[Milsurplus] BC-344

[Bruce Gentry]

Bruce Gentry wrote:
> WA5CAB at cs.com wrote:
>> BC--314(*) was part of SCR-177-B.  I've always assumed that 
>> BC-344-(*) performed the similar function with SCR-188-A, although it 
>> isn't listed as such.  Either would have been used when the 
>> associated Radio Set was issued with any of the MF tuning units 
>> (except not with the TU-5).
>>
>> At the beginning of WW-II, the relatively new LS-3, LS-7 and HS-23 
>> were expected to be the standards for the next several years.  They 
>> are all either 7000 or 8000 ohm input units.  The output impedances 
>> of the newer receivers (BC-224, 312, 342 and 348) were all 4000 
>> ohms.  The idea was that from one to four of any mix of those audio 
>> loads would work with no more than a 2:1 mismatch.  When headsets and 
>> eventually loudspeakers went to 500 ohm, the output transformers were 
>> tapped at 250 ohms.  Same scenario as with the High-Z accessories.  
>> How/why 500 became 600 I don't know.  Typo on an order, maybe.
>>
>> In a message dated 8/29/2010 7:08:12 PM Central Daylight Time, 
>> telegrapher at q.com writes:  
>>> What system might have the 344D been associated with?  Since it's 
>>> powered by 120Vac, perhaps a tower environment tuned to one of the 
>>> A-G channels?  What speaker was associated with it.  Neither of my 
>>> Tm 11-850-N nor TM 11-850 address the issue as i can see.
>>>
>>> In the chart in front of TM 11-850 the 314 (12V) and 344D (120Vac) 
>>> are standalone units, not associated with anything in particular.  
>>> Must be more info out there someplace.   Why the 250 ohm 
>>> speaker/phones tap? 
>>> Larry
>>> W0OGH
>>>
>>>     
>>
>> Robert & Susan Downs - Houston
>> wa5cab dot com (Web Store)
>> MVPA 9480
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>>   
> I will guess the LF  BC-314/344 receivers were used for  aircraft  
> communications among others, because the ART-13 and BC-375 did 
> transmit on the LF band.  Usually, it was the other way around with 
> the aircraft transmitting on HF and listening on LF.  Also, LF was 
> used for long distance paths with very high power transmitters, a 
> reliable anytime anywhere signal by brute force. As for the 600 ohm 
> impedance, it was established by the telephone company and became the 
> standard for broadcast audio. There could have been a patent issue 
> preventing it from being used elsewhere, or a desire from 
> manufacturers to standardize. Just a few ideas.
>
>     Bruce Gentry KA2IVY
>