Pocket Rocket bass preamp, 9v headphone amp
 
Cool rare unit, lets you play bass with a set of headphones and hear yourself anywhere. Runs off 9 volt battery, has normal, bright, and distorted settings, plus tone and volume controls. Also has an aux jack which functions as an aux input and a low level output for recording, etc (or so the manual tells me). so you can use it as a preamp into another amp.
 
http://www.pocketrockit.com/pdf/former/ownersManualBASS.pdf
 
Three inches long, weighs almost nothing, the input jack rotates so it can sit flush for storage and stick out to plug the unit into your bass. Headphones not included, has standard small stereo headphone jack.
 
$25 plus shipping

I had one of these,great practice tool.

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