Trouble prototyping an AB amplifier

[kilwan]

I was given a project in college to calculate, simulate and prototype an AB amplifier. My calculations match the multisim simulation. Now the last step I needed to do was prototyping the circuit. I made the circuit on a breadboard and went to the college lab.

So here is the circuit:
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And here is the breadboard:
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**broken link removed**

I should have gotten something like Vce1=15V and Vce2=15V
I got Vce1= 9V and can't really remember Vce2.
I used two DC sources that have (+),(GND) and (-) ports. For the input I used a function generator with (+) and (-) ports. Now I didn't even get to adding the function generator since my DC measurements weren't correct, so there really was no point in trying to do AC measurements. I hoped you guys had some tips on what to do, since I'm at a total loss here. I checked all of the connection, all of the resistors can handle the power .... Maybe I created a short somewhere ? Maybe I hooked up the DC source wrong to get the negative voltage I need ?

Would really appreciate some input

 

[deepmak]

Hello Kilwan
have you tried connecting the load resistor R3 to the output via a decoupling capacitor ? most probably your circuit is drawing much Quiescent current
also test voltage drop on both diodes and BE of the transistors , the idea of diode biasing is that those voltage drops are identical , if not , try with other diodes
also the signal input should be connected to the circuit via decoupling capacitor
hope this helps
Regards

 

[E-design]

You have an imbalance in the idling current of the two transistors, or they are biased on too much. Try to change the circuit as below and monitor the voltage drop over R1/2 while adjusting R6. They should be the same. In this case, 15.5 mA is flowing through both (with no signal input). You don't want this current too high as to overheat your transistors. Try to keep it under 25 mA. R1/2 will also help with thermal stability and to reduce distortion. The transistors need to go on a heat sink if you are going to test full-power output of your amp. Furthermore, D1/2 should preferably be thermally coupled to their respective transistor for thermal compensation.