Re: Update on 2465

Siggi
 

Hey Chuck,

thanks for the correction - can you share where you come by this
information?
Naively I looked at the HV and CRT circuits, and took the -900V line from
the HV supply towards the front of the CRT neck to go to an expansion mesh.
Hmmm, maybe just a case of RTFM :). The -900 is termed "slot lens voltage"
in the Cathode Supply section of the Theory of Operation.

Incidentally find that there's no contest between the spot size and trace
clarity between my 2465 and my 485, the 485 has a much clearer trace. At
one point I routed the X/Y/Z from my HP8566B's display unit to a scope for
diagnostics of the display unit, and the 485 was the only scope I own that
was able to resolve the detail. See <https://goo.gl/photos/21ASGFDsU2Zd9qA66>
I believe that display is 1024x1024.
Maybe this is just a sign that my 2465 needs some TLC, though after I got
the 2467 she'd be better with someone who'd use her more, probably :).
The dot size on my 2467 is quite absurd in comparison to either of those -
though it wins hands down on brightness (which is the MCP trade-off).

Siggi

On Thu, 5 Jan 2017 at 10:14 Chuck Harris cfharris@... [TekScopes] <
TekScopes@...> wrote:



A minor nit: The 2465 family CRT does *not* have an
expansion mesh lens!

It uses a "box" lens based on a quadrapole design.

The quadrapole lens eliminates most of the distortion
and all of the flaring exhibited by the expansion mesh,
to the point where the beam size after expansion is almost
exactly the same as it would be with a longer CRT that
has no lens.

The 2465 family has a much shorter (2 inches) CRT with
a much larger (36% more area) screen than does the 454A.

If you could expand the 454A's screen the 36% from
8cm x 6.4ch to the 2465's 10cm x 8cm, the 454's dot
would be much larger than the 2465's.

The reason most people think the 2465 has a larger,
fuzzier beam, is because the beam incorporates all of
the extra noise due to its 400MHz deflection amplifier
bandwidth.

Reduce the bandwidth to 20MHz, and the beam size is
very compact.

-Chuck Harris

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