The 550A EQ, one of his most famous innovations, was first released in 1971.

Hand-built and hand-wired, there will only be 50 units available.

The features, according to API, include:

• Hand-wired Limited Edition model with 50th Anniversary Faceplate
• Reproduction of the legendary 1971 550A
• 3 bands of classic API equalization
• 5 selectable frequency centers on each band
• High and Low bands offer shelf/peak switching
• "Proportional Q" narrows filter Q at extremes
• Switchable band pass filter
• Individually Serialized (1-50)