Friday, April 15, 2011

Federal TV corp. AM-864/U audio compressor/limiter (Vintage circa 1954)

"The AM-864/U is a peak-limiting audio frequency amplifier for use in either AM or FM broadcast system installations where it can automatically control the maximum level of amplification while retaining the audio quality of the program source. The AM-864/U could also be used in recording or in sound systems where automatic level regulation was going to be a requirement. The input Z is 600 ohms balanced and the output is also 600 ohms Z balanced, which is normal for most broadcast audio routing. Five tubes are used in the circuit that is powered by 115vac. The rear chassis adjustments control the point at which limiting is started and also how much limiting is allowed. The large control on the front panel controls the amplifier gain. The panel switch on the left selects if the meter is going to monitor the attenuation level or the amplifier output. The AM-864/U is a high quality device that had multiple uses and apparently the U.S. Army did use them in many different applications. Dates from the mid-1950s."
The AM-864/U sounds amazing on kick, snare, bass, guitar and vocals. Recommend using an inline pad on the output as this unit has some serious output gain. 
Here's a link to the AM-864/U manual:

and a current ebay auction:

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