Abstract: A modular hearing aid to fit in the user's ear, having a shell, a faceplate fixed to the shell, and an electronic module removably snapped into the faceplate. The module includes an open-topped battery compartment which is closed by a lid hinged to the faceplate rather than to the module. This eliminates a bulky hinge on the module and allows a smaller snap fastener between the module and faceplate. The volume control on the module projects through an opening in the closed lid.

Abstract: A method for producing a vent passage for an in-the-ear hearing aid shell. One or more vent holes are drilled in the shell, and a vent tubing having a copper core is laid against the shell interior wall extending through the vent holes. Electricity is passed through the core to heat the vent tubing rapidly (e.g. within 15 seconds) to 60.degree. C. Simultaneously with the heating, acrylic monomer and polymer are mixed. The mixture is poured promptly into the shell over the tubing, and excess mixture is then poured out, after which the coating on the tubing is cured and the tubing is removed. The rapid heating causes onset of polymerization adjacent the tubing but not elsewhere, so that a very compact vent passage is formed with minimal labor and little excess acrylic polymerization in unwanted areas. The heating is performed using a fixture having clamping plates mounted on a rod.

Abstract: A modular hearing aid to fit in the user's ear, having a shell, a faceplate fixed to the shell, and an electronic module removably snapped into the faceplate. The module includes an open-topped battery compartment which is closed by a lid hinged to the faceplate rather than to the module. This eliminates a bulky hinge on the module and allows a smaller snap fastener between the module and faceplate. The volume control on the module projects through an opening in the closed lid.

Abstract: An inverter circuit for a power train has a rectifier for rectifying a three phase AC input and a filter comprising an inductor and capacitor to produce a filtered DC signal for application to the inverter. A high to low voltage transducer receives the filtered DC signal to produce a low voltage output representation thereof. A leading phase shifter shifts the low voltage signal in phase. A sample and hold amplifier receives shifted signal, and a pulse generator generates timing pulses applied to the sample and volt amplifier, whereby the sample and hold amplifier produces an output signal amplitude corresponding to the amplitude of the shifted signal during periods indicated by the pulse generator output. A triangle wave generator provides a triangle wave output to a pulse width modulator, which also receives the output from the sample and hold amplifier to produce an output pulse indicative of the signal level of the filtered DC output.

Abstract: A wax guard for a hearing aid is mushroom-shaped, having a cross passage through its head which intersects an axial passage in its stem. The axial passage contains an acoustic filter terminating the axial passage in its characteristic impedance. The cross passage is semi-circular in section to reduce the projection of the guard into an ear canal and the total area of the two branches of the passage exiting from the axial passage is equal to that of the axial passage. The guard removably snap fits into a metal ring glued into the outlet port of the hearing aid.

Abstract: A connecting cord has a plug at each end. Either such plug may be plugged into the receptacle of a hearing aid and the other plug may be plugged into an external microphone. The contacts of each plug are connected in a different circuit configuration to the conductors of the cord so that when one plug is plugged into the receptacle, the internal hearing aid microphone is shorted out, and when the other plug is plugged into the receptacle, both microphones operate in parallel. The plug contacts are formed of printed circuit board and each plug has a rocker with a hooked top which engages a slot in the receptacle to prevent the inadvertent movement of the plug out of the receptacle. Other plug internal circuit configurations allow connection of other signalling systems to the hearing aid.

Abstract: An acoustical damping element for acoustical tubing such as a hearing aid earpiece, in which a disc of wire screen is positioned over a disc of flexible fabric of a selected acoustic resistance, over the mouth of the tubing. An insertion tool of diameter slightly less than that of the interior passage of the tubing then pushes the composite layers of screen and fabric into the tubing, thereby forming the screen and fabric into closed end concentric cylinders in the passage. The cylindrical sidewall of the screen presses the cylindrical sidewall of the fabric against the interior wall of the tubing to retain the damping element within the passage.

Abstract: A high frequency battery charger operable from a 120 volt AC line power source which is rectified and converted by a blocking oscillator into 20-200 Khz rectified output for battery charging. A sensor for determining full battery charge serves as a power cut off to the battery with provision, if desired, for continued trickle charge of the battery.

Abstract: A power oscillator utilizing one or more field effect transistors in conjunction with a tank circuit.

Abstract: A hearing aid having a two port microphone for adjustable directivity. The microphone front port is connected to a front port in the casing by a soft resilient rubber tube. The microphone rear port is connected by another soft resilient rubber tube to an outlet in the top of the casing, which outlet is covered by a slider. The slider has a channel communicating with the outlet and having front and rear openings separated by a divider wall. Depending on the position of the slider, the outlet connects with either the front or rear channel opening, controlling the directivity of the aid. The microphone is supported by the rubber tubes, which isolate it from the remainder of the aid.

Abstract: A high frequency power supply with inductive coupling and a SCR starter to light two fluorescent lamps is described. It supplies high frequency square waves to the fluorescent lamp for improved light output, efficiency and stability of operation. The rectified line voltage from a full wave rectifier is fed via a SCR starter to two transistors that form an inverter circuit. The inverter circuit is coupled to a ferrite core autotransformer. The secondary windings of the autotransformer are used to heat the filaments of the electrodes of the fluorescent lamp, and to form a reactive coupling along with inductors for stabilizing the arc discharge of the fluorescent lamp.