BF256 JFet Pin Outs

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  • barry wilkins
    Senior Member
    • Aug 2009
    • 172
    #1

    BF256 JFet Pin Outs

    I have been making a small video amplifier ,when I look on the website some data sheets say pin 1 is the gate ,and others say its pin 3 .The source is still in the middle on pin 2.
    Do you think this correct ,or a mistake on the data sheet ?

    Barry Wilkins
    Tags: None
    • retiredcaps
      Badcaps Legend
      • Apr 2010
      • 9271
      #2
      Re: BF256 JFet Pin Outs

      I'm far from an expert on these chips, but two of the biggest reputable names, Motorola and Fairchild document gate as pin 1.

      If you have a breadboard, could you test to verify?



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        Comment

        • barry wilkins
          Senior Member
          • Aug 2009
          • 172
          #3
          Re: BF256 JFet Pin Outs

          Yes you are right ,I think it was the data sheet from On semiconductor that had different pin outs.
          Interestingly reversing the source and drain connections did not seem to make any difference to the results ?
          I am using BF244 jfets on my circuit at the moment as I have quite a few of these ,when I am happy with the circuit I will go back to the BF 256.
          Never thought a video amp would be difficult to make ! I keep losing the colour which is the HF component .
          Think I am going to use an LM318 IC after the BF 244 jFet ,this circuit is doing what I what ,inverting the video and allowing me to connect it to my video source without dragging in down ,just need to reduce the impedance to 75 ohms. I might try another emitter follower circuit or a source follower .

          Barry Wilkins

            Comment

            • PeteS in CA
              Badcaps Legend
              • Aug 2005
              • 3579
              • USA, Unsure of Planet
              #4
              Re: BF256 JFet Pin Outs

              The LM318 is a good op amp and has been around for a really long time. IIRC, its gain-bandwidth product is 100MHz. If that's adquate it could be a good choice. It's not exactly a low supply current part, though.
              PeteS in CA

              Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
              ****************************
              To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
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                Comment

                • barry wilkins
                  Senior Member
                  • Aug 2009
                  • 172
                  #5
                  Re: BF256 JFet Pin Outs

                  Thanks ,no real problem with the amount of current used by the LM318. Just drawn up more designs on multisim . I need to try them out in the next few days .One thing I do know is building the circuit on a breadboard has far too much stray and can cause the colour to disappear .The luminance is low frequency 7.8KHz and sub frequencies ,but the colour is 4.443MHz

                  Barry

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