Historic Transistor Construction Project  



This is the schematic for the modern point contact transistor audio preamplifier.   Here are some comments from the designer of this unique circuit, Gerry Friton, who spent many hours and brought to bear considerable electrical engineering expertise to contend with the characteristics of the “tempermental” point contact transistors:


“ The amp has a gain of around 25 max, highly dependent on bias settings (phase of the moon, what you ate this morning, etc) – these point contact trannies almost beat me!  I used a common emitter configuration, more as a challenge than anything else – common base is more usual.  You know, I didn’t think there would be so much interest in point contact technology. Amazing!” 


I have used the preamp for the past two years and have had no problems.  The unit is activated when the earphone is plugged in and the original batteries are still good.  I have been able to use a cable to connect the output of the preamp directly to the “MIC” input of my computer sound card and record the audio.  Clearly not “HiFi”. There is a unique character to the audio produced by this historic device - best described as a slight “sizzle”.   It is likely that these sounds haven’t been widely heard in almost 50 years and provide a real tribute to the first transistors!


Copyright © 2002 by Jack Ward