the electric vibrators

The vibrator was a device with switch contacts on flexible metal strips. When the vibrator was operated the strips vibrated rapidly in such a way as to make contacts presenting a 6 or 12V DC from the battery in alternating sense, rapidly exchanging positive and negative, effectively generating a square wave(not pure sine wave inverter). Unlike DC, an alternating voltage applied to the terminals of the primary winding of a transformer will induce a different (in practice higher) voltage of any desired value at the secondary; this voltage can be rectified by a thermionic diode or copper-oxide or selenium rectifier, or by an additional set of mechanical contacts making the electric vibrators output a synchronous rectifier. The rectified output is then filtered, ultimately converting a DC voltage to a higher one, with some losses dissipated as heat.

This arrangement is an electromechanical inverter circuit. The electric vibrators switches used for this purpose wore out after a time, so were usually encased in a steel or aluminum can with a plug for easy replacement when mounted in a socket similar to those used for tubes.
 

VB series electric vibrator

electric vibrators