There's two ways to use this. One: run it into the FX loop of your amp, so you've got a master volume control over your power amp. That's super handy if you've got a loud amp with no master, like a JTM45 etc. Or, run it on the front end as a simple passive volume control. 

Model: Glow Baby Tube Amp Master Volume
Made: Australia, recent model
Serial: N/A
Type: volume/expression
Power Input: standard 9v DC centre-negative (supply not included)
Accessories: none

Condition notes: used, no major marks. Tested and fully functional.
Overall: very good condition (8/10)