[Milsurplus] Morale Audio on Ships

[Bruce Gentry]

J. Forster wrote:
> Hi Nick,
>
> Thanks very much.
>
> The diagram I have uses a single-ended amplifier with a 117N7 tube, line
> operated (no power transformer). It does have the notation RDO on the
> print.
>
> What is very useful is to know the characteristics of the audio bus (6 mW
> @ 600 Ohms).
>
> I'd presume that each amp has a fairly high bridging input impedance
> (>20KOhm maybe ???)so that bus loading would not be an issue? Anybody
> know, please?
>
> Best,
>
> -John
>
> =================
>
>
>
>   
>> Spoke too soon - here is a photo and info on NT-49545
>> http://www.hnsa.org/doc/ecat/cat-1327.htm
>>
>> and the  NT-49620 (8"speaker)
>> http://www.hnsa.org/doc/ecat/cat-1330.htm
>> and it's predecessor  NT-49131 (5" speaker)
>> http://www.hnsa.org/doc/ecat/cat-1325.htm
>>
>> Aha! - I thought I had been imaging things as my 49620 is quite a bit
>> larger than a unit I had seen shipboard.
>>
>> Nick
>>
>> On Thu, Jan 13, 2011 at 2:29 PM, Nick England <navy.radio at gmail.com>
>> wrote:
>>     
>>> Hi John -
>>> Look at the NT-49620 selector/amp/speaker here (toward bottom of page).
>>> http://www.navy-radio.com/rcvr-spkr.htm
>>>
>>> There is also the NT-49545 selector/amp/speaker but I don't have any
>>> photos - just a drawing-
>>> http://www.navy-radio.com/navpers/3-58.jpg and this description
>>> Amplifier-Speaker Unit NT-49545
>>>    The Navy type 49545 amplifier-speaker unit, seen in figure 3-58,
>>> is a combination audio amplifier and loudspeaker assembly. Its
>>> reproduction qualities are considered good. Aboard most ships, it is
>>> installed in berthing and messing compartments as an entertainment
>>> loudspeaker.
>>>    All operating controls of the unit are located on the front panel.
>>> They consist of a power on-off switch, a power-on indicating lamp, a
>>> tone control, a volume control, and a channel selector switch that
>>> permits selection of up to five different entertainment (or
>>> communication) channels.
>>> cheers,
>>> Nick
>>> www.navy-radio.com
>>>
>>> On Thu, Jan 13, 2011 at 2:04 PM, J. Forster <jfor at quik.com> wrote:
>>>       
>>>> Hi,
>>>>
>>>> Does anybody have any info on the distribution of Morale audio to
>>>> Officer's compartments on WW II ships.
>>>>
>>>> Apparently thyere wasw one (or several) line level audio busses and
>>>> each
>>>> space had a selector switch, volume control, small line powered amp (1
>>>> tube, 117N7), and speaker.
>>>>
>>>> Does anybody actually have an amp (or manual for it) that could be
>>>> duped,
>>>> or info on how the audio signal was distributed. Was there a
>>>> distribution
>>>> amp also?
>>>>
>>>> Best,
>>>>
>>>> -John
>>>>
>>>>         
>>     
>
>
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>   
I have a restored Scott SLRM, and it has a winding on the output 
transformer for 600 ohm line output. Considering there are two 25l6 
tubes in push-pull, the output level is probably fairly good when the 
volume is set for a pleasing level from the built in loudspeaker. About 
3 volts of signal on the grid of a 117N7 in a typical circuit should 
give very satisfying volume. Many kiddie phonographs used that tube and 
drove it directly from a crystal cartridge without a preamp stage. A 
transformer wound for 10 or 20 K.  bridging and a 50k secondary should 
be able to deliver  plenty drive for the room amplifiers. Bruce Gentry 
KA2IVY