[ARC5] Carbon mic pops

[hwhall at compuserve.com]

There are no mods, all agrees with the 1940's government schematics. I've been wondering if a modified mic was supposed to be used but the parts lists don't cite anything special.

In this unit, there aren't any relays that need tripping like in a transmitter, so one pair of the T-17 contacts do nothing & the other pair connects the mic button to the DC source.  I'm thinking the pop is from the mic's DC suddenly appearing on the amplifier grid.  I'll try to get a schematic up for y'all to look over.

 

 Wayne

 

-----Original Message-----
From: J Mcvey <ac2eu at yahoo.com>
To: hwhall <hwhall at compuserve.com>; arc5 <arc5 at mailman.qth.net>; milsurplus <milsurplus at mailman.qth.net>
Sent: Tue, Nov 29, 2016 7:46 am
Subject: Re: [ARC5] Carbon mic pops



All of those carbon mike circuits were very similar in design back then. I have never encountered one that "popped" as you describe.
This makes me wonder if there was some unknown mod done to the mike or the preamp circuit. I've seen some sites where they replace the carbon element with electret
mike elements. I don't know how well that works- maybe its fine, but I always used carbon types with no problems.


Try engaging the PTT without the mike in circuit to see if you still get the noise. it could be from some other source further down the chain...


 



 
 
 
 On Monday, November 28, 2016 10:17 PM, "hwhall at compuserve.com" <hwhall at compuserve.com> wrote:

  

 

All the caps were replaced before we powered up. The "battery" DC power supply is quiet, no hum with the PTT held down. Just a loud pop when the PTT contacts close.
 

 Wayne

 


-----Original Message-----
From: J Mcvey <ac2eu at yahoo.com>
To: hwhall <hwhall at compuserve.com>; arc5 <arc5 at mailman.qth.net>; milsurplus <milsurplus at mailman.qth.net>
Sent: Mon, Nov 28, 2016 8:03 pm
Subject: Re: [ARC5] Carbon mic pops



My guess is that you have an open cap in the Mic DC filter circuit. 

 



 
 
 
 On Monday, November 28, 2016 9:53 PM, "hwhall at compuserve.com" <hwhall at compuserve.com> wrote:

  

 
I have a question about use of carbon mics in circuits like interphones. Mics like the T-17 leave the mic "battery" current circuit open until the PTT is pressed to speak. But the contact closure creates a huge pop in the headphones attached to the amp output. Does anyone know how this was dealt with or did they just live with the earsplitting pops??

Wayne
WB4OGM


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