Sony's PVM TVL count - Same pitch and size but more TVLs?

[tongshadow]

I'll get right to the point, why are some tubes rated at higher TVL even if the screen size and AG Pitch are the same? What's the other factor involved in resolving a higher count of vertical lines?
According to this site the PVM-14N2U is rated at 500 TVL and a AG Pitch of 0.25mm:
https://www.bcs.tv/store/model_detail.cfm?id=13812
However, the PVM-14M4U rated at 800 TVL also has an AG Pitch of 0.25mm:
https://www.bcs.tv/store/prod_detail.cfm?eq_id=437707

Is the site wrong? I've seen discussions here about this before, but it was comparing 800TVL and 900TVL tubes. The difference was just in the "grade" of the tube, but the part numbers were the same and the difference is marginal. But those who own both 500 and 800 TVL tubes know the difference is noticeable as you can see in this picture:
https://i.imgur.com/wDEfK6U.jpeg

So whats the other variable involved in a higher TVL count here if the AG pitch and screen size are the same?

[oldgamer]

I would guess it's the quality of the electronics, that is, how capable the chassis is.

I don't remember the exact model now, but there is one model that uses the exact same tube as the 20L5(800 TVL) but is only 600TVL.

It's probably the thickness of the electron beam, aka spot size. The better chassis have it thinner, and also maybe components that properly allow higher video bandwidth.

[tongshadow]

One thing I noticed on the N series (might be the same for other models) is that the TVL is stated to be "at the center", so at the corners it loses TVL count. Is this loss caused by the electronics or the manufacturing process? Maybe it's hard to make the 0.25mm stay consistent from corner to corner and they select the tubes for the higher spec monitors...

[Dochartaigh]

According to this site the PVM-14N2U is rated at 500 TVL and a AG Pitch of 0.25mm:
https://www.bcs.tv/store/model_detail.cfm?id=13812

Going off memory here, but I'm pretty sure Sony never listed the AG pitch of that N monitor. I didn't see it in their brochure, manual, or service manual I just skimmed through either...

[matt]

As discussed in the lengthly "mod a TV for increased TVL" thread, it's also determined by beam spot size and the bandwidth of the RGB amps. For a lot of monitors these are more important than the pitch of the grille itself. That would explain why different grades of 14" monitor all use the same tube.

[tongshadow]

The funny thing is that the AG pitch is vastly different on the 8 inchers
https://i.imgur.com/zdDQmeg.jpeg

I dont think a tighter spot would accomplish a big improvement in this case.

[LukeEvansSimon]

As discussed in the lengthly "mod a TV for increased TVL" thread, it's also determined by beam spot size and the bandwidth of the RGB amps. For a lot of monitors these are more important than the pitch of the grille itself. That would explain why different grades of 14" monitor all use the same tube.

Whenever someone says “spot size”, I appear. Here is the thread that Matt mentioned. TVL is determined by spot size, dot pitch, and signal bandwidth. When using s-video or better, signal bandwidth is bottlenecked by the amplifiers that drive the CRT cathodes. These amplifiers have to swing a cathode’s voltage by 100 volts peak to peak. Doing that fast is challenging for an amplifier.