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The D5-194GH is a small rectangular screen precision oscilloscope tube with built-in graticule, intended for small portable wide-band oscilloscopes.
It is an improved version of the earlier D5-192 tube. It is internally aluminised unlike the D5-192. This improves the screen efficiency and brightness and makes it less susceptible to interference from external fields. In common with most oscilloscope tubes it has electrostatic deflection and focussing. The external coil assembly is a trace rotation coil which allows the entire trace to be precisely aligned with the graticule without affecting the deflection or focussing.
The EHT requirement is around 3 kV and the heater runs at 6.3 Volts. The screen has a fairly short persistence blue-white phosphor.
The tube face is optically flat with the graticule printed on the glass before the phosphor coating is applied. No parallax errors here! The face measures 82  x 69 mm.
The gun components. Starting on the right with the heater and flat cathode the electrons pass through the grid plate, first anode, second anode cylinder and third anode before the beam passes through the Y plates. The three anodes form an electron lens that brings the beam to a sharp focus on the screen.
The trace rotation coil is held in place around the neck of the tube by the plastic tape. The EHT connector near the face is for the PDA (post deflection acceleration) coating. In early oscilloscope tubes there was a trade off between a bright trace and deflection sensitivity. The faster the speed of the electrons, higher EHT, the brighter the trace but to deflect fast moving electrons required more power from the deflection amplifiers and this was both expensive and difficult to achieve. With PDA a low speed electron beam is deflected electro-statically in the gun and then the beam comes under the influence of the high EHT voltage and the beam energy is raised and so the energy available to be converted to light is greater allowing for a bright trace on the screen.
The complete tube. The gun components are held in the correct alignment in the neck by the spring against the glass.
The 14 pin base. Within the neck the anode plates are fixed into glass rods.
The end window envelope is 51 mm in diameter, and excluding the base pins is 200 mm tall.
Reference: Observation.


Updated June 21, 2013.
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