Reflex and regenerative circuits are combined in this sensitive
and stable radio.
B1-15·volt battery (two Eveready
404E's or . equivalent in parallel)
capacitor (Lafayette MS-445 or equivalent)
miniature electrolytic capacitor C3-30-µf., 25-volt miniature
electrolytic capacitor C4-.0005-µf., ceramic capacitor
C6-Gimmick capacitor (see text)
L1-Antenna coil for C1 (Superex 2004 or equivalent)
L2-Six turns of #26 insulated wire wound on L1 (see text)
All resistors 1/4 watt
control with s.p.s.t. switch S1 (Lafayette VC-28 or equivalent)
S1-S.p.s.t. switch (on R4)
T1-Coupling transformer (Philco
32-4763-2 or equivalent-see text) 1-2000-ohm impedance earphone
(Lafayette MS-368 or equivalent)
1-4" x 2 1/2" x 3/4" plastic box
1-4" x 2 1/2" x 1/16" phenolic
Misc.-Tuning dial, knob for volume control, wire,
One transistor does the work of two in this highly efficient
circuit. The signal is amplified twice-once at radio frequencies
,and, after detection, at audio frequencies.
HOW IT WORKS
One transistor and
one diode are employed in a circuit that combines the advantages
of both reflex and regenerative action. Because the signal passes
through transistor Q1 twice - once as r. f. and once as a.f.
- the transistor is properly described as operating in a "reflex"
circuit. Adding to the already high efficiency of this circuit
is the regeneration furnished by gimmick capacitor C6.
In operation, the r.f. signal picked up by antenna coil
L1 is tuned by coil-capacitor combination L1-C1 and induced
into secondary coil L2. Fed directly into the base of transistor
Q1, the r.f. signal is amplified and passed to transformer T1.
A portion of the signal from Q1's collector is returned to Q1's
base by capacitor C6 to provide additional gain through regeneration
, The signal induced in T1's secondary is detected by diode
D1, smoothed by capacitor C5, and returned to the base of Q1
through volume-control R4 and coupling capacitor C2.
Transistor Q1 again amplifies the signal, this time at audio
frequencies. The audio signal from Q1's collector is fed through
the primary of T1 to the earphone.