[ARC5] Carbon Microphone Inquiry

[hwhall at compuserve.com]

 I was recently working on a T-17 restoration and couldn't resurrect the original carbon element. Some smaller N-1 type elements were donated and they seem to work fine. They are smaller than the original element (~1.3 inch diameter vs original 1.75 inch dia) so a filler/adapter ring is needed and you have to solder the T-17 leads onto it. 

The T-1 types are just a hair too large to fit the T-17 handle but I've been playing with a T-1000 (same size as T-1) that looks like it would fit after l pried off the tin outer crimp ring that holds it all together. It separates to three parts: a perforated cover plate with 8 holes, a thin black plastic sheet or film, and a cone shaped metal diaphragm assembly that contains the carbon grains. The grains are sealed in the latter and won't come out unless you rip the metal diaphragm out. By the way, you have to solder to these types, too.

With the outer crimp ring removed the diameter was a few thousandths less than 1.75 inches. If supergluing the outer edges of diaphragm etc together were to prove strong enough to hold the parts together, this surgery may work for T-17 element replacements. But the thin black plastic film behind the 8-hole grid may not take glue well.

It may also be workable to just drop the three parts into the T-17 element cavity along with a spacer ring that will compress their edges together when the T-17's cover plate is screwed down. Something to experiment with!

 

Wayne
WB4OGM

 

-----Original Message-----
From: k7mks <k7mks at comcast.net>
To: arc5 <arc5 at mailman.qth.net>
Sent: Wed, Oct 15, 2014 11:00 am
Subject: [ARC5] Carbon Microphone Inquiry


Am restoring a Stancor ST-203A 10 meter rig which requires a carbon microphone 
into a 6J5 grounded grid speech amp to a pair of 6V6's.. Would appreciate 
comments from those who have experience with the the T-17 and Telephonics mics. 
Does one have advantages over the other or it it a push? 

I trust this inquiry about carbon mics will be appropriate for group. 

Thanks joe k7mks 

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