The Wien bridge oscillator is usually denoted with a bulb to balance the gain of the system and produce stable oscillations.

Unfortunately, I don't have any bulbs, so I'm curious what a good modern replacement is, and how one would design such a replacement.

wein bridge oscillator for wikipedia

  • \$\begingroup\$ Read Andy's comment about JFETs here: electronics.stackexchange.com/questions/78388/… -- which is also a link to the right of your question. \$\endgroup\$ – jonk Sep 9 '16 at 20:19
  • \$\begingroup\$ Also, some discussion about using a JFET part way down this page: learnabout-electronics.org/Oscillators/osc34.php -- just from a quick google search for you. \$\endgroup\$ – jonk Sep 9 '16 at 20:21
  • \$\begingroup\$ I was kind of hoping for an expansion of that idea. \$\endgroup\$ – Andrew Spott Sep 9 '16 at 20:21
  • \$\begingroup\$ Can you expand your question to include the jfet topology and by then talking about the aspects of the jfet circuit where you need more thought added? Or are you fishing for a still different answer? \$\endgroup\$ – jonk Sep 9 '16 at 20:24
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    \$\begingroup\$ Jfets aren't the only option for agc, so I would rather not limit answers to just jfet agc circuits. I'm going to let this question fester for a bit (I don't have time to rewrite it right now), but maybe I'll refocus it later. \$\endgroup\$ – Andrew Spott Sep 9 '16 at 20:27

I believe you might benefit from Linear's Application Note 43f. Look for the section on Wien bridge oscillators. Jim Williams tried replacing the bulb with JFETs as well as a photocell "vactrol". Essentially, anything that has a nice linear transconductance would be a good candidate.

If anything, the app note is an excellent read and Jim Williams was a rock star :-)

  • \$\begingroup\$ The same techniques are explained in the 3rd edition of Art of Electronics. \$\endgroup\$ – Mike Spivey Sep 10 '16 at 7:06

A PTC thermistor is the other replacement option if you want to keep the simplicity of a two terminal passive.

Active level stabilisation is a good and useful thing, but there is sometimes much to be said for simple and crude, and often good enough is all that is needed.

Regards, Dan.

  • \$\begingroup\$ How do I choose said thermistor? \$\endgroup\$ – Andrew Spott Sep 10 '16 at 19:54

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