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

 

It is a blocking oscillator

 

@DickCappels Mystery solved. Thank you so much!

 

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?

 

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.

 

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.

 

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.

Thank you sir. I too am waiting for it to download.

 

The blocking oscillator has a metal-core inductor, whereas the Hartleys seem to have air-core inductors,

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

 

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

@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

Thanks,
Mark

 

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

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

 

a coal pit oscillator

That's a new on on me. What is it?

ak

 

That's a new on on me. What is it?

ak

Colpitts....just me being silly. Which I hardly ever am.

 

Colpitts....just me being silly. Which I hardly ever am.

You're just a 'mine' of information!
Max.

 

Tandy have put the manual online. That's cool, since this kit predated the internet by a decade, at least.
.

1981, and happens to originate from my old home town in the UK.
Max.

 

You're just a 'mine' of information!
Max.

Yep, I'm a regular suppository of knowledge.