Beautiful early piece of history. Made by AMERICAN RADIO and RESEARCH CORPORATION. Serial no. 95. Measures 12” long and 8 1/2” high to the top of the Spark gap. Flat rate shipping in USA $25.

From AI google:

The Amrad Type C Spark Coil (also known historically as the Type C-1 Induction Coil) is a highly collectible piece of early wireless telegraphy hardware manufactured around 1917 to 1920 by the American Radio and Research Corporation (Amrad). Founded in 1915 in Medford Hillside, Massachusetts, Amrad initially specialized in producing maritime and military-grade wireless transmitters before shifting toward early amateur consumer radio gear.

Historical Context & Specifications

• Function: It functioned as a step-up induction coil designed to convert low-voltage DC power into a high-voltage electrical discharge across an adjustable spark gap, creating the electromagnetic waves required to transmit Morse code.

• Power Requirements: The Type C-1 coil was typically powered by a 6-Volt to 10-Volt DC storage battery.

• Design & Build: True to the "Marconi spark gap" era of the 1910s, it featured a rich mahogany wood base, a gloss-black Bakelite insulating bar, an integrated vibrator interrupter, and heavy adjustable spark-gap hardware mounted right on top of the coil.

• Historical Significance: Complete wireless transmitter setups using this specific coil often featured an integrated telegraph key, an antenna send/receive knife switch, and an ammeter to monitor current. At the time of its initial advertisement in publications like Popular Science in mid-1920, the unit originally retailed for $28.50 USD