A method for measuring the filament voltage of a kinescope. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Телевидение
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On the pages of the magazine, many different devices for preheating cathodes of a kinescope were considered before applying high voltage to the anode. In almost all the devices described earlier, after such a warm-up, the factory inclusion of the filament is restored. However, in my opinion, it does not take into account the fact that when the filament voltage is higher than the nominal (6,3 V) by at least 0,2 ... 0,3 V, the service life of the kinescope is significantly reduced.
It is no coincidence that overvoltage is considered the main reason for the failure of kinescopes before the expiration of the warranty period. Therefore, it is necessary to strictly control the value of the voltage applied to the filament. Given that the shape of the kinescope filament current is far from sinusoidal, conventional voltmeters are not suitable for measurement in this case.
For this purpose, I propose the simplest attachment to any ohmmeter, which allows you to measure the effective value of voltage of any form with quite sufficient accuracy.
The schematic diagram of the device is shown in the figure. OEP-13 optocoupler can be replaced with OEP-9 - OEP-12. Resistor R1 is selected so that the input voltage at the optocoupler does not exceed the passport value, in our case it is 5,8 V.
The prefix is calibrated when a constant stabilized voltage is applied to the input with simultaneous measurement of the output impedance of the optocoupler. In the case of using the attachment to control only the filament voltage of the kinescope, it is enough to calibrate it at one point (6,3 V).
Author: S.Zhemkov, Oktyabrsky, Bashkortostan
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