Shure 717B User Guide

DATA SHEET No. 136

DATE: August, 1944

SUBJECT: Model 717B

Crystal Hand Microphone

MODEL 717B CRYSTAL HAND MICROPHONE

GENERAL: Model 717B is a pressure-actuated dia-

phragm-type semi-directional crystal microphone with wide range response for

high quality reproduction of sound. The crystal used is a grafoil (high capacity) bimorph unit, moisture-sealed to withstand adverse climatic conditions. The microphone is provided with a 7-foot shielded rubberjacketed cable.

APPLICATIONS: The Model 717B is designed for announcing, home recording and all general purpose use. The frequency

response	is suitable for	either	voice	or music,	and
is free	from undesirable	peaks.	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 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 becauseof the better
low-frequency	response obtained.	The	shield	should
be connected to the chassis.
INSTALLATION:	The 717B Microphone		is designed		to
	be held in the hand. However, the
	Microphone may	be mounted		in	the

amplifier cabinet through the use or a No. 47-54 clip or it may be fastened in a No. 99-120 stand for table use.

OPERATION: No polarizing voltage is required for crystal microphones.

Crystal microphones may be seriously damaged if accidently 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 exposedto 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° end 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.

SPECIFICATIONS

Voltage Sensitivity: 2.2 millivolts r.m.s.

bar at the and 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 1,500 micromicrofarad condenser.

Recommended Load

Impedance : 1 to 5 megohms.

SPECIFICATIONS-Continued

.Model	. . . . . . . . . . . . . . . .	717B
Height, Overall. . . . . . . . . . . . .		6"

Height,	Case . . . . . . . . . . . . . . . .	2-l/2"

Width .	. . . . . . . . . . . . . . . .	2-1/2"

Thickness . . . . . . . . . . . . . . . .		1-1/2”

Finish .	. . . . . . . . . . . . . . . .	Brown

Net Weight . . . . . . . . . . . . . . .		3/8	Lb.

Shipping Weight. . . . . . . . . . . . .		3/4	Lb.

Code Word	(7’ Cable) . . . . . . . . . .	RUDUK

GUARANTEE: Each microphone is guaranteed to be free from electrical and mechanical defects for a period of one year from

date of shipment from the factory, provided all instructions are complied with fully. In case or damage, return the microphone to the factory for repairs. Our guarantee is voided it the microphone case is opened.

LICENSE NOTICE: Shure patents pending. Licensed under patents of the Brush Development Company.

Printed in U.S.A.