One pair of 300B Single-Ended Triode (SET) mono amplifiers, DIY-built in a home laboratory/kitchen here in Menlo Park. Nice curly-maple frames with an aluminum chassis plates. Output: ~8 watts.The 300B tubes are Sophia Electric Princess Meshplates run at 390vdc B+ @ 66ma; the driver tubes are the 5842 / WE417 run at 150vdc B+ @ 10ma. Safe, conventional 300B SET design, running at recommended tube operating points. Chassis has a bottom cover, not shown. This is an easy-running, low-maintenance build: in future, a skilled DIYer or regular hifi technician can easily decipher my circuit schematic for any repairs/improvements down the road. Output transformers are 3.5K-impedance James Audio 6123HS with 8-ohm and 16-ohm taps. Power supplies are solid-state CLC-designs on vintage JAN (Joint Army-Navy) transformers, with ElectraPrint chokes on the 300B's filament and B+ supplies. Low ripple and low noise. Power-on procedure is first warmup by 5v tube filament circuit with neon indicator, followed by hi-volt B+ plates circuit, both by individual switches. Other elements: Selected use of pure silver and copper wire in point-to-point wiring. Resonance damping of chokes and capacitor damping of diodes. Metal backplate to secure the power and speaker taps. Buffer handles were placed on the backplate and above the filament/B+ switches that protect the connections from bumps and accidents. Rubycon Blackgate cathode capacitors. Dale/Vishay wirewound resistors. One amp has two sockets at the driver tube position, but only one is active. Both amps have former PIO cap mounts now covered by matching plates. All parts are high quality from selected makers known in DIY hi-fidelity for good-sounding components.
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