What EXACTLY determines CRT Line Count (TVL)?

[DatPhosphorGlow]

Marketing BS aside.

I have a BVM-20E1U with a good tube. I also have access to a PVM-20L5 with an exciting brand new tube. The famed BVM-20F1U has a different tube part number than my BVM-20E1U, as does the PVM-20L5, according to Sony service manuals.

I've heard of people swapping tubes between these three models (including the 800TVL PVM-20M4U). Why did Sony give them different part numbers? Are they just the same part numbered tubes binned for each tier of BVM/PVM?

My flagaship BVM-20E1U is advertised as 1000 TVL.

The famed BVM-20F1U is advertised as 900 TVL.

The PVM-20L5 is advertised as 800 TVL.

Am I going to lose my fancy 1000 TVL line count if I put the 20L5 tube in my 20E1U?

Do they have different "resolutioned" aperture grills in their tubes?

Or is it the circuitry and yoke that are able to control the beam pattern more tightly that allow for the higher TVL count?

[fernan1234]

Recently there was some discussion that addresses all your questions. Find it here: viewtopic.php?f=6&t=69510

[DatPhosphorGlow]

Thank you fernan1234. Quickly skimmed the thread, will read in detail later today. But now that I see it again, I remember reading about the aperture grill pitch difference between the 900 and 1000 TVL monitors in the owner's manual before. That clarifies that the 20F1U and 20F1E definately have a different tube.

I hypothesized before discovering that info back then that the aperture grills have to be different to have a higher line count. But that's probably only part of the equation when it comes to TVL, I think. Still need to figure out the all the details of variables that contribute to TVL count.

[fernan1234]

To answer your question more generally, what determines CRT line count is the ability of the tube to pass a certain threshold in a TVL/resolution test pattern.

Logically we can assume that manufacturers would produce grilles or masks targeting a certain pitch as a minimum, which among other factors would translate to the ability to resolve certain level of detail (as measured with the number of vertical lines that can be seen clearly in a test pattern). That's why in promo material you often see that tubes can resolve "at least X TV lines".

What I have always thought is that this manufacturing process was never 100% exact, which meant that during quality control all tubes would be tested to pass the minimum targeted, perhaps finding a few that would not pass and thus would be binned (or if just below spec maybe put into B-stock units?), while those that exceeded the target number would go into lucky units, or as in the case of Sony specifically labeled tubes and units marketed as extra high grade. Perhaps Sony discovered that they were getting enough tubes that targeted at least 900TVL were doing over 1000 and came up with the 20E1 line (and tubes targetting 800TVL doing over 900 for the 14E5/14E1 monitors). However, some people believe that Sony specifically had two different production lines for each of the grade tubes of the same size. If my conjecture is correct, it would mean, for example, that there may be a few D20 and A20 monitors that could actually resolve up to 1000 TVL.

The general consensus though is that at this point, and especially with all of these tubes getting older over time, you would find it very hard to say the least to be able to tell any difference between same-size models marketed as 900 vs 1000 TVL, assuming both are in similar condition.

One final thing to note is that TV line specs often assumed the highest quality connections (SDI or RGB), since a composite or S-video input in the same monitor would be less resolving. Some promo material indicates TVL count for both SDI/component and "NTSC" (i.e. cvbs or y/c).

[tongshadow]

Do they have different "resolutioned" aperture grills in their tubes?

Yes, according to the service manual the E1U has a 0.22mm stripe pitch.

Or is it the circuitry and yoke that are able to control the beam pattern more tightly that allow for the higher TVL count?

Also, yes, in some cases like the M2U and M4U. The latter has double focus and this difference is large enough to make a swap impossible afaik.

And dont always trust service manuals, specially concerning part numbers as there can be errors.

[Ed Oscuro]

TVL is simple. Feed the screen a test pattern of vertical line bars. Take the height of the screen - which is a ratio of 3 units wide to the screen's 4 units height. Find the middle of the screen with a dimension equal to its height (i.e., the middle 3/4 of the screen). Count how many vertical pairs of alternating black and white lines can be individually discerned across that middle 3/4th of the screen without blending together into a low-contrast gray mess. A higher TVL count here indicates a more tightly focused beam, which also means that each line will be narrower in both dimensions, both horizontally and vertically. That should explain why TVL can be much, much higher than 480 lines of resolution even on a 480i or 480p monitor - it's measuring potential resolution horizontally, not vertically.

This is similar to the old line pairs per millimeter (lp/mm) measurement for optical lenses. These are good enough measures for the analog world and are easy to understand, but they're not useful in modern contexts outside the lens world because they don't take into account the subtleties of noise performance in sensors, or light transfer at different frequencies. For those cases you want more modern measurements like MTF (lenses) or SFR (lens + sensor combinations). And of course, flat panel display resolution in static scenes can be measured precisely without running the TVL pattern, as each pixel is more or less physically separate from its neighbors.

I thought Sony was quite good about updating their service manuals, and I know you can find various dated manuals for some sets out there in the wild. I assume the more recent ones are more reliable, if there is a question about part numbers.