B1-15·volt battery (two Eveready 404E's or . equivalent in parallel)
C1-365·µµf. variable capacitor (Lafayette MS-445 or equivalent)
C2-10-µf., 25-volt miniature electrolytic capacitor C3-30-µf., 25-volt miniature electrolytic capacitor C4-.0005-µf., ceramic capacitor
C5-.01-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)
R2-22,000 ohms All resistors 1/4 watt
R4-10,000-ohm volume 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 board
Misc.-Tuning dial, knob for volume control, wire, solder, etc.
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.