FI 300B Amplifier. The fi 300B amplifier is a high current three stage design built on an open frame chassis which completely seperates amplifier and power supply functions. The 6SN7 dual triode contains a voltage amplifier direct coupled to the driver stage. This is coupled to the 300B output stage with a Hovland film and foil capacitor. The chassis construction makes possible an extremely short signal path which is hand wired point-to-point with 99.99% pure silver. Output transformers are MagneQuest FS030. As in all fi amplifiers, no negative feedback is used. Output power is 9.5 Watts.