The AM Forum

I have   an old spark coil, rather large, (10"X5"X5" approx), in a large wooden box. 
Research shows that this coil was probably made by the Electro Importing Company.
I'd love to know how this coil was hooked up to make a  spark transmitter. 
Some pics attached.

Ed,
I have a coil that looks just like that but is a more modern version, probably used in a science lab.

I just applied 12v to the terminals on the end (maybe 6v for yours) and made a spark gap out of coat hanger and attached it to the terms on top. When DC is applied the vibrator or interrupter on the end buzzes and a nice spark is produced from the top terms (secondary). I keyed the DC off and on with an old telegraph key....it was fun until I got bored with the project.

PS - you could add a small tank circuit to the output if you wanted to simulate an old spark xmtr.

Looks like a Model-T spark coil.

A Tesla Spinner. Great for fishing. Get your limit every time.  ;D I prefer DuPont Lures myself.

I tried out a model-T ford spark coil once, added a tank circuit and coupled it to my antenna.  A local ham told me I was coming in loud and clear about 6 miles away.

Connect the battery to the primary side, and insert the key in the circuit.  Ground one side of the secondary side, and place the spark gap across the coil.  You can find circuits in early radio handbooks showing how to connect the output to an antenna, both with a tank circuit and without.

If you can't find an old radio book dating back to the spark era, look at the circuitry for a Tesla coil. There are probably ample circuits posted on the Net.  Just do a Google search. Tesla coils and spark transmitters are practically identical, except that with the Tesla coil, the resonant circuit remains unloaded, to produce as much voltage and corona as possible.  With the transmitter, the coil is made to  resonate at the desired frequency, and the antenna is coupled to the coil just like it would be from a conventional transmitter tank circuit.

GIYF. A search for '"wireless telegraphy" condenser spark coil' produced 1,700 hits, including these URL's:

http://www.hammondmuseumofradio.org/spark.html (http://www.hammondmuseumofradio.org/spark.html)

http://earlyradiohistory.us/1905mur.htm (http://earlyradiohistory.us/1905mur.htm)

http://www.1911encyclopedia.org/Induction_Coil (http://www.1911encyclopedia.org/Induction_Coil)

http://books.google.com/books?id=djONuFlc5lkC&pg=PA538&lpg=PA538&dq=%22wireless+telegraphy%22+condenser+spark+coil&source=web&ots=iWGi6u_N0T&sig=6kpQR9essrR1RzrAXomZhJKb15I&hl=en&sa=X&oi=book_result&resnum=10&ct=result (http://books.google.com/books?id=djONuFlc5lkC&pg=PA538&lpg=PA538&dq=%22wireless+telegraphy%22+condenser+spark+coil&source=web&ots=iWGi6u_N0T&sig=6kpQR9essrR1RzrAXomZhJKb15I&hl=en&sa=X&oi=book_result&resnum=10&ct=result)

http://earlyradiohistory.us/1902cons.htm (http://earlyradiohistory.us/1902cons.htm)

http://chestofbooks.com/crafts/electricity/Electricity-For-Boys/Chapter-XI-Wireless-Telegraphy.html (http://chestofbooks.com/crafts/electricity/Electricity-For-Boys/Chapter-XI-Wireless-Telegraphy.html)

http://chestofbooks.com/crafts/popular-mechanics/Amateur-Work-1/How-Wireless-Telegraphy-Apparatus-is-Made-and-Operated-I-T.html (http://chestofbooks.com/crafts/popular-mechanics/Amateur-Work-1/How-Wireless-Telegraphy-Apparatus-is-Made-and-Operated-I-T.html)

http://books.google.com/books?id=R41IAAAAMAAJ&pg=PA3&lpg=PA3&dq=%22wireless+telegraphy%22+condenser+spark+coil&source=web&ots=XfjImUh-xO&sig=uOoweYsrAGYYe1w-9HMCDZr6o0s&hl=en&sa=X&oi=book_result&resnum=7&ct=result#PPA11,M1 (http://books.google.com/books?id=R41IAAAAMAAJ&pg=PA3&lpg=PA3&dq=%22wireless+telegraphy%22+condenser+spark+coil&source=web&ots=XfjImUh-xO&sig=uOoweYsrAGYYe1w-9HMCDZr6o0s&hl=en&sa=X&oi=book_result&resnum=7&ct=result#PPA11,M1)

http://books.google.com/books?id=rOAOAAAAYAAJ&pg=PA33&lpg=PA33&dq=%22wireless+telegraphy%22+condenser+spark+coil&source=web&ots=HX75eFZO-n&sig=eRXl6Q3GFZ7761n3Ctp_eLiNQRM&hl=en&sa=X&oi=book_result&resnum=8&ct=result#PPA35,M1 (http://books.google.com/books?id=rOAOAAAAYAAJ&pg=PA33&lpg=PA33&dq=%22wireless+telegraphy%22+condenser+spark+coil&source=web&ots=HX75eFZO-n&sig=eRXl6Q3GFZ7761n3Ctp_eLiNQRM&hl=en&sa=X&oi=book_result&resnum=8&ct=result#PPA35,M1)

HTH.

73,

Bill W1AC

The replies here are excellent, (thanks Don), and are very helpful.  My goal now is to try and find various components, such as the "oscillation transformer", or "helix" coil,   a vintage type spark gap and a suitable condenser, but I think I can use one of my broadcast micas for that.  The intention is to set up a suitable spark display station in the shack for my amusement, and the amusement of guests.  Hooking up an antenna will be "optional", of course!  ;D :P

Hey Ed, thanks for bringing up this topic, I have the exact same spark coil, it
didn't have any manufacturing labels on it, so I was thinking it was homebrew.
Anyway doing a search on Electro Importing Company, I found picture of it
set up  as a spark transmitter..
http://earlyradiohistory.us/1910ei.htm (http://earlyradiohistory.us/1910ei.htm)

Hi Ed, looks like the fellows handled your request pretty well.

I do have a spark transmitter, homebrewed, that works with that type of coil.

I can send over some photos if you can take larger files.
It is nothing fancy, just some wood, copper tubing, and a set of spark gap points.
The original builder wired up a tuning circuit with caps and a large inductor to roughly set the freq,
but it does not do much, when the rig is operating, it is several dozen KC wide.
Don't ask me how I know.  ;)

I'd try your coil on 6 volts first, mine will arc nearly 1" on a 6 volt lantern battery.
You'll find that the point cap on the contact will need to be adjusted after some extended use.
If the gap gets too large, the electromagnet can not pull down the arm and break the circuit.
By the way, mine is not made by the Electro Importing Company, Gernsback's old biz, but rather but another firm.
Still, they all seem to employ roughly the same design.

What about the coherer?

Metal filing or mercury?

I'm fresh out of tappers, so you might want to choose mercury.

Nah.... we're a sending station only!   :P

Actually, a receiving "set" might actually be more of a challenge, in that  I'd need  some kind of simple, 1920's style receiver.   Regen?   Crystal?     A coherer might be a real challenge.

I think I'll deal with the challenges of building a  spark sending set first.

Thanks for that link, it was very useful.

Excellent, Bruce.  Yes, please send me the photos.  I believe my email address is clickable.    Interesting.  It would be useful to  set the frequency, rather than just send  blind.   

Mercury for sure. What kinda station would you have without some toxic materials in it.

Then you can construction some slop jar rectifiers.