VEF 206 Schematic

The VEF 206 circuit diagram shows that someone extremely skilled and talented in radio engineering designed this radio. The circuit is highly optimised and the ten transistors and two diodes provide the best performance.

Here is a list of transistors used in the main stages of this radio.

• Π422 IF amplifier
• Π423 heterodyne oscillator
• Π423 Mixer
• Π423 HF amplifier
• MΠ40 AGC
• MΠ41A LF amplifier

My friend Alexander told me that these transistor packages are commonly known as hats.

Band Selector Circuit

The circuits between contacts 1 – 8, and 9 – 16 are located on the band switch drum. When the drum rotates, a different circuit, specific for each band, connects between those contact points.

The ferrite rod consists of coils L11, L12, L13, L14, L15, and the band switch contacts 1,2,3,4,5,6,7,8 connect to the ferrite coils in different configurations forming different circuits. Band switch contacts 9, 10, 11, 12, 13, 14, 15, and16 connect a dedicated slug tuned circuit on the rotating drum, to the local oscillator circuit consisting of transistor T1 (Π423) on the PCB. Each tuned circuit sets the oscillator frequency for a specific band.

Audio Power Output

The audio power output stage begins at transistor T8 (MΠ41A), which drives a phase splitting transformer Tr1. The opposing phases of the audio signal emerge on the secondary of this transformer, each driving their respective transistors T9, and T10. These transistors are usually a matched pair and can be a pair of MΠ40, or a pair of MΠ41. The output of these transistors feeds transformer Tr2, which recombines the opposing phases of audio in the secondary, whilst the primary drives a loudspeaker. When the audio is fuzzy and low volume, it usually points to a faulty output transistor, because half phase audio usually sounds fuzzy.

This Article Continues...