The quintessential triode amplifier. It is not necessary to use Western Electric 300B vacuum tubes. Current (new) production 300B tubes like the Electro-Harmonix 300B and the JJ 300B sound wonderful at a fraction of the Western Electric 300B price. A direct coupled driver stage and a low mu triode array are the specific reasons why this design works so well. Good output transformers are the key to good performance. Magnequest FS-030 or Tango XE-60S are good choices.
The schematic for the 300B Single-Ended Vacuum Tube Amplifier is shown below. Using audio output transformers with a primary impedance of about 3000 to 3500 ohms you can expect about 8W of output with at about 2.5% THD.
The power supply use a 5U4-GB tube rectifier and a C-L-C filter. There is more information about power supply design with tube rectifiers in the Power Supply Design for Vacuum Tube Amplifiers article.
Stephen (sampleaccurate on the forum) put together a 300B SET amplifier following the above direct-coupled 6SN7 driver / 300B SE amplifier schematic. Photos of his build are shown below and additional information is available on the forum in the First DIY amp FINISHED - 300B SET - works! thread.
6SN7 / 300B Single-Ended Triode (SET) Tube Amplifier
6SN7 / 300B Single-Ended Triode (SET) Tube Amplifier - Rear View
6SN7 / 300B Single-Ended Triode (SET) Tube Amplifier - Underside View
Additional photos and information is available on the forum in the First DIY amp FINISHED - 300B SET - works! thread.
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