Low-Bandwidth CRT - why?

Denton, Adam (Exchange)

I have a 564B which has a stated mainframe bandwidth of only 10MHz --
a remarkably low figure IMO. Can anyone here tell me what aspects of
physics can limit the bandwidth of the CRT? In this unit the
vertical and horiz defl plates are driven *directly* from the plug-
ins, so I (being naive?) would guess that, if I could produce a plug-
in that could deliver the required 160Vp-p at, say, 400MHz, into the
capacitance of the vertical plates, that I should expect to be able
to view 400MHz on that CRT (assuming I drove the horizontal
accordingly, which BTW is also driven directly from the [right side]
plugin). The distance from plug-in to CRT is about 6 inches, fed
thru 2 pairs of thin wires each about an inch apart, so I would not
expect any transmission-line effects (well maybe at 400MHz but, say,
50MHz should be fine).

It's an electron beam, so if the plates have potential, it's gotta
deflect, yes?

(of course it's rather difficult to deliver 160Vp-p at 400MHz but
that's another story....)

Or is it just Tek marketing... :-/


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