[ARC5] T-17 Microphone

[Richard Knoppow]

----- Original Message ----- 
From: "Mark K3MSB" <mark.k3msb at gmail.com>
To: "Kenneth G Gordon" <kgordon2006 at frontier.com>
Cc: "ARC5" <arc5 at mailman.qth.net>
Sent: Wednesday, June 11, 2014 5:12 PM
Subject: Re: [ARC5] T-17 Microphone


> Aw fer..... sigh....... sometimes I just don't dig deep 
> enough.
>
> When I was putting the mic back in the box I decided to 
> pry the mic element
> out.  It's a modern "American D-30 Dynamic Hi-Z made in 
> Japan" mic head,
> and that is probably a hi-z to lo-z modern JA matching 
> tranny....
>
> So, bulletin.... bulletin.... bulletin.... it's not NIB at 
> all....
>
> 73 Mark K3MSB
>
    Caught up on this late, that is after digging out my 
T-17.  I was puzzled about the transformer because carbon 
microphones don't have them, at least not built-in.
    Mine barely works while I have another, a sort of 
mushroom shaped mic, that works perfectly but must be of 
similar age.  My T-17 also has a rotting cable. The great 
enemy of carbon mics is moisture. Sometimes its possible to 
dry them out by baking but it does not always work. The 
other thing that kills carbon mics is excessive current. 
That causes the corners of the carbon particles to weld 
together. Sometimes a good shake will help but if the 
current was high enough the carbon is changed somehow and 
can't be salvaged.  I have been able in the past to repair 
some old broadcast type carbon mics with the carbon from 
telephone microphones but the telco carbon is usually a bit 
coarser.
     One of the most thoroughly engineered microphones ever 
was the microphone in the Bell System 500 series handset. It 
was designed to be pretty much moisture proof and made to 
operate in any position where most carbon mics are quite 
position sensitive.
     Carbon mics were popular for a very long time because 
they are essentially amplifiers and will put out very high 
levels without electronic amplification.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com