Recently acquired, this B302 was built in 1977, and has been
stored for a long time in slightly damp conditions,
and some corrosion has affected it.
The intention is not to make it look like new, but get it running safely
and reliably, keeping as many of the original parts as possible.
These were originally designed as high quality PA amps, maybe a competitor
to the Amcron DC300 which it outwardly resembles. At 100W per channel
it is far too feeble for a modern PA system, but it is
a suitable power amp for hifi.
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Internally looks fairly OK, but a lot of the diodes seem to have cracked in half. |
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Output transistors test OK, but very rusty and will be replaced. |
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Fortunately the transformer is working well, I baked it to dry it out as a precaution, but there was no evidence of internal problems. The capacitors still hold charge well, but are leaking electrolyte and will be replaced. |
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One of the original Turner branded transistors. |
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Assessment of the boards shows that three small transistors, the bias trimmer, two electrolytic capacitors, one resistor and all eight 1N4003 diodes need replacing. |
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A few of the failed diodes. They seem to have cracked in half. |
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Replaced capacitor. |
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First repaired board fitted for testing. |
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Both boards in place. |
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Front panel fitted. |
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First volts out for decades. This scope is a Gould Advance OS250B, which is actually a few years older than the amp. I think I looked after it a bit better though. |
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Click for schematic |