Two NPN transistors pull-push amplifier explanation please, also does transformer cause phase shift too?

Question

I was trying to build AM receiver. First thing, I got sound out without a detector circuit. I think I may know answer for that: that is my common base amplifier (the one I used at the input just after the tank circuit) was also acting like a detector. After two more amplifier stages, I still could not get enough to run speaker. It was running small ear phone though. I am trying to make pull-push amplifier by using two NPN power transistors coupled with transformer. I do not have PNP power transistor.

I got the circuit for two NPN transformer coupled amplifier from an old book, but my problem is I do not get how this circuit works.

Answer 1

You cannot do push pull with just npn or pnp.  You can get some other kind of amplifier, but not push pull.

I think your problem is coupling.  Make sure you are capacitively coupled and the amplifiers are class A.

Answer 2

yes, you can use a transformer and two NPNs to drive a speaker. You will need a phase splitter to drive the NPNs, a npn with equal emitter and collector resistors will do that, with E and C coupled with caps to the two NPN output stages.

You must have a correctly designed transformer for this. I'd guess at about 200 ohms center tapped to 4 ohms. But that is a guess.

But as I understand it you only need a watt or 2 to drive a small 4 ohm speaker. A simple class A single stage amp will do that much easier.

Edit: sorry Warren, but think back to the tube days. There was no pnp vacuum tube, they came in one polarity only. Pushpull amps used a phase splitter, two power tubes and a transformer to couple the two phases of the tubes to the low impedance speaker.