• Mike Morrow's Morrow Audio 300B1S monos - $6,500/pr;
• Hans-Jürg Dorn's Althea Musica Royale 300B Concept Mono;
• Sun Audio's SV-300BSM - ¥810,000;
• SAC Thailand's custom-order WE 300B monos;
• WAVAC's EC-300B, MD-300B and MD-300Bm - from $8,500 to £16,500;
• Promitheus Audio 300B monos - $1,500;
• Audio Note UK Kegon - $49,000;
• and the Border Patrols with outboard power supplies - €10,600 for the paralleled Model S20.
• Allnic from South Korea
• TruLife Audio from Greece, €1000 per watt, interstage transformer bandwidth beyond 2MHz

For kits or published DIY circuits with interstage transformers, reference AudioNote UK kits and Lynn Olson's Nutshell HiFi Karna (6H30 or 5687/7044/7119 input, 45 driver). For further 'open' circuits, Nobu Shishido's IT-coupled 300 SE Topology was published in Glass Audio in 1994. For perhaps the most generic non-IT 300B SET circuit, think 3-stage affair running 6SN7 dual-triode input/drivers. Much present Chinese offerings seem to fall into that category. Other designers don't see the need for two voltage amplification stages with their higher complexity and cancellation of harmonics. They favor less stages. The earliest 2-stage circuits used pentode drivers like Western Electric's legendary movie house amps. Shishido used 6L6s. Gordon Rankin's 2-stage Wavelength Cardinal sports a shunt-regulated push-pull stage (SRPP) to drive its power triode. Other 2-stage topologies use single rather than dual triode drivers. Japanese audiomaniacs seem fond of the classic Western Electric 417A/437A drivers when transformer-coupled to the power triode, championed particularly by Shishido and Sakuma. SAC too adopted this recipe for its current flagship monos. Then there's direct-coupling and the Loftin-White approach.


To avoid urban myths on whether capacitor or transformer coupling is ultimately superior, I asked Sasa Cokic why they went IT for their statement efforts. The part's formulation had delayed the amps' launch more than once, with an earlier Cokic e-mail mentioning an eighth iteration of the transformer. This mirrored what the Japanese whispered all along. Only the very finest iron (they favor Tango and Tamura) does this circuit juncture justice. Hence the expense and relative rarity. To get it right is mission critical and more challenging than simply wishing away those coupling caps. Considering how few amplifier designers double as magnetics designers further explains why this subject remains less visited. And why Trafomatic Audio is wonderfully positioned, specializing in transformer manufacture first but now designing electronics to showcase some of those transformers. (The operative term is some. Trafomatic also makes "10KVA monophase transformers for primary and secondary voltages up to 1000V, three-phase transformers from 5KVA to 50KVA and electro-resistance welding transformers from 18KVA to 75KVA".)