Small but nice !
With the solgan "Wolf in sheep's clothing" Mr. Nixie presents a very tiny tube headphone amp but it's really a deep me, even if it's small outline footprint of only 85 x 85 mm.
2 pcs. 6N28B-V miniature dual triodes from Russian military surplus operate as preamplifier stages to a stereo Class A MosFet impedance transformer stage with 300 mA idle current each. These triodes are specially designed to operate on low anode voltages, have an ultra long life, less microphonic noise and are shock proof. BTW, Pete Millet's "Starving Student" amplifier was the template for this improved circuity.
Compared with many similar amplifiers from Chinese production, which operates the 6922 triodes with only 1/10 of the suggested anode voltage, the tubes in this tiny amplifier operates with 45 V and therefore exact within their specifications; and this you'll just hear.
The measuring datas approve the listening testings: light, soft and with a warm sound. And this tiny amplifier can provide real power if needed without sounding annoying or nasty.
Der Frequenzgang ist faktisch linear, egal ob an 150 oder 32 Ohm, der Innenwiderstand ist unter 1 Ohm, die Klirrkomponenten - Röhrentypisch mit viel K2 - steigen erst zur Aussteuerungsgrenze auf über 5 % an, und sinken linear bei geringerer Aussteuerung bis auf weit unter 0,1 %.