Elenco 130-in-1 Electronics Playground - Manual (Page 152)

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The twin-T type audio oscillator is very popular for
use with electronic organs and electronic test
equipment because it is very stable.
The resistors and capacitors in the twin-T network
determine the frequency of oscillation. The letter T is
used because the resistors and capacitors are
arranged in the shape of the letter T in the schematic
diagram. There are two T networks in parallel across
from each other; hence the term twin is used. The
capacitors in series shift the phase of the wave; the
resistors in series supply voltage to the transistor’s
base as well as shifting the phase of the wave.
Carefully adjust the circuit to obtain pure sine wave
output as in the previous two projects. Modify the
control very slowly over its entire range until you hear
a tone in the earphone that is very low and resembles
the lowest note of a large pipe organ. This control
setting should be between 7 and 10 on your dial.
Once the oscillation has started, adjust the control
carefully for the setting that gives the purest sounding
low note near the high end of the dial.
You can experiment with this circuit in many ways. We
suggest you try different values for the 10k
Ω and
470
Ω resistors, and try using higher and lower battery
voltages. Also, if you have a VOM, try measuring
circuit voltages.
Notes:
EXPERIMENT #130 TWIN-T OSCILLATOR
Schematic
Wiring Sequence:
72-106-116-27-124
28-104-102
46-103-87
47-101-86-81-EARPHONE
48-71
119-115-82-EARPHONE
85-88-105
121-122