Do you know the name of this single-transistor oscillator?

Discussion in 'General Electronics Chat' started by Mark Hughes, Jul 19, 2016.

  1. Mark Hughes

    Thread Starter Member

    Jun 14, 2016
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    Hello everyone,
    Does anybody out there happen to know if this circuit has a proper name? It almost looks like a Colpitts Oscillator. Any help would be great.
    Thanks,
    Mark

    AudibleCircuitProbeSchematic_Mark Hughes.jpg
     
  2. DickCappels

    Moderator

    Aug 21, 2008
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    It is a blocking oscillator
     
    Aleph(0) and Mark Hughes like this.
  3. Mark Hughes

    Thread Starter Member

    Jun 14, 2016
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  4. Jeremy Lee

    New Member

    Jul 2, 2016
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    Sorry to muddle the issue - I'd have guessed it's a Hartley ( https://en.wikipedia.org/wiki/Hartley_oscillator ) because of the center tap? I recognize it being a common circuit in the RadioShack "101 Projects Kit", but I never knew the name. It's a beep/tone generator, yes?
     
  5. Mark Hughes

    Thread Starter Member

    Jun 14, 2016
    97
    6
    Hi @Jeremy Lee ,
    Thanks for joining the discussion. I'm inclined to believe @DickCappels got it right the first time. These pictures are taken by attaching probes across the speaker connections. The blocking oscillator has a metal-core inductor, whereas the Hartleys seem to have air-core inductors, giving the blocking circuit an extremely high L:C ratio.
    You're right, it is a beep/tone generator audio circuit. Do you happen to have a copy of your RadioShack "101 Projects Kit" with the circuit pictured you could scan or photograph and send me? I know I've seen it before somewhere too, but couldn't find it by flipping through my reference books, and don't have the Radioshack one. And it's one of those things that takes forever to find, but seconds to confirm.
    [​IMG]
    [​IMG]
     
  6. Jeremy Lee

    New Member

    Jul 2, 2016
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    Nope, haven't had that for 20 years. But I still remember wiring it up on the audio transformer in the top right corner with those little spring connector things. It's was the output stage of a lot of the audio projects - organ, siren, etc. ahh... here it is... The "200 in 1 electronic project lab"

    http://s395.photobucket.com/user/SeeMikesPics/media/200_1_Electronic04.jpg.html

    Ha! You're in luck. i think Tandy have put the manual online. That's cool, since this kit predated the internet by a decade, at least.
    http://www.tandyonline.co.uk/doc/28/28-249_User_Manual.pdf

    .. well, I hope it's the manual. It's taking forever to download... i'll post this for now, and if they manual turns out to be crap, I'll keep looking.
     
  7. Mark Hughes

    Thread Starter Member

    Jun 14, 2016
    97
    6
    Thank you sir. I too am waiting for it to download.
     
  8. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    While those differences are common, the reasons are not what you think. The difference in cores causes a very large difference in the inductance value. A blocking oscillator frequently is used in a audio or other low frequency applications that do not require a sine wave output, or actually need the pulse-like nature such as an old television vertical sweep circuit. A Hartley oscillator usually is used in high frequency and RF applications that need a sinewave output, like a wireless microphone. On paper, either oscillator circuit can use either inductor type, but in practice the natural characteristic differences between the two types of inductors make them preferable in two different kinds of applications.

    ak
     
  9. Mark Hughes

    Thread Starter Member

    Jun 14, 2016
    97
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    @AnalogKid It's been a good 15-20 years since I've studied these circuits and an equal number of years since I remembered which circuit was named what or for who. Do you have a favorite source (book, website, etc...) that you could recommend as a reference? I was half-tempted to describe the movement of charges (or energy) around and through the circuit but quickly decided that would lead to death by pitchfork in an online forum. (Don't get me wrong, I'd figure out how to make a tidy sum selling online pitchforks).

    And am I correct in calling this a "Single-swing blocking oscillator circuit" or should it be something else?
    http://www.allaboutcircuits.com/uploads/articles/AudibleCircuitProbeSchematic.jpg
    [​IMG]
    Thanks,
    Mark
     
  10. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Yes....though it somewhat resembles a coal pit oscillator, it is actually a classic blocking oscillator.....often used for code practice osculators.
     
  11. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    That's a new on on me. What is it?

    ak
     
  12. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Colpitts....just me being silly. Which I hardly ever am. :)
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You're just a 'mine' of information!:)
    Max.
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    1981, and happens to originate from my old home town in the UK.:cool:
    Max.
     
  15. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Yep, I'm a regular suppository of knowledge. :)
     
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