National Panasonic T-100D Circuit

Looking at the printed circuit board components the first stage transistor appears to be a 2SA70. There are also two 2SA101 transistors each at the first and second intermediate frequency (IF) stages. It also has those ancient OA70 diodes, which are extremely large, and usually provide detection for the automatic gain control (AGC).

The audio frequency (AF) stages consist of 2SB173 transistors, which behave as preamplifiers to increase the signal strength to a sufficient level to drive the 2SB175. The transistor at this stage drives the primary winding of a phase splitting transformer, which usually has a centre-tapped winding on the secondary side. Each side of the centre tap consists of opposing phases of the audio signal that feeds the base junction of the power output transistors, which in this build consists of a matched pair of 2SB324 transistors.

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