Quote:
Originally Posted by stonehopper
what an AF11x problem is!
Darren (or Steve) - how can I check the polarity? Will it have toasted everything if wrong?
Cheers - Derek
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Your radio have all the signs of either short circuit output transistors because of the overheating output transformer or the battery connected the wrong way round, and as you have had it connected for long enough to get things warm, if it is the latter then it may have damaged transistors in any case. But the previous owner would have done the same if a battery had been connected wrong.
To find out which way the battery should be connected look at the diagram and either find a large value electrolytic capacitor with the positive side shown and trace this back to the positive battery lead. Or trace the Emitters of the PNP transistors back to the printed circuit via the Emitter resistors of each transistor and this is where the positive side of the battery should go, usually via the on/off switch. The negative side of the battery to the negative side of the electrolytic.
Mullard produced a germanium transistor range with the AF designate such as AF114 AF115 AF116 AF117 that obviated the need for external negative feedback capacitors and resistors to neutralise the self capacitance of earlier transistors like the Mullard OC44 OC45 and the transistors where very good when new. But they had two flaws that led to failures, first the screening lead could break internally and short out the base connection, and more seriously the metal used in the case construction causes fine metal ‘whiskers’ to grow and eventually come into contact with the semiconductor and short out the electrodes to the case.
Geof