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Old 26th July 2002, 12:21 AM   #1
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Unhappy BJT subject to hum?

Are Switching-intended BJTs likely to be subject for hum, per a chance?
at least thats what i suspect, ive built a 20W range amplifier in class A, and the delivery with my 'real' BJTs for my project hasn't arrived yet, so, for testing purposes i took a pair of swithing BJTs, (2SC4060) and 'voila' the amp works (woks..), but with a awful hum, i tested at slightly lower bias with regular BJTs and...there was no hum...strange!?.. -or maybe not very strange?
..maybe i have to re-engineer my psu, its a standard non-regulated, 500VA toroidal and a capacitor bank@60,000F, i do think that should be sufficient...
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Old 26th July 2002, 02:58 AM   #2
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Hey! I've played with 2SC4060's but only for switching, not linear. Switching BJT's have a relatively poor safe operating area compared to one specifically meant for linear, but they would switch *much faster*. That said, is your amplifier oscillating? Stick a scope on and have a look. Maybe the higher speed capability of the '4060 has upset the stability somewhere?

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Old 26th July 2002, 10:52 AM   #3
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No, theres no oscillation...now i have the 'real' Transistors, and it sounds marvelous, no hum at all.
...but i do still wonder why there was hum with the 2SC4060...admit that's strange!?
well, what the heck, now it works anyhow!

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Old 26th July 2002, 01:44 PM   #4
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Hi Mr. Triatic

I don't have the datasheet of these transistors at hand but could it be that their beta is significantly lower (specially with the bias you are using) than the beta of your "real" transistors ?.

Regards

Charles
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Old 27th July 2002, 12:20 AM   #5
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jep, that might be the case, it would have been fun to really know what was happening there, but what the heck...
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