Srajan Ebaen
Financial interests: click here
Sources: 27" iMac with 5K Retina display, 4GHz quad-core engine with 4.4GHz turbo boost, 3TB Fusion Drive, 16GB SDRAM, OSX Yosemite, PureMusic 3.01, Tidal & Qobuz lossless streaming, COS Engineering D1 & H1, AURALiC Vega, Aqua Hifi Formula, Fore Audio DAISy 1, Apple iPod Classic 160GB (AIFF), Astell& Kern AK100 modified by Red Wine Audio, Cambridge Audio iD100, Pro-Ject Dock Box S Digital, Pure i20, Questyle QP1R]
Preamplifier: Nagra Jazz, Vinnie Rossi LIO (AVC module), COS Engineering D1, Wyred4Sound STP-SE Stage II, Trafomatic Audio Lara [on review]
Power & integrated amplifiers: Pass Labs XA30.8; FirstWatt SIT1, F5, F6, F7; Crayon Audio CFA-1.2; Goldmund Job 225; Aura Note Premier; Wyred4Sound mINT; Nord Acoustics One SE Up NC500MB monos; Linnenberg Allego monos
Loudspeakers: Audio Physic Codex; Albedo Audio Aptica; EnigmAcoustics Mythology 1; Boenicke Audio W5se; Zu Audio Druid V & Submission; German Physiks HRS-120; Eversound Essence
Cables: Complete loom of Zu Event; Ocellia OCC loom: KingRex uArt, Zu and LightHarmonic LightSpeed double-header USB cables; Tombo Trøn S/PDIF; van den Hul AES/EBU; AudioQuest Diamond glass-fibre Toslink; Black Cat Cable redlevel Lupo
Power delivery: Vibex Granada/Alhambra and Three 11R
Equipment rack: Artesania Audio Exoteryc double-wide 3-tier with optional glass shelves, Exoteryc Krion and glass amp stands [on loan]
Sundry accessories: Acoustic System resonators
Room: Rectangular 5.5 x 15m open floor plan with two-storey gabled ceiling, wood-sleeved steel trusses and stone-over-concrete flooring
Review component retail: €9'000

The beating pulse of the +.
Querying Trafomatic boss Sasa Cokic on the key difference—between 100wpc Eos and 150wpc Eos+—"mostly the more open and transparent sound with stronger firmer bass due to my new ultralinear output transformer technique. Eos+ also runs Tungsol KT150 with higher plate dissipation than the standard KT120 Eos. That means a larger window of class A bias." To keep their chassis to attractive dimensions, the Eos models move their DC trap and 800VA power transformer for the output tube anode voltage into a separate 11kg box connected by 4-pole umbilical. A side benefit is reduced stray radiation from a beefy power trafo, on critical signal-path circuitry and the double C-core output transformers. Flanked by the latter, the centre canister on deck houses the CLC filters with 10H chokes and a smaller toroid for the bias and heater circuits. The four small valves are paired ECC99 and 5687. A rundown of the usual specs hits 1.2Vrms input sensitivity, 82dB S/NR, 100kΩ input impedance, 0.03% THD at 1W and 3% at full power and -1dB bandwidth of 10Hz-100kHz. The main enclosure weighs 27kg and measures 45x35x23cm WxDxH whilst the power supply takes up 15x30x20cm. A vertical plexi shield first seen in the Kaivalya monos acts as transparent tube protector if inserted.

From ARC to Octave, from Lab12 to Trafomatic, today most makers of valve amps have a high-power KT150 representative. Ten years ago, perhaps 6550 might have done that job. With KT shorthand for kinkless tetrode, this newer elongated egg of a power bottle belongs to the same family as the KT88. In his Brazilian Audiopax amps, Eduardo de Lima famously cloned those to measure and sound like a triode. Given the 150's quick ascendant to widespread popularity, I asked Sasa—he uses them also for his 200-watt Noa monos—on just what makes this Röhre so attractive. Does it roar like the German word might suggest? Surely raw power alone wasn't the only allure. Or was it? Somewhat.

The down-facing grids are simple vents, not fan openings. On the review loaners, the spiked footers were flat aluminium cylinders finished with felt pads.

"Compared to KT88, 6550 or similar pentodes, at 70 watts the KT150 has much higher anode dissipation. Also, that specially designed glass envelope improves thermal dissipation and eliminates all microphonics because the bulb has no flat surfaces. Higher dissipation gives more power in pure class A (~20 watts) where a 6550 would just make 7-8W. Sonically I didn't notice a big difference but of course then I use 6550 in different designs so couldn't tell you exactly. What I can say is that with Eos+, the bass is much stronger and better defined than in 6550 applications. In that sense it gives you a different tonality. The overall circuit concept was the minimum number of active and passive components with minimum negative feedback. The ECC99 drivers work as anode followers while the cathodyne 5687 inputs handle voltage gain and phase splitting. Those tubes have low output impedance to work well in that application. The KT150 connect to the output transformers in ultralinear mode with just 20% separate windings for G2 which usually would be 43%. Also, I use cathode feedback directly from the output transformers. This combination of NFB and low-value UL mode with my new winding scheme extracts the best triode and pentode attributes, namely low distortion with high power. The 'secret' is actually the precise ratio of these two aspects."