Increasing the power of the single transistor Pleiades BD139 amplifier at 12V only

At your risk. Please take all safety precautions. A multy turn ratio output transformer (it must be air gaped but so far tests have been donbe without introducinbg air gap) was created with secondary 9speaker side) inductance of about 40mH. Various collector volatges were tried including 12v, 24V, 36V, 48V. 24V sounded very nice, see also the Pleiades 2N3053 amplifier. The BD139 due to higher hFE is more sensitive needing less bias current and less music input voltage. Using the 5:1 ratio at Vb=12V requires about 27mA collector current for great class A operation (electrons flowing all time) sound. Rb=71Kohms. It sounds loud and clear. The schematic is just a single transistor with air gaped output transformer in the collector circuit, and just a bias resistor from collector to Base. The 2N3055 (not to be confused with 2N3053) sounded briliant as all the other mentioned transistors but it seems even more sensistive than 2N3053 and even BD139. But it blocked at Vb=48V for no reason known to me. It sung at Vb=24V. Higher Vb was tried with higher transformer ratios eg 7:1, 10:1, 13:1, 17:1. The laminations used were EI grand orient by Tranceria Ligure bought from Stefos in Athens.