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TRANSISTOR
MUSEUM ™ Historic Transistor
Construction Project Valandy 1950s Code Oscillator Kit |
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This
is the schematic for the Valandy oscillator.
It is a Colpitts oscillator,
in which the earphone is the inductance tuned by the two capacitors. The transistor is operated in common base
mode, and the circuit is very similar to its vacuum tube “cousins” from the
same timeframe. |
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To
the left is a closeup view of the top of the oscillator. Note the CK718
transistor, which has been socket mounted.
The two capacitors, shown in the center, are also of the same 1950s vintage
as the original Valandy kit – modern caps could be used instead. |
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There are
several aspects of building this modern version of the Valandy kit which you
should keep in mind. Most germanium
PNP transistors should work, although the very early types, like the CK718,
may need to be selected. Since the
earphone inductance is a critical part of the circuit, it is important to use
a high impedance (2000 ohm) magnetic type, as shown in the photos on pages 1
and 3. Finally, if you use a CD case,
or similar base for building and displaying your oscillator, be careful when
drilling the holes for the screws to mount the components – this type of
plastic is very brittle and cracks easily. Go
To Valandy Code Oscillator Project - Page 3 |
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Copyright
© 2003 by Jack Ward |
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