[ARC5] Re: Fw: [Milsurplus] $400+ for a T-17???

[Mike Hanz]

All carbon mikes are problematical from the compaction problem.  If not 
badly compacted and frozen in time, all they really need is more gain.  
If you are using an interphone amplifier as a part of your military set, 
a simple wiring change may be all that is needed.  Steve Williams made 
such a minor change to a 274N set with a BC-347 interphone system that 
was showcased at the Collins Radio Club event a year or so ago 
(http://www.collinsclubs.com/carc/b-29/ ), and had plenty of drive for 
the BC-456 modulator as a result.  The small circuit change of the jack 
box (station box) is at the bottom of 
http://aafradio.org/docs/RC-36.html but similar results can be obtained 
with a variety of other amplifiers.  For example, there was a series of  
preamps made for the purpose of using British dynamic mikes in US 
aircraft, beginning with the BC-216 in the late 1930s.  They do very 
well with a properly conditioned T-17 (all carbon mikes need a bias 
voltage to allow current variations to be reflected as voltage 
variations on the amplifier input.)  Although I hesitate to mention it, 
there are probably tiny Radio Shack preamps that would do the same job 
in a pinch... :-)

 - Mike

Ray Fantini wrote:

>I have a couple T-17 that I changed the element and also installed new
>covers on using parts from TA-43 telephones. would think about the only
>way to get good audio drive from a stock T-17 is by yelling in it. so
>dose this mean I destroyed $800 worth of microphones?, see that their
>are still three other T-17 on ebay with no bids, maybe that's a T-17 for
>your "Collins" radio.
>