# Why is the voltage across collector and emitter pushing itself to 0.7 volts?

I designed a single stage transistor amplifier as shown in this schematic:

I constructed this on a breadboard and applied the DC bias voltage to check the biasing conditions. Prior to this, I made the following assumptions: 1. The collector current ( also almost equal to emitter current) is 2mA. 2. The small signal gain of the transistor is 100. 3. The collector to emitter saturation voltage is 0.2V.

Now with these assumptions, I calculated the resistor values Rc and Re. As per my analysis, I had predicted that the voltage drop across Rc, Rc and Vce would be 3V. But in practice, when I measured the DC voltages, I found the voltage across Rc to be 4.1V, that across emitter was 4.2 volts and the voltage Vce was 0.7 volts.

This meant that the transistor was being driven into saturation and when I connected to a speaker, the output was attenuated rather than amplification. Where did I go wrong in my analysis?

• I think your biasing voltage is too high. Try replacing R2 with a 20K pot. then test with the pot in a few diff. positions to see if you can get a desirable respose. Commented Jan 30, 2016 at 6:48
• I tried this now. The result is the same. Vce remains at 0.7V
– Sâu
Commented Jan 30, 2016 at 6:53
• With R2 turned down to 0, Vce should have jumped to almost 9V Commented Jan 30, 2016 at 6:57
• He's saying that with R2 turned down to zero the base voltage should drop to zero, and the transistor will turn off. The emitter voltage should then drop to zero and the collector voltage go to 9 V. Report back on Vb, Ve and Vc with R2 turned down to zero. It sounds as though R2 isn't connected properly. Add photo of breadboard to original post. Commented Jan 30, 2016 at 8:10
• Double-check that you have connected the transistor correctly. It's easy to get it wrong and Vce=0.7V sounds suspiciously like Vbe or Vbc for a forward biassed diode.
– user16324
Commented Jan 30, 2016 at 12:51