Enough next to your telephone to put a small plastic box, as from the speaker there is a loud voice. The secret here is simple: mounted in the box coil (scheme) “detects” the electrical signals of the phone conversation, coming then a three-stage transistor amplifier with low frequency.
Coil L1 and ULF are linked by a two-meter shielded cable. The sensitivity of the device is adjusted by potentiometer R1.
L1 contains 1250 turns of wire PEL of 0.1—0.15, is wound in several layers on a ferrite rod Ф600 (Ø 10 mm, length 140 mm). The transistors T1, T2 — МП39 — МП42, T3 — МГІ20, TP1 — output transformer from a pocket radio, Гр1 — compact loudspeaker type 0,5 GD-17, GD of 0.5-20.
Recommend to read
FURY WITH A SPANISH ACCENT
Fighter biplane Hawker FURY. The first third of the century of aviation, leading the countdown from the flight of the Wright brothers in 1903, can be called the era of biplanes. Most of...
“FALSHSTENA” WITH A DOORWAY
Many citizens in the Soviet Union had to pass through the panel, "building", built in the second half of the last century. These homes are designed for 50 years of operation, will...
