Overdrive Pressure Control Valve (size+0.015 mm) A6GF1 A6LF1/2/3 A6MF1/2
The Hagerman Tube Overdrive Pedal - Loaded with a Mullard 12AX7! - YouTube
ValveDrive - EBS ValveDrive - Audiofanzine
Amazon.com: Sondery Overdrive Guitar Effect Pedal, Tube Overdrive of A Valve Combo Amplifier Sound - True Bypass, 2 Modes of Boost and Normal - Mini Size, Art Design Series : Musical Instruments