Device for testing electron tubes - Przyrząd do badania lamp (Radio dla Techników i Amatorów 1949/10)
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Device for testing electron tubes
(Radio dla techników i Amatorów, Październik 1949, Rok IV, Nr 10)
In our monthly magazine, we have not yet described an important and basic instrument, which is the practice of a radio amateur and radio technician - a device for testing electric lamps. Twice, however, such a device was described by our brotherly weekly "Radio i Świat", namely in 1945 No. 15 entitled "Instrument for testing the emission of electron tubes" and in 1947 No. 36/37 entitled "Instrument for testing electron tubes". Both of these apparatuses made use of the same principle, shown in Fig.1. The mains transformer has a secondary winding of the filament of the vacuum tube and some additional winding giving an effective voltage of up to 20 volts. The end of this winding is connected, through a limiting resistance of 500 ohms, protecting against the effects of possible short circuits or overloads, and a DC milliammeter - to the anode and other high-voltage electrodes of the tested electron tube. Other electrodes, such as the control grid, are shorted to the cathode, which in turn has a common point with one glow pole. When a vacuum tube is inserted into a suitable socket, a one-way current will flow through it after heating up and cause the milliammeter to deflect. The above mentioned descriptions are accompanied by tables of "normal" deflections of more electron tubes.
Fig. 1. Principle of operation of the most primitive device for testing electron tubes. All electrodes are connected either to the anode or to the cathode. A one-way rectification system is obtained, and the device measures the rectified current, which depends to some extent on the emissivity of the cathode. The shortcomings of this instrument are discussed in the text.
Instruments of the type shown in Fig. 1 operate on the principle of one-way rectification. Each electron tube, regardless of its proper purpose, is of course capable of rectifying, and it does so in a manner dependent to some extent on its "emission". Of course, there is no need to emphasize that the system in which we examine vacuum tubes is not even roughly similar to the conditions in which the vacuum tubes we use work in amplifiers, receivers, oscillators, etc. It even happens that we do not see a case at all any vacuum tube was ever supposed to work under such or even similar conditions.
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