I have a Zenith Royal 500 DeLuxe pocket radio that I just aquired, it turns on and works, but one of the transistors gets hot, and as it does the volume decreases. Cooling off the transistor by using a screwdriver as a heatsink or by turning the radio off and letting it cool down returns the volume back to normal. Do you guys think it is a problem with the transistor, or could it be a surrounding component that is causing it? Is it normal for it to get hot? None of the other transistors seem to get hot.
The easiest thing I could think of is swapping transistors if there is another one on it. If the other transistor behaves the same way you know it is surrounding circuitry. If it follows, get a new transistor. Otherwise, it could be biased incorrectly causing the heating. Voltage measurements could provide some insight on what it is being provided.
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