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Scientific prototype 761 g

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  • Scientific prototype 761 g

    hey I found this thing in a dumpster today at a college. it is a Scientific Prototype Mfg. Audio threshhold detection relay 761 G. this thing was built with child psychologists in mind not engineers, I have no Schem. looks that it is a decent quality solid state preamp with the output set up to go to a printer. Click image for larger version

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    I have no idea what N.O., C. or, N.C. mean. any ideas on how i could just install a 1/4' jack (or more) as an output.

  • #2
    Very hard to say without a schem. My first reservation would be that most printers don't require current. Unless you mean to say that this thing was built to power some kind of mechanical printing machine. In which case we have no idea what kind of signal would come out of the back end. Or what the ideal load would be. You can bet it's nothing like a speaker load. Salvage whatever you can (big heat sinks are expensive) and put it back. Just one suggestion.
    "Take two placebos, works twice as well." Enzo

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A


    • #3
      NO = Normally Open
      NC = Normally Closed
      C = Common

      Refers to relay contacts. I assume the thing is a sound-operated switch. In the absence of sound, NC is connected to C. When a sound is detected, the NC contacts open and the NO ones close, so C ends up connected to NO.

      From a music electronics point of view, it's a nice 19" rack chassis and some knobs.
      "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"


      • #4
        Yes it is.
        It's a very crude, mechanical squelch add on, designed for military radios which lack it.
        I bet the military payed U$200000 for a two way radio that has less functionality than a $40 Motorola Walkabout.
        Juan Manuel Fahey


        • #5
          People who get research grants are often technical dummies (even PHD students). They'll write a piece of software and have no idea why it doesn't work. They spend outrageous money on relativly simple gadgets so they can do their research. I was involved in such a project. It was essentually a beeper and an LED that plugged into an RS232 port so the researchers could tell if their software was working. Price: $300 USD. The researchers didn't care, it wasn't their money. They just needed to get things working so they could collect data.

          Looks like a nice chassis. Just gut it and build your own preamp.
          WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
          REMEMBER: Everybody knows that smokin' ain't allowed in school !


          • #6
            Yeah i was kinda getting the idea of the sum of all the advice put forward here. after examining the device I will try two things and if neither work I will just gut it and do a build with the chassis. I will keep you updated. The first is just to bypass the relay and see what happens. I will let you know in a month or so how this goes.


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