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Old 23rd September 2004, 07:53 AM   #1
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Default What happens if I loose the cathode bias?

I have been thinking about using LEDs to bias a single tube transformer coupled 12B4A linestage. I suppose that the failure rate of LEDs is higher than for a resistor. What happens if the cathode suddenly loses the connection to ground?
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Old 23rd September 2004, 08:09 AM   #2
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What happens if the cathode suddenly loses the connection to ground?
Nothing at all. Just no sound.
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Old 23rd September 2004, 01:14 PM   #3
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If the cathode is bypassed with a low voltage, large value electrolytic, you'll hear a loud BANG!
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Old 23rd September 2004, 03:44 PM   #4
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Thank you for the input guys :-)
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Old 23rd September 2004, 06:15 PM   #5
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Well, I had one valve (EL34) in a P-P circuit operating without the cathode resistor for a couple of hours before I noticed it - the prominent lack of emission glow alerted me to the fact! The amplifier still sounded just fine though, using the other half of the P-P circuitry. No damage occurred, but it is not something I like doing...

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