12QR51 picture tube

A picture tube for oscilloscopes, 12 cm diameter, green phosphor with long afterglow. As opposed to TV picture tubes, which draw a rectangular pattern and the image is created by beam brightness variation (raster display), the oscilloscope tubes use electrostatic beam deflection instead of the electromagnetic one, the beam intensity is constant and the image is created by beam path variation (vector display). The picture tube contains two pairs of deflection electrodes, one for vertical and one for horizontal deflection. The deflection is controlled by a voltage difference between each two electrodes. This principle enables linear deflection ranging from static display to the highest speeds, but the deflection sensitivity is much lower than with electromagnetic principle and that's why the tube is so long.