Abstract: A dynamic microphone and dynamic microphone amplifier used with a pay station telephone system has the amplifier physically located within a pay station and includes an isolation transformer to prevent ground faults in the dynamic microphone in the handset from being sensed by telephone network control circuitry. The dynamic microphone amplifier is mounted on a printed circuit board which includes an isolation transformer for the speaker element in the receiver of the handset. The leads from the transmitter dynamic microphone and receiver speaker are connected to the amplifier circuit board by way of a modular pin connector physically located in the pay station housing. The isolation transformers function as ground fault isolation devices to prevent ground faults in the handset from affecting the operation of the associated telephone system and to reduce the risk of electrric shock to a user.

Abstract: A tubular-shaped spirit vial is provided which is capable of being illuminated at its ends, offering improved observation of the spirit bubble location. The spirit vial has particular application in carpenter's and other tradesperson's levels providing greater ease in making, and more accurate, horizontal and vertical level determinations in poorly lighted work areas and against dark wood.