It really is a two-stage tube amplifier that can give you and true tube amplifier feel to your transistor nicely. The profit booster does NOT hold any semiconductors. It is based entirely on the tube 12AU7 Beckmann Gainbooster is a pedal that was intended to work for musical instruments mainly in the blues context. The unit is based on the tube 12AU7 which has a very nice character. The sound picture can be adjusted with the "GAIN" knob, you can then reach a fairly strong output level that causes the amplifier to cut. To adjust the tone, there is a steering wheel "VOLUME" that allows you to drive distantly but without cutting the input of the amplifier again. To get a little softer "jazz" sound there is no "TONE" it is just a fine touch of the sound..