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Against this backdrop, Auris Audio's ambition seems to be carving out a parallel niche to Trafomatic Audio's precedent of well-liked valve gear from Serbia. In fact Trosic and Cokic are friends. Sasa provides most the output and power transformers to his domestic colleague though Auris Audio also wind their own depending on model.
As their current top amplifier, the Forte monos list parts like Mundorf silver/gold oil-filled caps and silver WBT terminals. Upon request they can be fitted with Lundahl-coupled XLR inputs.
Related and often hot-swappable with a 5881 and 6L6, the 6550A is a powerful and rugged octal pentode popular with guitar slingers. The bottle dates back to General Electric whose data sheet specifies 42 watts of plate dissipation and 500/660V of DC plate voltage in triode/pentode connection. There's 6 watts of average screen dissipation, 190mA of DC cathode current and 0.05MΩ grid resistance in fixed bias and 0.25MΩ in cathode bias. The glass envelope can reach up to 250°C at its hottest point.
One 6550A is capable of 12.5 and 20 watts in single-ended triode or pentode mode. A pair of 6550 in class AB1 push/pull can achieve 40/60 watts with cathode bias and 77/100 watts in fixed bias. In ultra-linear mode those figures reduce to 34 and 70 watts respectively. This tallies perfectly with the Forte monos' class A power rating.
To retain their design's clean lines without parking the mains switch where rack users often can't get to it, Auris mount theirs on the belly beneath the recessed logo window. This visually confirms during the day with a downfiring pair of blue LEDs whilst at nights the tubes themselves should be sufficient evidence on whether the amps are live or not.
Inside the leather-wrapped casing there is a red mother board whilst a sealed case with presumably two large chokes is mounted directly to the bottom plate.
Here one also finds additional fuses aside from the mains fuse integrated with the power IEC.
Along its inside walls, the wooden frame is properly lined with metal.
The area directly behind the terminal plate is occupied by the sealed box mounted to the bottom plate. The 5 probe points for tube bias connect to four blue trim pots situated adjacent to each 6550 on the top panel.
