ALTEC 9073A Graphic EQ plus Fairchild 661TL

Two hard to find pieces in a vintage 60's rackmount package. No Longer available.
Fabrikanten:: Altec , Fairchild
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A unique custom panel with an Altec 9073 6 Band Passive Graphic EQ and a Fairchild 661TL Auto-Ten automatic attenuator.   This combination was put together for a small local film processing studio.    Both pieces are in good condition and are mounted onto a heavy duty flanged 4 RU (7") plate.  

The Fairchild Limiter has a small 6.3 volt filament transformer wired to a neon lit push-push power switch.   We guarantee it is not UL approved, so use it at your own risk.   The Fairchild was marketed as an alternative to limiters of the day as a means to avoid any changes in the Dynamic range of program material. 

Here are some of the highlights from Fairchild's literature:

The FAIRCHILD AUTO-TEN uses an exclusive FAIR­CHILD sensing cell and sensing amplifier.   The AUTO­ TEN automatically and rapidly provides attenuation from 3 db to 60 db.

The AUTO-TEN is an automatic attenuator designed to reject unwanted signal or noise. It is made pos­sible by the use of today's solid state technology .
The AUTO-TEN should not be confused with limiters or compressors, or other devices that change dynamic range, for the AUTO-TEN does not change, or squeeze or alter the dynamic range of program material. Per­haps the easiest way to think of the AUTO-TEN is to think of it as an on-off switch with a brain. There have been voice-operated relays, but they did not possess real discretion. The AUTO-TEN has discre­tion through the use of a transistor amplifier and the FAIRCHILD solid state sensing cell, and a variable release time.
The sensing cell is actuated by a transistorized sensing amplifier . The amplifier continually senses the audio signal of the channel in which the AUTO­ TEN is placed. The sensing amp lifier has two con­trols: a threshold and a release time . A threshol d is selected by the operator, then when the signal falls below the present threshold, infornation is attenuated up to 60 db. The release time control allows a varia­tion from 300 milliseconds to 7 seconds. Release time governs the amount of time needed for complete at­tenuation. This permits slow or rapid attenuation as dictated by the program material and the production effect desired .

  • Economic Noise reduction in tape and film recording
  • minimize 'breathing' in  compressors and limiters
  • Minimize noise in multi-track tape playback
  • Improve gain in PA systems

Fairchild 661 Specifications: 

  • Input Impedance: 150 ohms to 47,000 ohms
  • Output Impedance 150 ohms to 47,000 ohms
  • Insertion Loss:    2 db at 150 ohms,  .5 db a t 600 ohms
  • Frequency Response:   Flat (resistive network)
  • Distortion:  NONE
  • Power Requirements:  6.3 V AC 60 or 50 cycles  at 200 ma 8 V DC at 200 ma
  • Input Level Requirements:   - 35dbm or higher, no higher than +256dbm

The Altec 9073 is an great example of how much things have changed when it comes to materials and build quality.  The EQ modules appear to be the same as the ones used in the Altec model 9062A.

Here are a few details on this Altec Passive EQ:

  • Gold traces throughout, wider and thicker than current standards
  • Gold eyelets in all PCBs
  • PCBs are glass epoxy, not phenolic
  • .25" thick Aluminum side and front plates
  • Pivoting Wiper arm with redundant gold spring contacts
  • Mylar caps throughout
  • Air core coils throughout

The Atlec 9073A is a passive EQ with center frequencies at:

  • 64 HZ
  • 160 HZ
  • 400 HZ
  • 1 KHZ
  • 2.5 KHZ
  • 6.3 KHZ

It provides a center detent with a range of +8  db at each frequency.

Additional information on this piece is scarce and some of the sources may be unverified.   With that in mind here is a selection of comments we've found in our searches. 

 The Altec 9062A and Langevin 252A are both bridged-T constant impedance passive circuits. I've attached a diagram of the basic Constant-B implementation (see H. R. Kimball's "Motion Picture Sound Engineering" from 1938). X1 and X2 are the reactive elements—series and parallel LC pairs (inductors and capacitors).  For a single band of boost and cut, you need a 4 pole 17 step (±8db in 1db steps plus flat) switch for the eq steps, plus additional switching to flip the LC pairs between boost and cut mode (Solomon and Broneer's Constant-S version cut down the attenuators needed from 4 to 3). This is a massive (expensive) and complex switch.   See the picture of the guts of a single band from my Altec 9062A to get an idea of what's involved—the pcb/wiper construction was also how Altec/Langevin built their step attenuator faders and pan pot sliders. In both Altec and Langevin products from this era, the boards are etched glass epoxy with gold plated traces. The wipers are bifurcated (redundant contacts). I have never seen one of these boards with corroded traces.

The 6-band Altec was designated for "motion picture recording and dialogue" while the 7-band (was) for "music recording." The frequency bands of the 9073 are almost identical to the Cinema Engineering 7080 despite differences in implementation: 64, 160, 400, 1000, 2500, 6300hz. The only discrepancy is the Cinema's first band, which is 63hz.