[ARC5] My mil phones - solved.

[Richard Knoppow]

----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: "Dennis Monticelli" <dennis.monticelli at gmail.com>
Cc: "ARC-5 List" <arc5 at mailman.qth.net>
Sent: Friday, January 02, 2015 6:00 PM
Subject: Re: [ARC5] My mil phones - solved.


On 2 Jan 2015 at 17:20, Dennis Monticelli wrote:

> They are probably HC -43B/U

     I think I may have a set of these but am not sure. If 
so mine were made by William Murdock, an old line company in 
Chelsea Mass. About the highest impedance magnetic phones 
are the Western Electric 509W and the Trimm Featherweight 
Specials at around 24 K. These measure about 2200 ohms DC 
but there were plenty of other phones with impedances of 
around 15K to 20K made for crystal detectors and similar 
applications.  The very highest impedance were the Brush 
crystal phones running around 100K per pair but these were 
connected in parallel instead of series.  These work very 
well on crystal sets and as bridge detectors. I have a pair 
of phones that came with my BC-221 frequency meter, not sure 
I ever measured them. They were also made by William Murdock 
Co. At the moment I am looking at a pair of Murdock phones 
marked "Headset Assy CCSP-49984-A
Receiver Type NT 49016A"   It seems to me that I discovered 
these were for a radiation detector but again I've lost my 
notes and don't remember. I also do not have a not of their 
impedance if I ever measured them but the DC resistance is 
about 1300 ohms.  They are similar in construction to the 
ANBH-1 with a small, completely enclosed mecanism and a cap 
that fits over the body.
    As far as sound quality, any magnetic headphone or 
others like the famous Baldwin phones which use a pin driven 
mica diaphragm, will be strongly resonant at some frequency, 
usually close to 1 Khz.  These do not sound good on speech 
or music. Moving coil phones, even when the response is 
somewhat restricted, are much better and have good 
inteligibility.
    Phones intended for use with radio receivers generally 
are around 600 ohms output where they are used on a 
loudspeaker output. Some military receivers have a phone 
output for higher impedance, around 5 to 10 K.  The 
Hammarlund Super-Pro series including the SP-600 have an 8 K 
ohm winding for phones which is loosely coupled so that even 
shorting it has little effect on the normal 600 ohm output. 
These will work with essentialy any impedance headphone.


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