At your risk. All safety precautions should be followed for any voltage or current.
Operating point used is 70V, 12mA.
Output transformer is a Sowter SK05s.
Amazing smooth sound. Big bass. Amazing mid and treble. Very smooth sound on very low noise ambience.
A schematic similar to Pleiades V6 is used but pull up grid bias is with a 10MΩ resistor from filament centre tap to grid. A 1:7 turn ratio input transformer is used. Electron tube is triode connected ie grid 2 connected to anode.
For some strange reason the one transistor Pleiades BD139 at operating point 10V 50mA sounds about 3 times louder. Not as smooth but could the grainess be from the CD player?
Perhaps electron tube bias should be changed to cathode resistor bias. Grid leak must be preventing overload created harmonics due to the change in bias ie amplification by the grid rectification effect affecting DC grid bias. Progressive overload can be part of the loudness of sound, see Russel O. Hamm.
Would the best comparison for an electron tube vs transistor be one active device amps with no feedback fed with the best live signal? For example musicians playing in another room and sound picked up be a world class mic? A Pleiades filter added in the signal path if needed for flat frequency response from producer's brain to listers brain. [Lowe, Morgan]
References:
Tubes vs Transistors (vs op amps), Is there an audible difference? - Russel O. Hamm - JAES
Sound Picture Recording and Reproducing Characteristcs - D. P. Lowe, K. F. Morgan - Journal of the society of Motion Picture Engineers
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