Hello,
I've been building the 50W amplifier design from the book Understanding Electricity and Electronics by G. Randy Slone. I expect this design is far less complicated than the norm for this forum and I hope somebody will be able to help me understand why this doesn't seem to work. I am a beginner in amplifier construction and trying to learn as I go, perhaps a fool's errand - that's the reason why I'm using this book which attempts to teach amplifier concepts from scratch.
I have had to make several component substitutions due to the lack of availability of some of the components listed in the BOM:
NTE287/NTE288 --> MPSA42/MPSA92
MPF102 --> J111
2SC3280/2SA1301 --> 2SC5242/2SC1962
I have found and fixed errors in both the schematic and in the PCB artwork supplied in the book, and it wouldn't surprise me if there are still error(s) that I'm not knowledgeable enough to understand.
This is the schematic:
According to the design notes, the voltage on the output terminals should be adjustable using P2 down to around 0v to balance the amplifier. However, it stays around 20v to 30v no matter what. The power transistors Q16 and Q17 get hot, but nothing else does. I have not connected anything to the output.
The voltage between TP1 and TP2 is around 0v after adjustment with P1 (although it is all the way to one end of its range), which is what the notes expect.
The behaviour is similar when simulating the circuit under ltspice, although the exact voltages are different. In simulation, I see the output rise to 29v with all potentiometers at the centre, and the voltages on either side of C5 are 27v and 32v, which seems wrong to me. The voltages at the test points TP1 and TP2 are both about 32v.
Any help at all would be appreciated very much!
I've been building the 50W amplifier design from the book Understanding Electricity and Electronics by G. Randy Slone. I expect this design is far less complicated than the norm for this forum and I hope somebody will be able to help me understand why this doesn't seem to work. I am a beginner in amplifier construction and trying to learn as I go, perhaps a fool's errand - that's the reason why I'm using this book which attempts to teach amplifier concepts from scratch.
I have had to make several component substitutions due to the lack of availability of some of the components listed in the BOM:
NTE287/NTE288 --> MPSA42/MPSA92
MPF102 --> J111
2SC3280/2SA1301 --> 2SC5242/2SC1962
I have found and fixed errors in both the schematic and in the PCB artwork supplied in the book, and it wouldn't surprise me if there are still error(s) that I'm not knowledgeable enough to understand.
This is the schematic:
An externally hosted image should be here but it was not working when we last tested it.
According to the design notes, the voltage on the output terminals should be adjustable using P2 down to around 0v to balance the amplifier. However, it stays around 20v to 30v no matter what. The power transistors Q16 and Q17 get hot, but nothing else does. I have not connected anything to the output.
The voltage between TP1 and TP2 is around 0v after adjustment with P1 (although it is all the way to one end of its range), which is what the notes expect.
The behaviour is similar when simulating the circuit under ltspice, although the exact voltages are different. In simulation, I see the output rise to 29v with all potentiometers at the centre, and the voltages on either side of C5 are 27v and 32v, which seems wrong to me. The voltages at the test points TP1 and TP2 are both about 32v.
Any help at all would be appreciated very much!