Thunderbolt Siren Series
The Thunderbolt siren was a supercharged electromechanical siren produced by Federal Electric, which later became known as Federal Sign & Signal and Federal Signal. The Thunderbolt has seven chopper levels, or voltage settings, that allow the pitch to be adjusted on the chopper, the Thunderbolt can come in three port ratios, 5 Port, 4/5 Port, and 5/6 Port.
Thunderbolt 1000
The Thunderbolt 1000 is a single-tone siren. The 1000's chopper has 5 ports.
Thunderbolt 1000T
The Thunderbolt 1000T is a dual-toned siren. The 1000T can come in 4/5 or 5/6 port ratios, which correspond to minor 3rd and major 3rd intervals, respectively.
Thunderbolt 1003
The Thunderbolt 1003 uses two solenoids that are attached to the upper portion of the siren to create a third, high-low signal, which can be used as a fire signal. Otherwise, it is identical to the 1000T.
Other models
= Thunderbolt 2000
A single-tone variant from the 1950s with a gas-powered blower.