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Old 9th January 2007, 04:41 AM   #1
arnoldc is offline arnoldc  Philippines
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Default Weird crackling sound without B+ applied

Hi,

Over two nights I made a simple UL EL34 amplifier. I don't have a schematic now, but the driver section is a 1/2 5687 with 10mA diyAudio CCS on the plate, 750R (bypassed) on the cathode to give ~8V bias, cap coupled to EL34 with 1K series on the grid and 220K grid resistor. The UL tap of the transformer is connected to the EL34 G2 via 1K resistor. 470R (bypassed) on the cathode of the EL34 to give 20V bias.

The power supply is a simple full-wave with FR107 -> 470uF -> 500R 10W -> 470uF and I installed a switch (on the negative leg) for standby.

When power is applied, but no B+ (standby on), there's crackling sound coming from the speakers. When B+ is applied, it goes away and the amp is playing well.

Any thoughts? I'm sorry but this is the first time I have experienced such.
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Old 9th January 2007, 07:54 AM   #2
EC8010 is offline EC8010  United Kingdom
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Arcing across your (open) standby switch.
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Old 9th January 2007, 09:51 AM   #3
arnoldc is offline arnoldc  Philippines
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Ooooh! My bad...

Thanks!
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Old 9th January 2007, 10:02 AM   #4
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You're welcome.
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