The All Japanese Six Radio.

Conclusions.

There are no dangerous voltages in an AJ6 so stick your fingers in there as much as you want. The transistors are not MOS (Metal Oxide Semiconductor) so you don't need to worry about static electricity. However, the transistors are germanium which has a lower melting point than silicon. These transistors can be damaged by too much heat applied with the soldering iron.

If you are thinking "why not replace them with silicon", for get about it. The design of the base biasing networks takes into account the steady state base to emitter voltage drop. For germanium transistors this is approximately 0.1 volt. For silicon the base emitter drop is approximately 0.6 volts. If you replaced all transistors with silicon the radio very probably would never work again. There are on line companies who sell PNP germanium transistors for hobbyist who want to restore a pre-silicon transistor radio.

There are many more variations on the AJ6 theme than the two shown here. The circuit never became as standardized as the AA5 tube radio was. I think a large part of the reason is that when manufactures settled on 6 transistors as the best compromise between cost and performance the transistor was not nearly as mature as the tube was when 5 was found to be the magic number for cost effective radio sets.

Nonetheless extensive study of these pages and the additional diagrams found at this website should arm you with sufficient knowledge to restore any old pocket or table model transistor radio that falls onto your workbench.

General Information.
The Converter.
The IF (Intermediate Frequency) Amplifier.
The Detector and AGC/AVC (Automatic Gain Control/Automatic Volume Control).
The Audio Amplifier Section.
Conclusions.

This page last updated April 25, 2011.