Inside the box are a pair of rare NOS dual-spring reverb mechanisms (four springs total, each with separate input and output transducers) manufactured by Baldwin in the late 60's for use in electronic organs. Each pair is wired in a humbucking configuration, and surrounded by appropriate impedance matching circuitry.
The unique tapered spring design creates a delay line in which the delay time is inversely proportional to frequency; the high frequencies propagate faster through the spring than the lows. The result is a smooth reverb with a remarkable degree of diffusion.
Mechanically, the two reverb mechanisms float inside the box, surrounded by a layer of resilient foam rubber padding.
Electrically, the inputs and outputs are completely isolated from each other. The inputs share a common chassis ground; the output grounds are isolated from the chassis ground and from each other. There is no possibility of ground loops.
Logically, this arrangement is like a reverb chamber; the outputs can be thought of as coming from a pair of microphones inside the box.