Elenco Electronic Playground 50-in-1 Experiments - Manual (Page 29)

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Look again at the water pipe analogy for the transistor,
the lever pivot: What would happen if the base and collector were
connected together? Once there is enough pressure to
overcome the spring in check valve DE (0.7V) there
would be only slight resistance and no current gain. This
situation should sound familiar since this is exactly how a
diode operates. When the base and collector of a
transistor are connected together the transistor becomes
a diode.
Connect the wires according to the Wiring Checklist and
press the switch, the LED lights. This is the same circuit
as Experiment 11, One-Way Current. This demonstrates
how transistors can be substituted for diodes, and this will
occur in practice sometimes for manufacturing reasons.
EXPERIMENT #15: The Substitute
Wiring Checklist:
o 27-to-56
o 55-to-16-to-15
o 17-to-42
o 43-to-3
o 4-to-26
Schematic