AVR-Chat

Thank you Mike and Jim, 
I am driving the crt in XY  mode I don't use any raster actually I used
a previously available schematics for the tube,   the power supply may
have problems as you stated, I previously inspected those signals and,
tube is driven with 1400 volts anode-cathode voltage, however there is
about 20 volt ripple on it because it uses typical diode -capacitor
voltage doubler circuit stages to obtain 1400 V from a 170 AC winding of
the transformer. Other parts of the circuit also use 7815 Voltage regs.
Etc. and their output seems very clean when inspected on the scope, , X
and Y deflection amplifiers have transistor stages, and they produce
very stable x and y signals  ie. Horizontal, vertical, 
When I inspect the tube datasheet I see different anode terminals like
A1 A2 A3 , and single cathode terminal, 

By the way, I showed special care to ground loops in the board and still
there may be problems you may be right, also routed its signals with at
least 36 mils width, and 72 mils for ground signals. 
I am now inspecting the board but not very sure if it is going to help, 

Do you think tube pyhsics are so intolerant to 20 V ripples on the
anode voltage?  The flickers when signal is moved upwards are due to
it?, I will   put a high voltage capacitor there...







-----Original Message-----
From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On
Behalf Of Jim Wagner
Sent: Tuesday, December 06, 2005 9:08 PM
To: AVR-Chat@yahoogroups.com
Subject: Re: [AVR-Chat] Driving Oscilloscope CRT like Memory Mapped
Graphic Display


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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