[ARC5] [Milsurplus] Carbon mic pops

[hwhall at compuserve.com]

>Are the two mike filter capacitors originally 50uF? 

Yes, that's what was on schematic & what was found installed. Restuffed them with 47uF new ones.


>
Since "new" capacitors are so much better then what was used originally, I wonder if you paralleled the caps with high value resistors, would this would reduce the pop?  Perhaps a resistor value that would cause 1/10 the microphone current to leak around the caps?
>


Never thought about that, Jim & it seems sort of counterintuitive, so I probably wouldn't have. But that wouldn't cause a current thru the T-4 primary, so when the mic is keyed there's still be a sudden current in the windings & a transient out the secondary side (the pop). 

If there was constant current thru the primary, with the mic element getting switched in & out of that current, it might make a difference. But there's apparently no provision for that kind of switching. I'd thought once about whether the mic's contacts could be rewired as a short across the mic element, so that current always flowed, & the short opened only when you wanted to talk, but the T-17 contacts aren't put together that way.

Wayne

 WB4OGM

 

-----Original Message-----
From: antqradio <antqradio at sbcglobal.net>
To: milsurplus <milsurplus at mailman.qth.net>
Sent: Wed, Nov 30, 2016 10:05 am
Subject: Re: [Milsurplus] [ARC5] Carbon mic pops



Wayne
Are the two mike filter capacitors originally 50uF?  
Since "new" capacitors are so much better then what was used originally, I wonder if you paralleled the caps with high value resistors, would this would reduce the pop?  Perhaps a resistor value that would cause 1/10 the microphone current to leak around the caps?
Jim



  
 
 
  
 From: "hwhall at compuserve.com" <hwhall at compuserve.com>
 To: arc5 at mailman.qth.net; milsurplus at mailman.qth.net 
 Sent: Wednesday, November 30, 2016 12:44 AM
 Subject: Re: [Milsurplus] [ARC5] Carbon mic pops
  
 



Attached is the schematic of the mic circuit & amp that I'm looking at. The mic internal wiring looks like just a set of PTT contacts in series with the carbon mic button + the small cap across the mic button.

The primary of T-4 has no current thru it until one of the mics is keyed, then suddenly current flows thru primary & carbon mic, inducing a transient in T-4 that appears as a loud initial pop in the headphones. I don't see how they prevented this pop from happening every time a mic was keyed.

By hitting Send I'm about to remind myself whether these forums allow images attached.  :-\







Wayne
WB4OGM











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