Boxboro, MA USA
Ampeg B-15N amplifier is equipped with Thiele tuned-port cabinet, from 1972.
6L6GC tube bias
How-to here: Re-bias your amp - it's not hard, you just need a soldering iron and a new resistor. Also, info about the bias supply filter capacitor and how to replace it.
Jason Buchanan - firstname.lastname@example.org