DIYbanter - View Single Post - CRT question, partly curiousity, engineering wise

Jim Yanik

(Samuel M. Goldwasser) wrote in
:

Robert Macy writes:

On May 1, 5:25*am, Robert Macy wrote:
On May 1, 2:47*am, Jeff Urban wrote:

...snip...
Why the hell didn't they just go with electrostatic deflection
like in a scope ?

Think about it, you people out there who know engineering, think
about it. Why not ? I understand about the CRT parameters and the
variance with beam current and I also know about beam density. I
know these are all problems, but using magnetic deflection solved
none of them !

THINK THINK about that.

...snip....

Magnetic deflection can bend the beam at a sharper angle than the
electrostatic deflection.

Look inside an old Tektronix scope, which uses electrostatic
deflection. That neck is LONG because the angle of deflection for
physically realizable voltages is so small.

and with a long neck and electrostatic deflection,the CRT was amazingly
sensitive to Earth's magnetic field,thus requiring shielding.
Telequipment scopes were infamous for their poor trace rotation
calibration,they would never hold the setting.Move the scope,and you had to
readjust the TR.

Forgot to mention the obvious:
The required Electrostatic deflection voltage goes UP as the HV goes
up, because the electron spends less time in the gradient between the
plates

it depends on the electron gun structure.
the TEK 2465 tube had specially constructed deflection plates and a
focusing "lens" instead of the mesh lens typically used. It was designed to
use low deflection voltages that could be provided by hybrid ICs instead of
discrete defl.amps with HV transistors. the 2465 tube was fairly short,too.
I used to have a booklet that described the CRT tech for the 2465 tube,lost
it when the Orlando Service center was shut down.

Alas,all that technology is gone now.TEK no longer makes it's own CRTs.

Anybody out there confirm the following statement?
In contrast, the required Magnetic deflection goes DOWN as the HV
goes up because the electron is moving faster through the field and
gets 'bent' more.

Nope.

I fail to see how a "faster" E-beam will bend more under magnetic
fields,but not under electrostatic fields.

--
Jim Yanik
jyanik
at
localnet
dot com