It shows typical (not worst case) saturation voltage below 0.8V with Ic=10A and Ib=1A, which isn't that bad, I think. I don't have the original RCA data book at hand now, but I think the actual Onsemi datasheet is almost identical. They once have been called work horse of electronics. However, I've used these transistors at times, when few better devices have been available and of course, you can make profound designs with them. Regardig 2N3055 data, I already mentioned previously, that the minimum specified current gain results in a very poor circuit behaviour. Personally, I also don't use inverters normally, except for some outdoor industrial projects.

I don't want to doubt anything you said about advantages of modern inverters. I have never used an inverter because my electricity is very reliable. Many inexpensive Chinese inverters use a pure-sine-wave circuit and they have voltage regulation so the output voltage does not change when the load changes or when the battery voltage runs down. Special small ferrite high frequency transformers are used. Its circuit is a little more complicated than a square-wave inverter.ДЄ pure-sine-wave inverter operates without making much heat and has a very complicated circuit. You cannot simply increase the voltage of a square-wave inverter because then incandescent lights and heaters will draw too much current.ДЄ 'modified-sine-wave' inverter has a rectangular waveform which has the average and peak voltages the same as a sine-wave and most products work fine from it. Many electronic products incuding power tools don't work properly on the square-wave output of a simple inverter because they rely on the much higher peak voltage of a sine-wave from the mains. The Mosfet doesn't need any base current.

The power output of the inverter will be very low.ДЄ modern Mosfet like an IRFZ44 (there are better ones) has a max saturation voltage loss of only 0.28V at 10A and heats with only 2.8W. The voltage loss times the current equals heating of up to 30W. That is a lot of loss so the design must account for it so the output voltage will not be too low. You should try, if 50 or 100 ohm in place of the 1N5402 reduces the idle current.ДЄn old 2N3055 transistor has a max saturation voltage loss of 3.0V when its collector current is 10A and its base current is 3.3A. This may be tolerable for a low frequency inverter, but also the output transistor have no parallel base resistors, thus switch-off is rather slow. One drawback of the circuit is it's 50% duty cycle without any means to prevent simultaneous current flow in both output branches, e. You need more paralleled or stronger (e.g. Cause 2N3055 current gain is unspecifed above 10 A, a profound design would never calculate more than 10 A per output transistor, resulting in about 30A * 10 V = 300 W maximum output power. 470 ohm.Д«ut please notice, that with 2N3055 absolute maximum current of 16 A, you still won't achieve the intended 600 W. The SK100 3.3k base resistor should be also reduced to e. I see, that SK100 has a 500 mA IC rating, cause it's operated as a switch, reducing the 150 ohm resistor to 33 ohm or even less should be possible without changing the driver. Increasing the drive current is a way to get more output power from the circuit. To be operational by design, a circuit must consider specified minimal current gain. A bit more, than the reported 160 W, but actually, there are switching and transformer losses and a magnetizing current, too.ДЇurthermore, the 2N3055 may have a much lower current gain without being a fake product, completely within manufacturer specification. Neglecting transformer magnetizing current and any switching losses, and assuming only 2 V voltage drop for the darlington, you get 10V * 22.5 A = 225 W total output power. current gain of 15 and 7.5 A output current.

a current gain of 75 and sources 1.5 A, 0.5 A to each output 2N3055. The pre-driver is supplied by 5 V and may source around 20 mA (3V/150 ohm) to 2N3055 driver. Calculating with typical 2N3055 current gains, you can easily see, why.

I don't see any power or current notice in the schematic, and I basically doubt that it's capable to deliver 500 W in the present dimensioning. Paralleling of BJT without emitter resistances isn't guaranteed to give balanced current distribution normally.However, in this case, I think it's O.K., cause the CE saturation resistance achieves a balance. I understand, that you connected three 2N3055 in parallel as mentioned in the text.

2n3055 transistor specifications