[Milsurplus] T-17 Rebuild

[hwhall at compuserve.com]

Reaming the T-17 interior to accommodate telephone elements was considered undesirable at the WWII museum I volunteer for.  It turns out there are a few more modern telephone type carbon elements that are smaller than the nominal T-17 interior of 1.75 inch diameter.

Audiosears Corporation web site shows a number of vintage-style mike elements with links to additional spec data.  Part numbers 1277 and 1628 (aka N-1 type), look like possibilities.  N-1 elements were used in telephone switchboard boom-mike headsets like the Western Electric Model 52.  I got a few to try out.  Fitting the little N-1 element into the T-17 cavity requires fashioning a simple adapter.
A trial was also conducted using a T-100 type element obtained at a local surplus store (now gone).  The only maker’s mark on them was a logo with the letters NYC inside a diamond shape.  They're physically equivalent to the old standard T-1 element (like in your photos) and were manufactured until the 1980s by Nakoyo Telecommunications Inc.  An email to Nakoyo returned the information “T-100 is equivalent to USA T-1.”
A similar product is the 75555 element by ITT Kellogg (originally Kellogg Switchboard &Supply).  Both T-1 & 75555 are described by antique telephone buffs as very good carbon elements.
My experience was that the T-100 turned out to be a lot more sensitive than the N-1 type element.
The T-17 cavity originally had a plastic-like ring that isolated the sides of the element from the mike’s metal body.  In my experiment, to fit the T-100 parts, that ring had to be replaced with something thinner.  A slip of printer paper turned out about right.  I'm unsure that such an electrical isolation is always necessary.
If the telephone element seems to rattle a bit in the T-17, you can hold them snug with a large rubber O-ring.  When the mike cover is replaced it compresses the O-ring a bit and holds the parts firmly.
Maybe I should mention that a T-100 element could not be made to fit a Sonetronics brand M-15 microphone we had at the museum, even though the M-15’s body resembled the T-17 very closely.  The internal cavity was just slightly too small for even the stripped-down T-100 part.  I wonder if there were slight variations in the cavity size of T-17 brands as well, so that a T-100 may or may not be able to fit in a particular T-17 body without further modifications.
WayneWB4OGM

-----Original Message-----
From: B. Smith <smithab11 at comcast.net>
To: Milsurplus <milsurplus at mailman.qth.net>
Sent: Tue, Jul 19, 2022 10:25 am
Subject: [Milsurplus] T-17 Rebuild

         Several have asked about replacing the carbon microphone element  in the T-17. I usually use a standard telephone button and trim it to fit inside the T-17 housing by removing the outer frame. The button then fits inside the T-17 housing and the outer cover  with the small center holes can be fitted. (Drill additional center holes if necessary to improve voice response) Other have taken a T-17 housing and machined the interior  to  enlarge it to accommodate the larger button but removing the outer frame  with a small file is faster and easier.  There is no compassion between the audio output level between the original T-17 cartridge which has aged and the telephone button, the button  is loud and very crisp. See attached photo.
          Info on the T-17 including the button mod,capacitor info, rewiring etc can be found at  the link below. In addition there is a chart supplied by WA5CAB on the different  contract dates and manufacturers  of which  I've added a couple of entries. I will add additional info to the chart if I receive the information. 
 k4che
 http://k4che.com/T-17/T-17.htm
 
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