Patent GB-481601-A (GB)
Title: Improvements in or relating to apparatus for testing thermionic valves
IPC: G01R31/25
Filed: 1936-08-24
Abstract: 481,601. Current and voltage measurements; indicating faults. COOPER, A. H. Aug. 24, 1936, No. 23208. [Class 37] Apparatus for testing thermionic valves has switches or controls which are pre-set according to indications on a card 31 corresponding to the type of valve under test and are then switched in in predetermined order by means of a master control switch 37, the condition of the valve or its electrodes being caused to control the actuating current in a " good " or " bad " indicating device. The apparatus is housed in a cabinet 20 along the top of which are arranged a plurality of valve holders 21 for valves having different numbers of pins. Cap terminals 22 carried by extensible spring- retracted leads are provided for valves having external top connections. The master switch 37 changes the connections so as to carry out in succession tests for continuity of filament or heater, electrode insulation, electrode continuity, emission from cathode, amplification, and state of vacuum. The test being carried out is indicated by the illumination of the corresponding section of the upper half 25 of a panel 24, the lower half of which is divided into two sections 26, 27 which are illuminated to give " good " and " bad " indications respectively. On the spindle of the switch 37 is a drum 38 bearing indications as to the steps to be followed in the testing of a valve as the switch 37 is operated. Three controls 28, 29, 30 are pre-set for the particular kind of valve under test in accordance with markings on the card 31, which is apertured to fit over them. This card also covers twenty-seven sockets 32 arranged in nine rows of three, and has nine perforations registering with one socket in each row. Plugs 33 are inserted through the perforations to make the necessary connections to the electrodes. Blank sockets 34 are provided for receiving the plugs when not in use. A switch 40 is used in conjunction with the plug sockets to present the electrodes of the valve successively for test. Each of the switches 37, 40 has a large number of contacts wiped by a bank of rotating contacts. A front panel 41, normally covered, carries controls and switches for calibrating the apparatus. A voltmeter 42, main switch 43, and plug connector 44 are provided. A jack 172 enables an external milliammeter to be plugged in to measure the emission. For carrying out the tests for continuity of filament and electrodes, electrode insulation, amplification, and vacuum, the circuits are such that the grid bias of a testing valve in the apparatus is controlled by the valve under test so that a relay in the anode circuit of the testing valve causes the illumination of the appropriate "good" " or " bad " indicator 26, 27. When testing for emission, the indicating relay is connected in the anode circuit of the valve under test and is shunted by a resistance which is pre-set to a value appropriate to the valve by setting the control knob 28 in accordance with the marking on the card 31. The control knobs 29, 30 when set to their appropriate marks pre-set the voltage applied to the filament and the change in grid potential during the amplification test. Switches may be employed instead of the sockets 32 and plugs 33. The apparatus is operated by alternating current and contains the necessary transformer, rectifiers, and smoothing chokes and condensers. A control knob 211 enables different supply voltages to be employed. The apparatus may also be set to test insulation or to detect small currents, or for use as a valve voltmeter if the indicating relay is set to operate within the required current limits.