10W Class AB Amplifier - Further Development Results

To test the conventional 9:1 transformer I blogged here I revised the board. The populated board is shown below:

With scars of many replacement transistors

I started with a 2SC1306, a once common CB output transistor. The smoke escaped all too quickly. I then tried a few general purpose transistors with unsatisfactory results.

One of the key things I noticed was that as the output was increased many transistors had a threshold. When that threshold was exceeded the output quickly dropped. If the bias was too high then thermal runaway also occurred.

The presence of this self-heating effect was noted in all of the transistors I tested, sometimes resulting in transistor failure. TO220 packages were better than TO126 packages presumably because they have a lower thermal resistance.

With only a few 2SC1306 left I switched to a 2SC2146. I was able to get close to 4W (40Vpp) but  eventually the smoke escaped.

I'm going to replace the transistor and see if a larger transformer is needed. 

73's

Richard