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Different with 12ax7, subminiature is safe in vibration. At same time, it's volume is smaller ,we use 42v power supply. in order to play without power, we use 12 volt Lithium battey and Charger . please hear sound ,play by Bob http://www.kldguitar.com/sound/effec...t-bob-play.mp3. http://www.kldguitar.com/sound/effec...ooster-BOB.mp3Thanks Bob