[Alex KL-1]

I have almost the same question...

But is a doubt, also... since I worked at a time with only in-line CRT, I dunno if have differences to a delta-gun tube: I have one delta-gun in collection (that one I yet have to correct some purity issue), but it have excellent image only after 2 or 3 minutes; it starts blurry. And, it have a maximum contrast it can show: If I try to crank it to have a more luminous image, it blurs a lot.
To be fair, it's brightness is good for night watching...

About this contrast limit, is that manner in delta tubes, or mine is showing it's age?

I like this CRT, it render the colors very rich; outstanding!

Another doubt (a curiosity/musing) now, if people don't mind: all delta-gun CRT are absent of the black matrix, or some use it? This CRT have very low light leakage between adjacent "pixels", like modern good CRT. The focused image is second to none... (after it warms)
Or, in another words, if the black matrix concept are apllied only to in-line CRT?