CLASSIC 1950s ARTICLES ON EARLY TRANSISTOR AUDIO AND HOBBYIST APPLICATIONS

An Interview with Paul Penfield Jr.

 

Oral History – Paul Penfield Jr.

(Continued)

 

What are your recollections about your first involvement with transistors?

 

In grade school and junior high, I was really interested in electronics.  You know, making crystal sets and things like that.  This was before transistors.  My first recollection of the transistor was in 1947, when it was invented at Bell Labs.  I was freshman in high school then (in Birmingham Michigan, where I grew up).  I confidently predicted to my friends that this would never amount to anything because it had no filament, and therefore no source of power.  I’ve since been proven wrong (laughing).  My other concern was that this was based on point contact technology and I understood how fragile this was, so part of my not paying attention had to do with the fact that they were point contact transistors, and I knew they could not be rugged enough for practical applications – which turned out to be the case.

 

What made it revolutionary was when Shockley published the theory of the junction transistor and suddenly people realized that this was robust and clearly something that could be made in quantity.  By that time, I knew more about transistors and solid state, so I could appreciate it.  That must have been in 1951.  I was in college at Amherst (Massachusetts), majoring in Physics and still had my interests as a hobbyist in electronics.  I could see that the junction transistor was

 

 

 

 

Oral History – Paul Penfield Jr.

(Continued)

 

something I had to pay attention to.  I tried to translate all my knowledge about vacuum tube devices and circuits into transistors, and it went fairly smoothly.

 

Please provide some background about your first published transistor article.

 

At this time in college, I was the chief engineer at our college radio station - WAMF.  Basically, I was the only engineer, because no one else cared about hacking with electronics. I decided that what we needed more than anything else was a remote amplifier.  This is a preamp which you attach to a microphone to boost the signal up to a large enough level (a few volts) so that you could transmit by wire  from one place on campus to another.  We strung wires from our building to every other building on campus.  There was no “wireless stuff” back then.  We got down in the steam tunnels and took our wires everywhere. This worked out pretty well, but then we needed preamps to be able to use remote pickups.  So, I decided that what we needed was a transistorized remote; I made one in the summer of 1953 with some CK721 transistors.  Because power transistors weren’t available, I had to use a tube for the output stage.  It had two or three transistors.   As I recall, it even had two microphone inputs, one for the interviewer and one for the interviewee, so you wouldn’t have to share a microphone.  

 

Go To Penfield Oral History, Page 3

 

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