Amplifiers at the workbench

I decided to go back and revisit a simple Class AB amplifier circuit based upon an NPN and PNP bipolar junction transistor that I worked on a couple of weeks ago. I am not sure what happened but I lost the magic and was not able to reproduce the gain in the circuit. <sigh>

After a bunch of messing around I grabbed a prototype Class A amplifier circuit board that I built back in February 2010. (It is even on an etched board)

The circuit is not very efficient since I am using about 190mA of current @ 12vdc. It is very much a Class A circuit with small signal parts but it has some gain. (The extra resistors are tweaks that I made 20 months ago to tweak the bias.)

If current is not a concern then this is generating 250-400mW of power with the RF drive that I would expect from a AD9851 DDS. Since I am using plastic NPN parts I have a heatsink on the final transistor (it was pretty warm to the touch.)

When time permits I will need to come back and design a new set of gain stages that are more efficient. Class A is a simple but expensive way to generator power. I need to think about Class B or Class C stages.

73 de NG0R