Shure 718A User Guide

		DATA SHEET
		D A T E : F E B R U A R Y , 1 9 4 7
	SHURE BROTHERS	S U B J E C T : Model 718A "Versatex" The
	SHURE BROTHERS	Versatile Crystal Microphone.
	INCORPORATED	Versatile Crystal Microphone.
	Microphones and Acoustic Devices

225 WEST HURON STREET :: CHICAGO 10, ILLINOIS P H O N E D e l a w a r e 7 - 4 5 5 0 : : C A B L E : S H U R E M I C R O

Model 718A "Versatex" The Versatile Crystal Microphone

General: Model 718A "Versatex" is an extremely versatile pressure-operated diaphragm type crystal microphone. The "Versatex" is suitable for placement on table top, desk top, or other flat surface; it fits conveniently in the palm of the hand for use as a hand microphone: it is provided with a 5/8"-27 Thread and may be used on a conventional floor stand. The "Versatex" has the typical semi-directional properties.

The crystal used is a Bimorph unit with special-pro- cess moisture proofing.

The microphone is provided with a built-in protective resistor to give increased protection against Radio Frequency burn-outs when used with radio transmitters.

The Model 718A "Versatex" is supplied with a jr-foot shielded plastic-jacketed cable.

Applications: The Model 718A "Versatex" is designed for voice and music reproduction and is ideal for amateur communications, home recording, low cost P.A. systems, call systems, and all general purpose use.

The durable plastic case of the "Versatex" makes this m i c r o p h o n e e s p e c i a l l y s a f e f o r u s e w i t h a m a t e u r equipment.

The cartridge unit is mounted in rubber to provide mechanical isolation from the case, so that the microphone may be handled or carried about without annoying mechanical noise pickup.

Connections: The inner or “hot” conductor of the cable should be connected to the grid of the first tube in the amplifier across a load resistance of 5 megohms. Input resistances as low as 1 megohm may be used if necessary but higher values are recommended because of better low-frequency response obtained. The shield should be connected to the amplifier chassis or ground. The cable may be lengthened if desired; low capacity shielded microphone cable should be used for this purpose.

Operation: No polarizing voltage is required for crystal microphones.

Crystal microphones may be seriously damaged if accidentally connected to loud speaker or power supply outlets carrying high voltage. Check your connections carefully.

Crystal microphones should not be used or kept in places where the temperature exceeds 125°F. They should not be exposed to the rays of the sun in very hot weather for any considerable length of time-or left in closed automobiles parked in the sun during hot weather, as the temperature inside the automobile may easily build up to over 125° and permanently damage the crystal.

When used near a radio transmitter, use the minimum length of cable consistent with placement requirements. Careful grounding of the cable shield is advisable.

27A29 (11 48)

	SPECIFICATIONS

. .Model	. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	718A

Height, Overall . . . . . . . . . . . . . . . . . . . . . . . . .		5-7/8"

Diameter	at Base . . . . . . . . . . . . . . . . . . . . . . . . . . .	2-19/32"

Finish . . .	. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	Maroon

Net Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		5/8 lb.

Shipping	Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . .	1-1/2 lb.

Code Word (7' Cable). . . . . . . . . . . . . . . . . . . . . . . .		RUTEX

Voltage Sensitivity: 2.2 millivolts r.m.s. per bar at the end of a 7-foot cable across 1 to 5 megohms at 400 cycles. This is equivalent to 53 db below 1 volt per bar at the terminals of the 7-foot cable.

Internal Output Impedance: Equivalent to a

900 micro-microfarad condenser.

Recommended Load Impedance: 1 to 5 megohms.

Guarantee: Each microphone is guaranteed to be free from electrical end mechanical defects for a period of one year from date of shipment from the factory, provided all instructions are complied with fully. In case of damage, return the microphone to the factory for repairs. Our guarantee is voided if the microphone case is opened.

License Notice: Shure patents pending. Licensed under patents of the Brush Development Company.

Printed in U. S. A.