Headphones

We are used to seeing the latest generation of pentodes gracing the royalty of high-end audio's tube amps, even if popular bulbs like the KT120 and KT150 are more properly described as Kinkless (beam) Tetrodes. But there are also subsets of pentodes specifically designed for low power applications, and the PL95, with its low 300mA heater consumption, is one such example [seen flanking the ECC81 triode, inset picture]. Auris Audio can supply the Euterpe with an alternate EL95 tube but its heater filament has different requirements and so you must select between them via a toggle switch on the top of the black chassis.

The tube is configured in single-ended mode here, so power output is restricted further. Moreover, while the Euterpe's source impedance may be switched, the 'Low' setting is still rather high at 68ohm, resulting in a 7dB loss in output driving the likes of the HiFiMan Aryas [HFN Aug '19] or, creating greater subjective uncertainty, producing equivalent swings in response if the headphone has a low and variable impedance trend. For predictable results, stick to high impedance 'phones. PM