At the time of the introduction of FM stereo in Europe, the pre-war and early post WWII audio compressors like the U13, U17 and U23 didn't hold up to the audio requirements of the Institute for Broadcast Technology, due to the fact they were designed for AM.

Development started at the "Betriebstechnik" of the NWDR radio station in Hamburg, and after three years the U73 in its earliest form was introduced; a three stage push/push variable mu design based on the chassis of the V76 mic pre, sharing about 50% of the same components.

This early U73 was built in a compact design comprised of a two Danner cassette module with a built-in power supply and a theoretic compression ratio of 100 to 1.

It was the fastest tube compressor ever built due to its forward triggered sidechain -for its time a mile-stone in audio technology.

The design was licensed to the historic TAB company in Germany who continued to build it for nearly three decades in several different versions, until finally discontinuing it in1980.

Due to its high price and fixed set up, the U73 only found its way outside Germany in one specific application; as a final mastering compressor for disc cutting laths, mostly in conjunction with an automatic release trigger; the Varicom.

Nearly every record recorded and cut in Europe from 1960 to 1975 was done with a stereo pair of U73s.

Today nearly 25 years after the production stopped in Germany, AMI is happy to reintroduce the next generation U73s with all the features needed in a modern recording environment.

These U73s are built on the same chassis we use for the new V76 as a one RU 19 inch mono version, driven by NOS made in Germany with TFK and Valvo tubes to insure the same great tonal quality that made the historic compressors world famous.