Old-stock device. A PUT can be used anywhere that a unijunction would be, and it is more flexible because its characteristics can be set by external resistors. The datasheet can be found here. Works similar to a 2N6027, but the pinout is K G A rather than A G K. Typically used as a less-expensive alternate to the 2N2646 in a repeat percussion device. Build the Moosapotamus Skippy or try this idea using a photocoupler as the modulator.