[Milsurplus] FW: [ARC5] Carbon mic pops

[hwhall at compuserve.com]

> It would also be useful to know which    specific equipment you copied the circuit from.  It may have a    history of the problem you have experienced.<

The equipment is a 1943 Link Trainer instructor's desk console.  This circuit provides the amplification of simulated navigation signals as well as simulated radio voice communication between instructor & trainer 'pilot.'  No idea whether they had this pop originally but it is so painfully loud that I tend to doubt it.  Yet from the schematic I don't see how they avoided it, either.

 

 Wayne
WB4OGM


-----Original Message-----
From: Michael Hanz <aaf-radio-1 at aafradio.org>
To: Hubert Miller <Kargo_cult at msn.com>; milsurplus <milsurplus at mailman.qth.net>
Sent: Wed, Nov 30, 2016 7:58 pm
Subject: Re: [Milsurplus] FW: [ARC5] Carbon mic pops


    Hue's questions are salient.  It would also be useful to know which    specific equipment you copied the circuit from.  It may have a    history of the problem you have experienced.
    
    
On 11/30/2016 5:52 PM, Hubert Miller      wrote:
    
    
                        
        
1.                    You            know that if the AC 6v rectified supply to the mic circuit            has no unkeyed current and no regulation, the DC is going to            soar up to 8-9 volts, right?
        
A            zener across the 50 uF cap would lessen the inrush current.
        
2.                    The            microphone current <10 mA seems a little on the low side            but that may be irrelevant.            
        
3.                    I            would try  a cap at the top side ( microphone side ) of the            primary of T-4. The cap will key-up charge to the same            voltage as the 50 uF and will
        
                   ( maybe! ) slow the inrush current by means of its stored            charge. I would try 0.05 uF which is about 3000 ohms at 1000            Hz. You don’t want to go
        
                  higher than 0.1 uF.
        
 
        
Worst            case, a cap across the secondary of T-4 or worser case, even            a zener clipper here.            
        
This            is just my thinking. I don’t have a clue why it was designed            like that or if what you’re experiencing is “normal” for            that equipment.
        
 
        
I            have a Bendix intercom amp ( non-JAN nomenclatured ) which            maybe i’ll have a look at to see how it’s wired.
        
-Hue            
      
      
      
      
      
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