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Old 4th Jan 2021, 10:30 pm   #2
Radio Wrangler
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Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Default Re: Help with a transistor id please

THey look to be 'house numbers' literally stock numbers used by an equipment manufacturer.

7831 and 7904 are likely to be date codes Year 79 (1979) and week 04 for example.

The most likely manufacturers are RCA and Motorola. A good photo might let that guess be refined a bit more. There are style details in the moulding and even the typeface that can be give aways.

Failing that, given the circuit diagram, some reverse engineering can be done and suitable devices suggested.

In transistor amplifiers it is unfortunately common for one failed transistor to take a number of others with it. If you try replacing one at a time, the dead ones take out the new ones and you can get locked in an infinite circle.

The escape from this is to test them all and replace all faulty ones without applying power until they've all been changed.

It takes a bit od self-discipline to go the long way round, but it's a lot quicker than a short-cut

David
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