This is a power amplifier for driving low impedance headphones. The schematic design I arrived at was one that has the least amount of components in the signal path to best preserve the source signal through the amplifier.
This design involves only 5 components per channel within the signal path. 1 vacuum tube, 1 resistor, 1 cathode bypass capacitor, 1 volume attenuator, and 1 output transformer. With only one stage for amplification, great attention must be paid to assure that these few components contribute appropriately without introducing unwanted distortion.
Since the majority of the task of amplification relies on the singular vacuum tube stage, a special valve must be selected to operate within the necessary range without saturating. The recommended D3A Pentode vacuum tube is known for wide band telecommunication instruments for the German Post Office in the 1950s.
When the D3A is treated like a triode and stepped down by a nice quality output transformer, it provides excellent performance for the task of driving low impedance headphones.
The minimal number of components are arranged relative to each other in a way that their emitting magnetic fields do not interrupt one another. Each channel is symmetrically separated so that each transformer is given as much distance as possible from one another to avoid unwanted crosstalk.
The finned enclosure allow plenty of air circulation while acting as a light RF shield to protect the signal as well as protecting the user upon accidental interactions.
The amplifier works accordingly. The cable is handmade.