Re: Update on 2465

Chuck Harris
 

That the 2465 has a quadrapole lens comes from a combination
of observation... I have a busted CRT... and reading about it
in one of the tek magazines.

When you look at your 485, do notice that the CRT's screen is
the same size as the 454A's, 36% smaller than the 2465.

That 36% is very significant in terms of spot size.

The 485, doesn't have any lens for increasing the deflection
sensitivity, so, that too helps the impression of size.

Another factor that makes the 2465 look fuzzy is all of the
switching that is going on to handle the display readout.
That switching causes a tiny, almost imperceptible tail on
the trace every time the beam flits away from the trace to
draw part of the readout. The trace looks better with the
readout off.

Try comparing your 2465 at 20MHz BWL, with the 485 at 20MHz
BWL. Take a measurement of the beam diameter at the same
intensity, and compare it to the 2465. In my experience,
the 2465's is about a third larger.

-Chuck Harris

Sigurður Ásgeirsson siggi@... [TekScopes] wrote:

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

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