Video circuits


Posted on Feb 7, 2014

This page describes the development of electronics to display a monochrome video image on an electrostatic oscilloscope tube. This work is complementary to the Electron Optics page in the Experiments section. The ultimate goal is to display a moving video picture on a completely home made cathode ray gun inside the bell jar of a vacuum rig. For th


Video circuits
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is reason I chose to use a 1950`s RCA 3RP1-A oscilloscope tube. It is very similar in specification to my homemade electron gun and so is well suited to the development of the electronics. It should ultimately be possible to disconnect the RCA tube and connect the homemade one. The circuit is designed for use with a PAL composite video signal, but it should be possible to adapt it for use with NTSC or SECAM by changing a few component values. In particular, the ramp rates of the sweep integrators may need to be adjusted slightly. I chose to use a Sanyo LA7801 synchronization and deflection IC. This was the most suitable part in my bits box for which I could obtain a data sheet. This part is obsolete but could probably be obtained from an old television. Other timebase ICs could be used with appropriate alteration of the circuit. The circuit is closely based upon that provided in the data sheet. Click on the schematic below to see it in higher resolution. The line pulse output at pin 4 of the LA7801 consists of a 2V, 25us long positive rectangular pulse. The rising edge coincides with the start of the line. The field pulse output at pin 6 consists of a 3V, 1. 5ms long positive rectangular pulse which coincides with the field blanking period. The integrators (below) ramp freely until reset by the FETs (TR1 and TR2). This gives the required `saw tooth` sweep waveforms. One PAL line lasts 64us, so the horizontal integrator...




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