TRANSISTOR
MUSEUM ™ Historic Transistor
Construction Project |
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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 |