[ARC5] HS-33

[Richard Knoppow]

    The ANBH-1A (Army, Navy, British, Headphone) was designed to 
have high articulation of speech in aircraft. The design 
originated at the Harvard University laboratories. The receivers 
are low impedance moving coil types. Some have Bakelized cloth 
diaphragms and some have metal diaphragms. The phones were made 
by several suppliers. Permoflux made a commercial version 
offering a standard and high fidelity version, I suspect they are 
the same but the hi-fi ones may have been selected. Basic element 
has a voice coil impedance of about 20 ohms, the military version 
has a built in transformer to make it 300 ohms. This is for 
single units, usually they are supplied in pairs with the two in 
series so the impedance is either 50 ohms or 600 ohms. Higher 
impedance is gotten by an external transformer. There were a 
number of previous designs. The original magnetic type just was 
not clear enough under high noise conditions. None of the 
magnetic phones were good enough. Another type of similar 
headphone has a small diaphragm, I think they might also be 
magnetic but I've never disassembled one. These are the ANBH-1 
(not A) version. Same impedances. They do not have the wide 
frequency range of the A but are pretty flat in response. Most 
magnetic headphones are quite strongly resonant typically at 
around 1Khz. Work fine for CW but not for voice. In fact, the 
flat response phones may be better even for CW because noise 
doesn't make them "ring".
     Some of these came on headbands, at least two types, some 
came in pairs with a short cable for use in pilots helmets or 
perhaps for use in tanks. Aircraft and tanks have similar ambient 
noise problems.
     A similar headphone to the ANBH-1A is made for audiology by 
Telephonics.
On 8/9/2019 12:33 PM, Kenneth G. Gordon wrote:
> On 9 Aug 2019 at 18:36, D C _Mac_ Macdonald wrote:
> 
>> Receivers are Utah ANB-H-1.
> 
> As I understand it, if you have the ANB-H1 receivers, it is an HS-33.
> 
> Doesn't really matter in practical terms for most mil radios, but I prefer the older HS-23 types
> with their higher impedance.
> 
> However, the only set I have has one intermittant receiver. Gotta fix that some day.
> 
> Ken W7EKB
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL