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 |
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low-frequency |
response obtained. |
The |
shield |
should |
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be connected to the chassis. |
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INSTALLATION: |
The 717B Microphone |
is designed |
to |
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be held in the hand. However, the |
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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 |
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Height, Overall. . . . . . . . . . . . . |
6" |
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Height, |
Case . . . . . . . . . . . . . . . . |
2-l/2" |
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Width . |
. . . . . . . . . . . . . . . . |
2-1/2" |
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Thickness . . . . . . . . . . . . . . . . |
1-1/2” |
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Finish . |
. . . . . . . . . . . . . . . . |
Brown |
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Net Weight . . . . . . . . . . . . . . . |
3/8 |
Lb. |
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Shipping Weight. . . . . . . . . . . . . |
3/4 |
Lb. |
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Code Word |
(7’ Cable) . . . . . . . . . . |
RUDUK |
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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.
Copyright Shure Brothers, 1942. |
Printed in U.S.A. |