Limited Budget

[TeacherTom]

Hi All
I am a teacher at a Tech Center for junior and senior high students and have a limited budget. I have several 2n3055 and other pnp & npn transistors. I need audio amplifier schematics for teaching using the transistors I have. There are several 100W and over schematics but they use a 2sk134 mosfet and I can't find those in my area of the US. Does anyone out there have any schematics for an audio amp using generic type of transistors.

 

[Mikebits]

No textbooks? That is low budget. Google is free though...

 

[kchriste]

If you have a limited budget, then the cost of the transformer is going to be what kills you, not the transistors. Besides, the 2N3055 is not very well suited for the application but it will teach your students about distortion.

 

[Leftyretro]

Hi All
I am a teacher at a Tech Center for junior and senior high students and have a limited budget. I have several 2n3055 and other pnp & npn transistors. I need audio amplifier schematics for teaching using the transistors I have. There are several 100W and over schematics but they use a 2sk134 mosfet and I can't find those in my area of the US. Does anyone out there have any schematics for an audio amp using generic type of transistors.

Hi Tom;

While maybe not a current popular choice, a 2N3055 and PNP complement have been used for audio amplifiers output devices for many decades. The best site I've come across for audio circuits and articles (the articles have a lot of educational value) is the Elliot site:

**broken link removed**

PS: And the prior poster is most correct in stating the power transformer, at these power levels, will be the major cost of the project and will have to be considered carefully to see if it fits into your class or student's budgets. Lowering the power level to say 20 watts or under might make all the difference. Also don't forget about heat-sink requirements for the output devices. This is often unstated in design circuits, but if ignored will lead to quick failures. While that can be very educational also, I suspect that you would wish for a more positive educational experience for you students.

Lefty

 

[audioguru]

I have a hifi FM stereo receiver that is about 44 years old. It uses two 2N3055 transistors in its output for each channel in a quasi-complimentary circuit. Its output power is 18W into 8 ohms but could be up to 40W per channel with a higher supply voltage (55V).
Its distortion is not too bad at about 0.3% at low frequencies and about 2% at high frequencies where I can't hear the harmonics anyway.

In Google there are many circuits for amplifiers that use the old 2N3055 transistors.

 

[Hero999]

I agree with kchriste, the transistors are cheap compared to the price of the transformer.

Get hold of a 24VAC control panel transformer - you can probably get one second hand or from a scrap yard for next to nothing.

To get 100W from it you'll either need a bridge or a voltage doubler to get + and - supplies.