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The what and
the why of Wireless Set No.19 Microphones.
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In the past there has been some discussion and confusion about what
microphones work with the 19 set. This is a There are two possible types of microphones that were used with the
19 set: dynamic and differential carbon granule. The dynamic is the familiar Microphone, Hand, No. 7 with the rubber
noise exclusion cone which is part of the The carbon granule is Microphone, Hand, Power No. 1A and is part of
the Microphone and Receiver Headgear No. The control boxes are of three types: Those that provide no power to the microphone and contain no transformer.
These will ONLY work with the Those without any snatch plugs, such as the #10. Since there is no microphone connection, the type is moot. Those that can provide power to the microphone, the Junction Distribution Boxes #1 and #2. These are identical save for the provision of a call buzzer in the #1. These boxes will work with EITHER headset as follows: If used with the dynamic microphone, the microphone output on pins 4
& 5 of the snatch plug is coupled to the set If, however, the carbon microphone is used, the operation is as follows.
The vehicle +12 VDC is connected to the A) Motion off centre of the diaphragm makes the resistance of one capsule
go up and the other go down, producing B) The DC current in the two halves of the transformer primary cancel
each other so the transformer core does not C) The powered microphone has gain, so it can work without the IC amplifier. NOTE: The Junction Distribution boxes have no ability to key either transmitter. They ONLY provide an internal communication facility for the AFV. So, what does this all mean? **************************************************************************************** The dynamic mike will work with any control box. The carbon mike(Microphone & Receiver Headgear #2)will ONLY work with Junction Distribution Boxes #1 & #2 **************************************************************************************** By the way, you can test your dynamic microphone simply with a 'scope or the IC function on your 19 set. For the scope, just look at the output of the capsule, or at the snatch
plug, or at the terminal strip in the control box (this is the easiest).
Speak into the mike and you should see voltage. The pinouts are in the
Working Instructions or in To use the set, just switch your headset to IC. Press the presstle switch
and speak into the mike. If you hear yourself, Alister Mitchell. |
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Site and all files are copyright © 2004 - 2012 Keith Watt RN, MRCN & Alister Mitchell. |