[ARC5] LS-3 Speaker

[Roy Morgan]

On Mar 8, I wrote:
> Yesterdays hamfest netted an LS-3 speaker. ...  Does anyone know the input impedance…?

And I got a number of useful replies.  Here is a summary:

On Mar 8, 2015, at 4:06 PM, Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:

> According to Fair Radio Sales who sell those, there are basically two
> different kinds: 1) smooth finish, $58, 2) wrinkle finish, rusty, $49. They have
> opened one of each, and have found a transformer inside that has an 8K
> primary, and a 3.2 Ohm secondary, 270 to 3KHz, 1 watt.
> 
> Ken W7EKB

On Mar 8, 2015, at 5:08 PM, Meir WF2U <wf2u at ws19ops.com> wrote:

> The BC-348 is an airborne receiver. There were no speakers used on aircraft,... a BC-348 used by perhaps in a temporary ground control station may have been used with any speaker that was available if speaker operation was feasible in a given environment. The LS-3 speaker was used officially with the BC-312 and BC-342 which are ground equipment.
> 
> 73, Meir WF2U
> Landrum, SC

On Mar 8, 2015, at 5:49 PM, WA5CAB at cs.com wrote:

> Roy,
> 
> Input impedance is 8000 ohms.  Intended for use on the 4000 ohm outpput vehicular radios of the period, Mainly BC-312 family and BC-652.  The only documented usage of it with a BC-348 that I have found is with AN/MRC-20 (c/o AN/ARC-8, -3, & -27).  AN/VRC-1X, if any were assembled, might be a second example.  Ad hoc setups of SCR-287 at forward airports would have probably used one.  Ones produced during the Korean War were painted black semi-gloss.  A few years ago, I had 1246 of them, various variants.
> 
> I have never come across any paper on the LS-3.  It was later renomenclatured LS-215/U and 4000 and 600 ohm taps were added to the transformer.(and it was painted green). 
> Robert Downs - Houston

On Mar 9, 2015, at 7:18 AM, DSP3 <jeepp at comcast.net> wrote:

> Meir is absolutely correct.  In many Signal Corps photos, those taken at AAF, and after 1947 at USAF installations, you'll see desk-mounted BC-348 receivers with an LS-3 speaker. One might be inclined to say that the LS-3 was the de facto, but un-designated ground-based speaker for the BC-348 for the reasons Meir points out.
> 
> Jeep - K3HVG


On Mar 9, 2015, at 9:40 AM, Scott Johnson <scottjohnson1 at cox.net> wrote:

> That is probably because the LS-3 was ubiquitous in the USAF from the late
> forties through the eighties!  I ordered one for a bench mockup in 1985, and
> it was of new manufacture!
> 
> Scott W7SVJ

On Mar 9, 2015, at 11:37 AM, Joe Connor via ARC5 <arc5 at mailman.qth.net> wrote:

> And let's not forget that the LS-3 just looks right alongside of or on top of a BC-342 or BC-348.
> Joe Connor 

On Mar 9, 2015, at 5:32 PM, billriches <bill.riches at verizon.net> wrote:

> I have made photocopies of a clean LS-3 label on thick photo paper if anyone is interested contact me off list.
> ...
> Bill, WA2DVU
> Cape May

I got the thing onto the bench tonight and made some measurements of the input impedance with a series resistor and voltmeter.  At 1000 cycles I get 8500 ohms and at 400 cycles, I get 7900 ohms.  During these tests I was feeding the thing about 100 milliwatts and was getting lots of volume.  

The transformer in this one is about the size of a 5 watt audio output transformer I have, so I would think the 1 watt rating mentioned above is conservative.

Thanks to all who contributed to the lore on these speakers.  My advice to anyone who has a chance to buy one:  Do it!

Roy


Roy Morgan
k1lky68 at gmail.com
K1LKY Since 1958