Vintage Federal AM-864 limiting compressor tube amplifier limiter.Signal Corp Amplifier. Originally intended for use by the U.S. Army. Here's a very early 50's (serial #58)  nice working Federal AM-864 Amp. The limiting quality and overall frequency response, particularly the low end, sounds excellent on it.  Sounds great on bass, ambient drums, guitars, anything actually.  The unit has a lot of overall output gain.   It's a well built tube and transformer based push pull circuit with a pair of 6SK7 as the control amplifier and a 6SN7 as the output.  A 6SQ7 acts as both a modulation signal amp as well as providing negative dc control bias.Very simple and effective rackmountable compressor amp.  This one's in nice workng shape, cosmetically a bit of paint wear here, the odd scratch or scuff here and there and pitting and blemishiness from over 60 years age, looks cool in its own way, but not mint. The inside on the otherhand is tropicalized and very clean. Regardless of the cosmestic blemishes, it's a great overall specimen, and works nicely.  The main audio coupling caps that were the 60 year old mica caps were replaced with Wima Poly's and Sprague 716.The change of audio coupling caps much improved the overall clarity and fidelity of this unit.  The main electrolytic filter cap is a newer but very similar cannistor type model with a bit of extra capacitance added.It runs pretty quiet for a 60 plus year old tube amplifier. The AC cord has been substituted with a soldered in newer unit with a chassis safety ground, not the prettiest, but it's functional and adds a safety ground. Check the photos for details. Schematic is fastened onto the inside of the chassis for convenience. The unit has added pigtailed XLR in and outs. They're presently hooked up as unbalanced, but sound fine running off balanced or unbalanced sources.   There's lots of info. about these online.  One minor technical issue, common to these, but not affecting the sound, is the meter in Gain Reduction mode sits in resting position  a bit beyond the normal 0 db point, but once the audio kicks in, it quickly starts to dance downward effectively registering the gain reduction occurring.  The meter can also be set to display output volume.  Being over 60 years old, there are no guarantees or returns due to age, so it's sold as is,. but this is working well in good condition as I describe here and tested just before writing up this ad and very functional and usable.  I'll pack it well to survive shipping. These are pretty rugged units, so bid with confidence..  Check my feedback. I will ship worldwide with some some exceptions.  Paypal only.