[Boatanchors] [Milsurplus] T-17 microphone

[hwhall at compuserve.com]

I checked the mike case with a good caliper and the largest diameter (after removing the thin insulating ring that separated the mike element from the case) is 1.788 inches, so I would indeed have to modify the case to fit the standard T-1 telephone element.

The AudioSears website shows some carbon elements available and two are smaller in diameter than the T-1 (which is listed as 1.814 inch on some websites). Here's two that look interesting:
#1277 is listed as a 40 ohm mike, 1.227 in dia, 0.375 inch thick, sensitivity -28 +/- 6 dBv.
#1628 is listed as a 15-60 ohm mike, 1.281 in dia, 0.39 in thick, sensitivity -22.5 +/- 5 dBv.
They can be seen here:
http://www.audiosears.com/products/data/mics/index.html

For comparison their #1583C, described as a T-1 type, has sensitivity -23 +/- 4 dBv. That makes it seem like the #1628 is a bit more sensitive than a T-1 and the #1277 a bit less so. However, the range of sensitivity is great enough that examples of each may be indistinguishable in actual sensitivity.

 

 Anyone with experience using either of those two types? Maybe I should experiment?

Wayne
WB4OGM

PS - the dBv is supposed to be decibels relative to 1 volt for a given sound pressure level applied to the mike.

 

-----Original Message-----
From: Mike Hanz <aaf-radio-1 at aafradio.org>
To: hwhall <hwhall at compuserve.com>; boatanchors <boatanchors at mailman.qth.net>; milsurplus <milsurplus at mailman.qth.net>
Sent: Thu, Aug 28, 2014 12:15 pm
Subject: Re: [Milsurplus] [Boatanchors]  T-17 microphone


And the outside diameter of the stack of late WECO drop-in elements I 
have around here is 1.820" (not sure if they are F1s, but the date code 
on them is the _late_ 1960s/early 70s and they have screw terminals for 
connection), which simply requires a small counterbored enlargement of 
the T-17 on a milling machine for a perfect fit.  It takes longer to 
fixture and zero the T-17 in the mill than it does to bore it out.  Done 
it numerous times - as did the old timers.  It could be done with a 
1-13/16" hole saw on a drill press if you don't have a friend with a 
mill, but will require the same careful clamping of the microphone 
body.  I use some resilient vise inserts made for gun work that don't 
leave a mark on the black plastic or soft aluminum of the T-17 variants.
73,
Mike

On 8/27/2014 11:13 PM, hwhall at compuserve.com wrote:
>> What are the dimensions of that element?
> The outside diameter of the pictured unit is 1.75 inches.
>
>   Wayne
>
>   
>
> -----Original Message-----
> From: Jim Haynes <jhhaynes at earthlink.net>
> To: hwhall <hwhall at compuserve.com>
> Cc: milsurplus <milsurplus at mailman.qth.net>; boatanchors <boatanchors at mailman.qth.net>
> Sent: Wed, Aug 27, 2014 8:29 pm
> Subject: Re: [Milsurplus] T-17 microphone
>
>
> What are the dimensions of that element?  Wonder if a modern telephone
> handset carbon mike element would fit in there.  (I know people used to
> substitute the old F1 telephone mike elements, but they were too big
> and had to be taped on to the front of the T-17.  Very non-authentic.
>
> A modern (for 1960) carbon mike element is the T-1 used in the Bell 500
> type phones, G-type handset.  I just measured one to be 1 3/4" in
> diameter at the rim, then the rim part is about 1/4" thick, then the
> total thickness is about half an inch.  Without a T-17 mike to look
> at I'm guessing that might fit inside.  Much easier than trying to take
> the original apart and replacing the carbon.  Also you can get an
> electret replacement for the telephone carbon transmitter.
>
> Now the T-17 mikes were remarkably insensitive even when new.  I don't
> have the facts, but it's my belief that was done intentionally so that
> the user had to yell into the mike to be heard over the engine noise
> in an airplane.  The T1 should be a lot more sensitive.
>
> Jim W6JVE
>
> jhhaynes at earthlink dot net
>
>   
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