Could not load tags. Latest commit. Git stats 14 commits. Failed to load latest commit information. View code. The circuit can source several milliamps so be extremely cautious while using it to prevent nasty electric shocks. Would this deflection-board be suitable to convert a 37cm about 15 inch TV to a XY monitor?
The old HV and everything on the TV is intact. No, Those picture tubes use magnetic diflection with coils wrapped around the neck of the tube, this circuit looks like its designed for electrostatic tubes that have plates built into the neck instead. The old Asteroids game used a monitor that is very similar to a TV. The monitor was more or less a TV with lots of parts missing. Converting a TV would require rewinding of the vertical deflection yoke and co-responding changes to the drive circuitry.
It is NOT a simple conversion as I previously thought. CRT hacks are not about presenting information. They are about putting on display something functional and elegant. Yes, junior, we all have smartphones and I could use mine as an alarm clock if I needed to.
Electrostatic deflection is build into the tube CRT. All is not lost, there are plenty of old oscilloscopes around and sometimes you even find just the tube on offer.
Very early sets, from the 30s often had dinky electrostatic CRTs. You may choose to use a smaller lower voltage or larger higher power transformer depending on the CRT you are using. Keep in mind that the display size is inversely proportional to the DC voltages so lower voltages can still achieve a large display, but the CRT display will be more sensitive to the Earth's magnetic fields and orientation.
If the Hammond X transformer is used with a smaller CRT then you may need to remove one stage of the negative voltage doubler replace C16 with a wire and do not populate diode D4 to reduce the maximum negative voltage rail to around V. Complete parts list and schematic: OscilloscopeCrtDriverData. Bill of materials CSV file to import into Digikey cart: scopedriver.
If both plates are at zero volts, the beam passes between them uneffected. When one plate is driven more positive than the other, the beam will be attracted to the more postively charged plate and repelled by the negative plate.
The deflection plates, and other elements within the tube, operate at and require very high driving voltages. Thousands of volts in many cases. The function of Eric's boards is to convert low voltage drive from Tiny TV to the extremely high voltages required by these cathode ray tubes. It also creates two scanning ramp voltages, in sync with the video, for horizontal and vertical scanning.
These are also sent to PCB2 via J3. Horizontal, vertical and video drive are known as X, Y and Z signals when discussing graphic or oscilloscope displays. This board runs on four power supplies. They are; 6. A generous array of potenetiometers allows for very flexible set up so that it can support the greatest number of CRTs.
Voltage is set with potentiometer. Work around this board with great care. Here we see my plus and minus 3, volt bench power supply. This is a conductive coating on the inside of the CRT between the deflection plates and the screen phosphor. This way, low velocity electrons pass between the deflection plates and are deflected more than fast electrons.
After passing the plates, the electrons are now influenced by the PDA electrode and accellerated to the phosphor. This gives high deflection gain along with higher brightness than a tube lacking this feature. So, here we go. Fired up the boards. No smoke. Tweaked the pots until I got the best image possible. Dead as a door nail! No scope, no more troubleshooting this weekend. Looking at the pictures above, there is an obvious problem with the horizontal scan on the left side.
Before the scope died, I was able to prove to myself that the Tiny TV board was putting out three good signals at about 3 volts amplitude. I probably missed an update somewhere on Eric's page. Will investigate that next time I sit down to the project. Obviously, this is now on hold.
Let's discuss P7 radar phosphor. P7 is a two stage phosphor. The electron beam does not have a strong effect on the yellow phosphor. The yellow phosphor is, instead, excited brightly by ultraviolet light. The yellow phosphor's second desirable property is that it glows for a usable period time after stimulus is removed.
Up to 30 seconds in a darkened room. This long persistance was used effectively as an image storage memory in the earliest days of analog radar and before computer memory was plentiful and cheap. If one wishes to view the long persistance effect of P7, a yellow filter can be placed over the tube to block the blue light. Conversely, if one wishes to view, and perhaps photograph, the blue phosphor, a blue filter is used.
The scale above represents the relationship between the color difference signals in composite video. The vertical axis is R-Y and the horizontal axis is B-Y. I chose this example as it shows the primary colors and their inverse evil twins.
Additive and subtractive primary colors. Note the color boxes on the vectorscope display above. The opposite color of blue is yellow. In the case of a black and white video signal, the vectorscope displays a dot at the center - no chroma info, only lumanance. In this view of the video signal, the luminance is the vector going straight into and out of the screen at the center of the scale. To read more about that at Wikipedia, click the link below the image.
I present this to you to visualize the color relationships. To summarize, the P7 screen images in the photos look grey. They are. This is because both the blue and the yellow light are summing together to produce white light. Or at least as far as the human eye is concerned.
It happens that blue and yellow are primary opposites. Blue is an additve primary while yellow is a subtractive primary color. When two primary opposite colors are mixed, the hues cancel out and only the luminance, or brightness information, remains.
Hence, the appearance of grey scale. This is only valid for still images on P7. Moving images have the most annoying yellow comet tails and blinding bright blue edges. Not good for TV viewing. Perfect for radar. Turned the high voltage down to volts and it worked just fine. Not good for a TV as the beam spot is too large even when focused as well as possible. Still pretty impressive. In the background are the high voltage driver boards and in front of those is my 1EP11 blue phosphor CRT. The second photo is the same set up with my green phosphor 1EP1.
Pictures 3 and 4 are of the scope clock output as it was inteded, driving a high bandwidth XYZ display.
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