A device for soft non-contact inclusion of a kinescope. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Телевидение
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In our magazine and other radio engineering literature, many descriptions of a wide variety of devices have been published that protect the kinescope from premature failure when the TV is turned on. An interesting version of another such device using a kenotron is considered in the material published here.
To protect the filament of the kinescope when the TV is turned on and to ensure the gradual heating of the cathode (cathodes) of the tube, a non-contact device is proposed, the circuit of which is shown in the figure.
It is a variant of the limitation and delay assembly, in which a lamp diode (kenotron) VL1 is used to limit the filament voltage when the delay for supplying its full value is turned on. Transformer T1 matches the resistance of the filament circuits of the kinescope and diode VL1.
The primary winding of the transformer is included in the filament circuit of the kinescope. A rectifier bridge VD1 is connected to the secondary boost winding, loaded on the VL1 kenotron and providing, with the VL1 diode closed, an output voltage of 220 ... 240 V for some time after the power is turned on. ).
At the moment the TV is turned on, the voltage on the filament of the kinescope, due to a drop in the inductive resistance of the primary winding of the transformer T1, is reduced to about 3,25 V at a current of about 0,4 A. Within 18 seconds, as a result of the gradual heating of the cathode of the VL1 lamp, it appears and increases to 30 mA current through it. The kenotron shunts the secondary winding of the transformer T1 through the diode bridge. At the same time, the voltage of the kinescope filament rises to 6,3 V at a current of 0,8 ... 0,9 A. The voltage at the output of the diode bridge VD1 smoothly drops to 5 V within 25 s due to the shunt effect of the lamp diode VL1.
The decay time of the kinescope-closing voltage depends on the time constant of the kinescope modulator circuit, i.e., mainly on the capacitance of capacitor C1. Diode VD2 plays the role of separating between the time-setting circuits of the filament and the kinescope modulator.
As a matching device, the output sound transformer from the Raduga-703 TV was used. To ensure automatic regulation, it is necessary to raise the voltage on the filament winding of the power transformer to a value of 8,4 V by winding an additional winding over one of the power transformer coils. This winding, containing five turns of PEV-1 wire with a diameter of 0,55 mm, is connected in series and in-phase main.
Author: A. Zhadobin, Moscow
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