AKG BX 15 Two Channel Spring Reverb Unit

AKG, which was primarily known for its microphones and headphones, began launching a series of spring reverbs in 1972 with the huge BX 20. This was followed by the BX-15 (probably 1973 or 1974), the BX-10 (1975) and the BX-5 (1980) as a rackmount configuration. 

Two mechanically and electrically separate and isolated channels make it possible to handle two independent signal sources with different decay times (1.5 - 3.5 seconds), treble and bass settings and reverb intensity.