Ortofon STL-631 mid-60s - Silver

This one was recently serviced and the power transformer was replaced. I have the original but the new one is an upgrade from the older one. Also, all of the tubes are Telefunken and in great working matched condition. The unit also has 4 matching transformers (Triad A-67J) on the inputs and outputs along with TRS 1/4" connectors for use in your studio or mastering room or with a cutting lathe. Comes in the rack as shown. These units are rare and this one is in excellent condition for its age with no known flaws.

Here is a description I found online which seems to cover this unit.

An automatic low-pass filter/acceleration limiter/treble overload protector/de-esser for disk cutting, radio broadcast and studio work. Simply put, this unit keeps the treble frequencies in check.

This is a rare piece of equipment

Designed and built in Copenhagen, Denmark, in 1963 this valve/tube-based 2U high, 19" wide rack-mount unit is built to the highest of standards. It was built for various pro audio applications, primarily 1) vinyl/acetate disk cutting systems (Ortofon, Neumann, Lyrec, Scully, etc.) and 2) radio broadcasts. It can, like its younger STL-731 cousin, also be used as an amazing and natural sounding - and extremely fast that is - de-esser (for e.g. vocals, drum overheads, synths, guitars, etc.) in modern music studio productions. Basically, it's two low-pass filters that automatically vary their cut-off frequencies according to the input level and the threshold level. Quote from the original manual: "two independent low-pass filters with the cut-off frequency continuously variable from 20 kcps to 7 kcps controlled by associated amplifiers with adjustable threshold and specially shaped frequency response."

It is a stereo unit with two meters (channel A and B; showing the cut-off frequencies), a shared COMMON LEVEL adjustable pot (left side of the unit), a bypass switch (red; center of the unit), and an on/off switch with associated red lamp and fuse (right side of the unit.

DETAILS:
Width: 19"
Height: 2 rack units
Weight:14 lbs./6,35 kg.
Power: 110-115/220-230 volts AC, 50-60 cps. Consumption 31,5 VA
Time constants: less than 05, milliseconds attack, 80 milliseconds release (non-variable)