Re: 2465B CRT board values

Chuck Harris <cfharris@...>

Hi Hirofumi,

Scopes, like the 2465B, have only a single electron beam to
draw all that is on the CRT screen. They do this by time
multiplexing the beam between the readout, and the traces.

If the CRT only displayed a single intensity, and hence a
single electron beam current, it would be easy to just set
a single voltage on the focus lens, and get best focus on the
screen. But they don't.

So, tektronix made a special non-linear circuit that took as
its inputs horizontal sweep rate, beam current, and focus control
voltage, and used it to warp the voltage driving the focus lens
into a pretty good compromise between high intensity and low
intensity trace focus... but still a compromise...

And, since a sharp bright main trace is the money maker for a
scope, it gets money spent on its own adjustment for high
brightness sharpness, and the readout focus gets compromised.

If you do the CRT adjustments in the CAL section, you too can
have a chance to decide on how to do that compromise. Pay
particular attention to "HIGH DRIVE FOCUS".

The CRT adjustments section of the calibration can be done on
its own, and only needs a 50KHz sine wave.

-Chuck Harris

Hirofumi Momose wrote:

Hello Chuck, Jon

Chuck wrote:
I haven't found a 2465B that has its best focus at 12:00
Oh.. My unit is just 'normal'. Understand.

Jon wrote:
"If it ain't broke don't fix it"
"leave well enough alone"
Now works. Best focus point of trace/readout is a bit different.
But no problem to read.
Yes ,no more tune and leave it.

Thank you.
Hirofumi JJ2PNX

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