465 Scan Expansion Mesh
I believe you're right, Stan. I'd heard both explanations.
Actually, the geometry story doesn't pan out well if you've ever seen
one of the guns outside of the jug. the mesh is hemispherical in
shape. If it dealt with geometry, I'd expect an odd shape to
compensate for the extremes of the rectangular screen. For those who
have never seen one, it is interesting. Very, very delicate, and so
fine that when you hold it up to the light, it's like a diffraction
grating, splitting the light up into different colors. It's also so
fine that it will hold water. One little puff of air and you dimple
it permanently. I send a piece of a mesh to friend Dale Johnson
(used to work for Tek in the Dallas Service center, but at the time
was working for a company that serviced scanning electron
microscopes. He put the piece of mesh under a scope and the view was
really interesting. It's quiet obvious that it's etched and not a
woven screen that one first envisions. I don't know whatever
happened to the Polaroid of that scan that I had. It should would
make for an interesting post, but that was 25 years ago!
Sometimes, during manufacturing, a little dirt gets inside the jug
and finds its way to the mesh. The resulting display is a small spot
on the CRT that just can't be illuminated by the beam because of the
shadow effect it creates. I was rather irritated one time when a new
465B came in with that exact problem and the factory wasn't going to
honor a warranty replacement of the jug because it was "still within
all specifications of CRT anomolies". I put myself in the customer's
shoes and decided that I wouldn't put up with a something like that
in the windshield of a new car. Why should the customer put up with
a manufacturing defectlike that in his $3500 scope? We replaced the
CRT anyway and shoved the old one down factory's throat. Tek was
starting to change from a very customer-oriented organization to a
very money-conscious outfit.
And Stan, I don't know that I agree 100% about the mesh being a bad
deal compared to what the 535 had. I've never seen a burned CRT in a
scope with a mesh and you can't say that about the old ones. The
mesh diffused the beam enough that the CRT was pretty burn
resistant. To me, the ±1 digit bobble of a digital scope is far
worse to look at than the fuzzy trace of a 465.
Stan or Patricia Griffiths <w7ni@...>
And Stan, I don't know that I agree 100% about the mesh being a badHi Dean,
It is great to hear other opinions and views on this sort of thing especially
from someone who was as close to the situation as you have been.
I suspect the difference in burned phosphors was due to the change from P2 to
P31 for a standard phosphor in most general purpose scopes. Both of those
phosphors look very much alike to the eye, being blue-green in color. I
think that phoshor change took place about 1965 or so. Scopes shipped before
that time with P2 phosphors where MUCH easier to burn . . . I don't think I
have ever seen a CRT with a mesh and P2 at the same time . . .
Yes, I put some of that mesh under a regular optical microscope here and
found the same thing you did . . . it is etched rather than woven. I was
surprised to discover that . . .
Whether the fuzzy trace was a bad tradeoff or not is another one of those
opinion issues. I just talked to one guy who told me he could see stuff
(tiny wrinkles) in the trace of a 454 that just are not there in the display
of the same signal on a 475, even though the 475 has 50 MHz more bandwidth
and a much larger screen. The position I am coming from is that I was a
Sales Engineer for Tek at the time mesh CRT's were introduced and I can tell
you that MANY customers noticed the difference and were not pleased . . .
they always expected the new model to be better, in every respect, than the
one it replaced, sort of like cars. Well, they aren't always better in
performance. Sometimes they are better in price, instead. Sort of like cars
. . .
Yeah, try to get most people to agree that the addition of the engine
computer on a car was a step forward. I think the step forward was
the fact that I have yet to not have a computerized car start within
2-3 seconds whether the temperature was -10°F or +110°F. The step
backward is how, with so many vehicles being produced that (1)
manufacturers over the world haven't settled on a common computer
platform and (2) that to replace one costs as much as my full-blown
home computer. I think the latter is simply because the
manufacturers have us poor consumers by the kahoonies and know it.
And back to the mesh vs. other methods. Not only can one compare
meshless CRTs from the 1960's to the 465/475 and now to the digital
scopes, but look at the digital scope displays. They're going to be
limited not only because of the ±1 digit bobble, but because of the
finite resolution of an LCD or a tri-color CRT dot pitch. No point
in using ADCs with resolution better than the display resolution
unless you have a method of "magnifying" the vertical and/or
horizontal to take advantage of the increase ADC resolution. I've
not looked up the LCD and color CRT specs to see where the two
resolutions converge. Might be interesting! It's an issue not
unlike having a 4-1/2 digit DMM display and only 0.5% accuracy on DCV
and 1% accuracy on ACV.
By the way, I had forgotten about the phosphor change. The P31 is
more durable, that's for sure. I have seen a few P11's that were
wrecked on 7904's and 485's that were being used for nuclear research
out in Amarillo. They were always set up with a camera (obviously,
with a P11) waiting for a single-shot event with the intensities
cranked up to max. They were a BIG market for the 7104 in the OKC
And regarding nuclear research, I remember a field engineer telling
me about selling a lot of transient digitizers to the nuclear
research community. They'd put a TD down a hole with a bomb with the
cabling leading to the blockhouse a couple of miles away. They'd
blow up the bomb and the TD would send the signal out of all the
stuff they were monitoring -- about 1µs before it went into total
meltdown -- and then in the blockhouse monitoring station, they'd
wait for the signal to show up and then after it was captured, high-
speed clamps shut the lines down so the the massive EMP that was
right on the tail of the data didn't totally destroy all the
monitoring equipment. But the poor transient digitizers .... they
got to make one and only one measurement in their entire lives before
that serial number ceased to exist. Danged expensive probe!
John Rehwinkel <spam@...>
Yes, I put some of that mesh under a regular optical microscope hereI have a friend who has an electron microscope -- if anyone cares to
lend me a bit of mesh, I'd be glad to get pictures of it and post
them. Naturally, I'd return the mesh too if you like.
-- John Rehwinkel KG4L
Stan or Patricia Griffiths <w7ni@...>
And regarding nuclear research, I remember a field engineer tellingYes, I think a lot of 519 scopes suffered a similar nuclear fate. In those
cases, they used polaroid cameras on them and the scopes and cameras were not
exactly melted down . . . just radiated so intensely that they were too "hot"
for anyone to use. As I understand it, some guy in a protective suit would
go rescue the exposed film and they would bury the scopes and cameras. Those
were "one-shot" deals, too. There are some pretty pristine 519's in a vault
somewhere . . .