[GreenKeys] Western Electric Model 15B Main Line Telegraph Sounder, 1875-1900

[ad7i]

30 Ohms seems a bit unusual.  Most mainline sounders are 100 to 150 ohms.
Local sounders are usually 4 ohms, with a relay in the mainline and the
relay contacts driving the 4 ohm sounder via a local battery (around 1.5V).

I'm going to go out on a limb and suggest that 30 ohms might be used for a
large building intercom wire.  Longer loop than just the three feet needed
to connect a 4 ohm sounder to relay contacts and a local battery, but
probably not more than 2000 ft of loop wire connecting two to four sounders
within a big building.  I've been told that for 100 mile loops using open
wire along a RR right of way it was common to have 48 or 130V DC sources at
each end of the wire (positive at one end, negative at the other,
incandescent bulbs in series at each end to limit current if the line
shorts to ground) and use  earth ground to complete the loop.  Lots of good
wireline telegraph info in the "AT&T Green Book" (PDFs available on the
internet).

But you can find the people who really know their stuff about landline
telegraphy at   MorseLandlineTelegraphy at groups.io  rather than relying on
my fourth hand information.

73, Paul, ad7i
Middletown, NJ



On Thu, Nov 9, 2023 at 9:15 PM Roy Morgan <k1lky68 at gmail.com> wrote:

> I have one of these:
> Mainline Sounder 15B
> Marked "30 Ohms"
>
> I have read that often these were run by a local battery switched by a
> "sensitive relay" in the main telegraph line.
>
> It seems like this 30-ohm coil would be in series with the main telegraph
> line, and coils of higher resistance would be used with a local battery and
> relay in the line.
>
> Anyone have more information!
>
> (Asking prices for these seem to range from $80 to $130! This one is not
> collector quality but with work would clean up nicely.)
>
> Thanks.
> Roy
>
>
> https://www.thehenryford.org/collections-and-research/digital-collections/artifact/388676#slide=gs-300550
>
>
> Roy Morgan
> K1LKY Western Mass
> K1LKY68 at gmail.com
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