Re: 7904 excessive shadow/flare
The dome mesh is an anode, though it is called a "Slot Lens", ontoggle quoted messageShow quoted text
the schematic. It is at pin 4 on the CRT.
I don't know if "Slot Lens" is the more formal name, or if perhaps
it isn't a dome?
The traditional dome mesh lens, as I have seen them is a super fine
stainless steel window screen with a pronounced bow in the screen
direction. Maybe the 7904 is using a special lens that only magnifies
the Y direction, and not the X direction, using slots instead of holes,
like the mesh lens?
I haven't broken a 7904 CRT as yet, so I haven't seen the lens.
They use two quad pole lenses to focus the beam before and after
the vertical plates.
I looked at my 7904 and 7854 more closely, and the 7904 is adjusted
to have a much hotter beam, just about always, than the 7854. The
way I can tell, is the beam spot, although P31 phosphor, is always
a lot bluer than the 7854, which is simply a boring green spot on a
The 7854 is also 100MHz lower bandwidth than the screaming 500MHz
7904. It is different, even though it uses the same CRT.
And, (there is always an and with me...) the 7854 is 10 years newer
than the 7904. Surely there were some CRT improvements in that time?
On Thu, May 23, 2019 at 02:42 PM, Chuck Harris wrote:O.K. indeed the artifact is two times more pronounced with my 7904 with respect to my 7854 (grossly speaking).