A simple solution, made according to the diagram shown in the picture below, allows to check whether the filament fiber in the tube is not discontinuoused and to detect specific defects of the tube (eg increasing the resistance of the filament fiber due to defective soldering to the pins of the socket; shorting the fiber inside the bulb or in the socket, e.t.c.).
The device includes:
- power (mains) transformer
(primary winding 110/220V~, secondary - 1,25V~),
- nakelite plate with various sockets mounted on it (2 sockets for a given type of tube),
- current meter (milliammeter),
- rectifier (Pr),
- two wire resistors (5 ohms each),
- two 2-volt indicator buklbs (Lv, Lp).
The operation of the tester is based on the well known bridge principle. After connecting the transformer to the electrical network, and the tubes to the sockets (reference tube V and tube under test P) - if the filament fiber resistance of both tubes are the same - the measuring instrument will not indicate any current flow, and both incandescent bilbs will glow with the same brightness . If, however, the fiber of the tested tube has a higher resistance than the fiber of the reference tube, then the measuring instrument will show the current flow correspondingly smaller, and the bulb in its circuit will shine brighter. This means a defect in the fiber of the tested tube.