Mike KC7IT pointed out that the AF amplifier chip in my Sawdust regen receiver is actually a TL431 voltage regulator. Mike writes: “It’s using the voltage reference input as audio in, and the voltage being regulated as the audio out.” It works great as an audio amplifier, and with just three terminals it is a lot easier to use than our normal LM386 or 741 chips. I’d never seen a regulator used this way.
Here’s the data sheet: http://www.ti.com/lit/gpn/tl431
And here are a couple of sites that discuss this very interesting repurposing:
http://theradioboard.com/rb/viewtopic.php?t=6733
http://techlib.com/electronics/audioamps.html#TL431
Bill its not only the TL431 that can be used this way. The 78L05 can also be used at RF and AF see http://www.sm0vpo.com/ 73
Interesting. with the sot-23 version one can stuff 55dB of AF gain in a square centimeter. Naturally I now have 50pcs to-92 version and 50pcs of the sot-23 version on a slow boat from china.