Mono In-Stereo Out boingy greatness from Germany in a rack, possibly related with the similar Vermona spring reverb unit.
Some pics:
My second hand unit has been repaired before (burned resistor..) 
This tells us the reverb tank is specced at IN 10 ohms OUT 2575 ohms 
Accutronics tank 
Driver circuit 
Input/output/ac in board 
Gutshots show this is a fairly simple unit, its driver circuit consisting of a few ics (TL072, LM380M, LM833N) some jumpers, low noise high precision resistors, OEM capacitors. Maybe its simplicity speaks for its quiet operation.
The reverb tank itself is a Fender Reverb amp compatible model, Accutronics model 9AB2C1B, medium delay (Length: 42,5cm. 3×2 springs, input impedance: 10 Ohm / DC: 0,8 Ohm, output impedance: 2575 Ohm / DC: 200 Ohm).
Masuto's 