Limit to how powerful a single transistor power amplifier can be?

 At your risk.

Signal path:

Constant craving - K. D. Lang on CD - Sony CD Walkman line out or Philips CDR 870 line out - Pleiades 2N3055 power amplifier  with various output transformer ratios, Vb= 9V or 12V or 24V - Marantz Imperial 5C

Trying to increase power output by increasing Collector power dissipation (by changing Vb or base bias current), increased loudness but not as much as expected while transistor with a heatsink was getting warm.

It seems there is a limit as transistor amplifiers need signal power input due to their low input impedance which depend on how much the collector circuit is loaded. There is hfe (ratio of collector current to base current), and if the collector current is increased the base current must be increased to and the same applies to a changing base collector or base current i.e. a signal current. 

A CD player at line out for example can give a certain amount of small power output.

Connecting the sigle electron tube Pleiades EF183 power amplifier at 2.4W plate dissipation to the CD Walkman line out gave by comparison a huge sound, surprisingly loud and big. The reason seems to be that an electron tube does not take power from the signal source as it has a very high input impedance.

So it seems the winner will be the electron tube.

A Darlington can be tried. But it is 2 transistors although the configuration or connection between them is a simple as possible.

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