I've seen several schematics but never an actual device.
National has a couple of schematics in the LM317 data sheet where the 317 is a current source and a LM195 or LM395 for an output transistor.
I like the idea. The resulting amp is bullet proof. LM395T is $3.95. LP395 is the same thing in a to92 case and costs about $1.50
Using the to92 case parts we could have a tiny amp. Edit -- This is a class A amplifier. Device is good for 100mA / or 1Amp in the larger package. Amp output power would be less.
It is also possible to put an audio signal into the adjust pin and use the 317 as an audio amplifier.
Brooksie has another idea here:
All this got me to thinking. The 317 can be had in a variety of small packages. One 317 costs about 80 cents. It is also rugged. Output shorts and overloads won't kill it.
It should be possible to build a small easy to build head amp with these parts.
But how will it sound?