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EARLY SEMICONDUCTOR
AUDIO
As the GE Semiconductor Applications
Engineer specializing in audio/HiFi circuits, Dwight Jones worked with
rapidly evolving technology in the 1950s and 1960s. In the photo above, the 2N167 on the
left is one of the earliest transistors to be used in an audio circuit by
Dwight. This device is a crudely
constructed grown junction germanium transistor from the mid 1950s and is
shown in the earliest GE Transistor Manuals in both radio and audio
applications. On the far right is a
prototype of a silicon monolithic diffused IC device developed by GE in the
late 1960s. Dwight developed Application Notes on this line of consumer
audio devices, which were marketed as the PA (Power Amplifier) series. The PA 237, for example, was a Two Watt
audio amplifier containing seven transistors; it was intended to be used in
consumer products such as TVs and radios.
The 2N508 (second from left) was used extensively by Dwight in his
early transistor HiFi designs. This
device was introduced by GE in the late 1950s and is a germanium alloy
junction transistor. According to
Dwight “The 2N508 was one of my favorite early transistors. It had
relatively high gain and low noise.
I used it a lot for audio projects”. The three unmarked devices in the center of the photo are
all GE prototype silicon transistors from the 1960s which Dwight evaluated
for HiFi usage. The silver
can-style unit was marketed as type 2N2107 – it is a silicon diffused unit
designed as a medium power audio output transistor. The remaining two units in the photo
(both with heatsinks) are prototypes of the D40 series of late 1960s
silicon NPN audio power transistors.
The 15 year timeframe from the mid 1950s to the late 1960s shown in
the photo above illustrates the dramatic changes in audio semiconductor
technology that occurred during Dwight’s
career.
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In the July 1959 edition of Electronics World
magazine, Dwight Jones published an article on an all solid-state stereo tape
amplifier. This was pioneering work
and represents some of the earliest published material for true HiFi caliber
transistorized magnetic tape amplifiers.
Dwight developed several versions of this circuitry, which appeared in
various 1950s and 1960s publications, including Electronics World, Journal of
the Society of Audio Engineering, and editions Four through Seven of the GE
Transistor Manual. The circuit board
shown above is a commercialized example of these important applications
developed by Dwight – this board is the circuitry for one channel of a stereo
tape amplifier. There are four 2N508
germanium transistors in the preamp section (one silver and three black units
shown on the right). The power output
is provided by silicon diffused silicon 2N2107 style units (one is shown with
finned heatsink in the upper left of the board).
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Go
To Jones Oral History, Page 5
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