Rugged ABS Plastic Casing Integrated circuit amplifier including amplifier with frequency response adjusted for best voice articulation Integrated circuit oscillator AC or DC operation with selectable timing P.O door lock release The PK-543A Power Pack Intercom Amplifier is a self contained unit not requiring an external amplifier. The PK-543A is designed for use with most 3-4-5 wire apartment stations and provides amplification control and power circuits needed to operate a complete apartment intercom system. Voice volume control and tone volume control are easily adjustable through the screwdriver slot on the front panel. Additional functions include multi-entrance operation with the PK-502B, AC or DC door operation selectable by terminal connection with selectable delayed action door release set at the dip switch, post office door lock release and a tone signal to call remote stations. A steady or warble tone can be used to identify calling from the main entrance panel and a call button located at the suite entrance.