From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Specification document for a rectifying valve used in high tension DC insulation testing or ball gap voltage measurement.
| Identifier | ExFiles\Box 60\2\ Scan073 | |
| Date | 17th February 1931 | |
| SPECIFICATION OF RECTIFYING VALVE FOR H.T. D.C. INSULATION TESTING OR BALL CAP VOLTAGE MEASUREMENT. A suitable filament voltage would be 5.5 to 6.0. The purpose for which the valve is required (for instance, insulation testing and high D.C. voltage measurement by accumulating a charge on a H.T. condenser with a sphere gap voltmeter in parallel) does not demand any more than a very small milliampere output, in fact this output need never exceed one milliampere in any circumstances. The purpose, however, does demand that the valve will stand up to a very high reverse voltage namely 12,000 volts negative of the plate to the filament. We can define the anode filament impedance indirectly by saying that the valve must be approximately such that an alternating voltage with a peak value of 6,000 can be applied to the plate in relation to the filament. On open circuit, with a condenser (without leak) to hold the rectified charge, the reverse voltage will then be 12,000. Assuming the condenser now to be short circuited, the maximum voltage from the plate to filament will be ± 6,000 and the effect of the positive half waves of this voltage should be such as to pass an electron current not exceeding one milliampere. Since the average voltage is 6,000/π i.e. approximately 2,000 it will be seen that a rough estimate of the impedance is two million ohms. Note. With regard to the particulars of the G.E.C. U.3 valve, this had a rated total filament emission of 80 milliamperes and a rated reverse pressure, filament to plate of 3,000 volts only. The filament voltage was 5.5 to 6. We were able to use this valve in connection with insulation testing at moderately high voltages but it was not entirely satisfactory at the voltages we wished to use in that the static attraction of the reverse plate pressure for the filament caused the filament to bow and ultimately | ||