Recently because of frequent cases of so-called "fan" power outages are becoming urgent problem of operational control the presence of voltage in a lighting network. In "Radio" have already been published descriptions of devices such appointments on chips.

Offer a simple variant of the indicator on the thyratron cold cathode MTH. The device (see figure) is a relaxation oscillator the thyratron VL1 powered from the mains via the rectifier diode VD2. Oxide the capacitor C2 smoothes the ripple of the supply voltage. He also serves as power source for a generator in case of loss of voltage in the network.

Audio indicator of loss of mains voltage

When the voltage present at the grid of the thyratron through the resistor R6 served rectified by the diode negative voltage VD1, which breaks oscillation of the relaxation oscillator. When power outage the capacitor C1 is discharged much faster than the capacitor C2. Disrupting the generation the voltage on the grid disappears, and in the dynamic head HA1 within 15...20 s you hear the sound gradually descending tone.

The entire device can be assembled in the housing of a compact subscription the loudspeaker, using the existing dynamic head, matching transformer and a variable resistor.

Before installing in the device the thyratron subjected to "training" for a period of not less than 24 hours To do this, it serves a constant voltage of 200...300 V through resistor of approximately 100 kω, pre-closing the cathode and the grid. This procedure is permissible to do that directly in the device, by connecting the anode thyratron with the right (under the scheme) terminal of the resistor R3.

Establishing device is limited to regulation trimpot resistor R4 when input AC voltage in the range of 200...240 V detector should "be silent", and when power is lost - popping sound. Variable resistor R7 sets the desired volume.

When there is too much delay on the device it is possible to reduce the capacity the capacitor C1 to 0.33-0.47 µf. If the unit is unstable, choose the resistance of the resistor R5.

In case you can cut a hole under the cap of the thyratron, then its glow will further signal the presence of mains voltage.

When establishing the device you should be careful because his chain have a galvanic connection to the mains supply.

Author: Andrei Sharonov, Chita

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