AVR-Chat

Arir -

Here is some more information about CRTs. 

Magnetic susceptability (interferance) is very common with
CRT. Most manufacturers put a metal magnetic shield over
the tube. Often, it is a special metal (one has a trade
mark of "mu-metal", I believe). With home TVs, the color
ones are more critical for external magnetic fields. There
is usually a "degaussing" circuit that demagnetizes the CRT
every time it goes on or off. 

There is a big trade-off between accelerating voltage and
many other things. The spot becomes brighter with higher
voltage. But the beam becomes more "stiff". This means that
it takes a higher deflection voltage (if it is electostatic
deflection).  It is common practice to run the deflection
plates near ground to make connection to circuitry easier.
This means two supplies, however, one for the cathode and
one for the screen. It is common to use high-frequency
oscillators for the high voltage (that is, switching power
in modern terms). Because the voltage is quite high
(5-10Kv), the transformers tend to be difficult to make. 

All of these factors (and many more, including weight and
size) have contributed to the modern trend of using LCD for
oscilloscope displays. 

Jim
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