So, I am trying to breadboard this amp

[Hextejas]

And other than a bit of heat, thatscall the output. I don't know how to debug it. Plus I have a question.
I have a small scope and I can see the 1k Hz test wave until it hits the BC550C. Where else should I look and for what ?
I did not design this but others have built it successfully and liked it so I thought that I would give it a try.
What is the reason to put the sine wave onto the gate of the BC550C ?

[LeoTech]

Well, are you sure this schematic is correct?

Because for this to be an amplifier it needs an input, output and a power supply, and as far as this particular schematic goes, there is no output.

Although I would presume that the output is the 8 ohm resistor (R11), pretending to be something like a speaker or so? Please clarify this and I(we) will be able to assist you further.

Leo

[Audioguru]

What is the reason to put the sine wave onto the gate of the BC550C ?

You need to learn about transistors to understand how the circuit works.
The BC550 has a base for its input, not a gate. A BC550 is a bipolar transistor, but a Mosfet has a gate for its input. This circuit does not have a Mosfet.
The output power of this amplifier is very low but it produces a lot of heat because it operates in class-A. Its current is probably too high for the contacts on a solderless breadboard, solder the connections together on a pcb instead.

[Hextejas]

Well, are you sure this schematic is correct?

Because for this to be an amplifier it needs an input, output and a power supply, and as far as this particular schematic goes, there is no output.

Although I would presume that the output is the 8 ohm resistor (R11), pretending to be something like a speaker or so? Please clarify this and I(we) will be able to assist you further.

Leo

Thank you Leo, and that 8 ohm resistor is supposed to represent the speaker. That was my reading. I tried asking the author but got no response

[Zero999]

The trouble is with the way it's biased, the collector voltage will be heavily dependant on the Hfe. My guess is a couple of volts, at most, so far too low.

Reduce the resistor values and add a capacitor to keep the base bias constant, irrespective of the signal. See attached. For convenience, I just used a constant current source, rather than the LM350 circuit.

The circuit is fine for very low output levels, but will distort horribly, at higher amplitudes. Being class A it's also very inefficient and is a poor choice for driving a speaker. I've used a similar design, in a mic. pre-amp and it was fine, but wouldn't consider using it as a power amplifier!

Removing C2 will make it more linear, at the expense of gain. Another option is to AC couple a resistor from Q2's collector, to Q1's base, which will reduce the gain and the distortion, but not as much as removing C2.