[ARC5] Headphones H-43 B/U

[Richard Knoppow]

----- Original Message ----- 
From: "Dennis Monticelli" <dennis.monticelli at gmail.com>
To: "Kenneth G Gordon" <kgordon2006 at frontier.com>
Cc: "ARC-5 Maillist" <ARC5 at mailman.qth.net>
Sent: Tuesday, March 25, 2014 6:56 PM
Subject: Re: [ARC5] Headphones H-43 B/U


> Ken,
>
> I am back from my business trips and can now report on my 
> measurements from
> a few years ago.  I too found a sealed and boxed H-43B/U 
> at a local flea
> market.  The mil seller must have had 30 of them.  I paid 
> $2.
>
> DCR = 4550 ohm
> AC impedance = 21K at 1KHz  (cans wired in series?)
> 1mV drive at 1KHz plainly audible.  That equates to 50 
> pico-watts!
> With proper impedance matching, these could be used in a 
> crystal set.
>
> Dennis AE6C

    Scott shows a couple of H-43B/U phones from different 
manufacturers at
http://oldheadphones.com/crystal/gallery/gallery2.html

    Most phones are connected in series.  These are probably 
a variation of the Western Electric type 509W. The DC 
resistance sounds a bit high but the impedance of magnetic 
phones is usually about 5 to 7 times the DC resistance so 
its probably correct.  These are at the high end of the 
impedance range. Phones like these were intended to work 
from high impedance sources such as crystal detectors and 
low level tube plates.  They are ideal for crystal sets 
except for the lack of fidelity. Most magnetic phones are 
resonant around 1 khz.  About the only phones with higher 
impedance are Brush crystal phones which have an impedance 
of around 100k. I challenge you to find a pair that 
works:-( I have maybe half a dozen individual Brush phones 
and only one capsule is not trash. FWIW, brush phones are 
connected in parallel so the wiring harness can't be used to 
replace the more common series type.
    Somewhere along the line I started collecting 
headphones, I have no idea why. I measured a number of them 
on a General Radio bridge. Impedance (not DC resistance) 
varies from around 50 ohms to around 25K ohms.  The military 
standardized on impedances of about 8K and about 500 ohms. 
The moving coils headphones for aircraft use ANBH-1 and 
ANBH-1A are 500 ohm (connected in series) and are quite high 
quality.  The ANBH-1A were military equivalent of the 
Permoflux commercial phones. The first stereo recordings I 
ever heard were played over a pair of split Permoflux 
phones. If these phones are in decent condition you got them 
at a steal.
   OK enough on something thats probably OT and a bore.


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