[Alex KL-1]

Fortunately I had some free noise time to play with it this weekend.
My notebook indeed have the NTSC-J.
So, I proceed with the tests. With interesting results...

I'm able to test with 2 B&W TV's, one small 7" with transistor video amplifier. I employed DC restoration is similar to one used in the System A Modulator in the The Valve Pages (Tr4, fig1: emitter clamps the base signal of the video amp), and collector is DC coupled the video out to the cathode CRT.
These are already pretty good even with PAL-M and NTSC. High quality clamping. With NTSC-J, it basically moved the DC level as predicted, and bright needed to be readjusted. No statiscally important difference in black level stability. Only a little impression that the NTSC-J can be more impervious to extreme scene changes, but then I'm relying on my eyes only...

Then I tested with a Admiral that I applied DC restoring at the g1 of the video out tube, using a Ge diode, and DC coupled the anode to the CRT. Again, no statiscally difference for the black level performance per se (only the adjustment is necessary), but in these, I swear that the PAL-M have better less black crushing, ie low level is slight easier to see. I not noticed it with the small TV one, and seems to be just the opposite... Again, could be the difficult to adjust, or my eyes, or the notebook video amp indeed having a slight difference in gamma, and certainly the 2 TV's also have some difference in CRT curve response, basically.