cabinets of most of these TVs will be plastic.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Fri Feb 19, 2021 3:26 am 



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Ed Oscuro wrote:
Excellent work. Sorry to drag up an issue from a few pages ago - but since you've got the Geiger counter, did you take any readings from the sides / behind the tube? That is something I've always been interested in because the shielded glass (blocking X-Rays) is thickest at the front, while the cabinets of most of these TVs will be plastic.


I used my Geiger counter to measure x-rays from all sides. No x-rays were detected with or without the mod. The x-ray theory would suggest that the x-rays produced by a CRT are lower energy than the max anode voltage used on the CRT. The high voltage anode cap on a CRT is under 30kV, so the x-rays cannot have an energy above 30keV (this is the first law of thermodynamics). At this low energy level, the x-rays are not capable of passing through the glass of the CRT.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Fri Feb 19, 2021 6:45 pm 


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Cool, thanks again!


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Sun Feb 21, 2021 8:27 pm 



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Alright so I finally had time to do the TVL test. I hooked up my PC with CRT Emudriver to the E3431D I modded. I first measured the cathode voltage of one of the colours.


And holy moly the output of the RGB amplifiers are I think one of the most limiting factors.

You will see a series of oscillograms. Each one has an upper and lower line. The upper line represents the voltage for black and the lower for white. I put on alternating black and white lines.

Image
256 lines

Image
384 lines

Image
512 lines

Image
1024 lines

You can see the that the amplifier is just not able to follow the signal after about 384 lines. It should be a nice square wave anyway but what we get here is sinusoidal.

Then I put on the TVL card and compared them with and without the mod. As I already expected after having measured the output of the amplifier there is no change to be seen in the TVL before and after the mod.

Image
Click here for high resolution: https://www.dropbox.com/s/ewpjfj2pesrgp7n/TVL_Test.png?dl=0

So I think in order to see any noticeable difference we need to also upgrade the amplifiers on standard consumer television. I have a BVM-D20F1 and I will put on the same test setup there and measure the output of the amplifier. I suspect that they have a much higher bandwidth.

------------------
Regarding the load on the flyback due to the added winding for the mod. I measured the current consumption by measuring over the 330 Ohm series resistance I put in line with G1 and as I expected the consumption is negligible.

Image

You can see peaks for 175mV which equals to aroung 500µA. At 120V that equals to around 50mW. But also you can see negative peaks so the mean current provided by the winding is almost zero anyway. All that peak current is provided by the capacitor. So there isn't any meaningful additional load on the flyback.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Tue Feb 23, 2021 5:15 am 



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ElBartoME wrote:
...


The square waves rounding into sine waves, as well as decreasing in amplitude is exactly what you'd expect to see in an analog amplifier that is being fed an input signal that is too high frequency for its specified bandwidth.

As I mentioned before, my latest CRT project is a custom neckboard that has very high bandwidth cathode amplifiers, as well as a pulse transformer and potentiometer for creating a negative voltage rail for an adjustable G1 voltage, as opposed to having to add a winding to the flyback's exposed core. Pulse transformers are inexpensive and it will make installing the mod easy for lazy people.

I don't care about the naysayers. Nobody is making new CRTs anymore, as creating the tubes requires specialized manufacturing tools that no longer exist in factories. HOWEVER, getting a new custom CRT neckboard developed is easy given the on-demand printed circuit board companies in every major country. So I am committed to seeing how far this TVL boosting mod can be refined. I need to carve out time to finish prototyping and testing the custom neckboard. I am now leaning towards using the 2SC3782 NPN transistor in a cascode amplifier circuit design, since the 2SC3782 is sufficiently high voltage and high bandwidth, still manufactured, inexpensive, and is available from popular retailers.

I am wondering if the super neckboard should also have a voltage multiplier for the G2 anode, to work around the limited screen voltage that, apparently, some flybacks output.


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 Post subject: Re: Mod a CRT to increase its TVL
PostPosted: Tue Feb 23, 2021 9:21 am 



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Posts: 63
ElBartoME wrote:
I am now leaning towards using the 2SC3782 NPN transistor


The 2SC3782 looks very interesting, but you linked the KSC3503DS instead?

ElBartoME wrote:
since the 2SC3782 is sufficiently high voltage and high bandwidth


The bandwidth is very impressive but it seems the breakdown voltage is 200V. The transistors used in my E3431D have a breakdown voltage of 300V. I haven't measured any voltage near that but I assume there must be a reason why they chose that number. I assume it depends on G2. If I crank up G2 the voltage to achieve black levels change too. So I guess in my operation point I have at the moment I don't need that high voltage to achieve black. But still I would feel better if the breakdown voltage of a new transistor is the same. Do you have any suggestion?

LukeEvansSimon wrote:
I am wondering if the super neckboard should also have a voltage multiplier for the G2 anode, to work around the limited screen voltage that, apparently, some flybacks output.


By the time G2 reaches the neckboard it's already DC. Making a voltage doubler would be difficult.


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