Help! My EL34B based amp arced at full volume. - diyAudio
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Old 26th August 2012, 04:01 PM   #1
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Default Help! My EL34B based amp arced at full volume.

My 2 year old EL34B based amp arced on the right channel for the first time. I was measuring the db output with my little dbmeter I was about 10 feet away. I heard one static crackle, one of the EL34B tubes on the right channel arced between two pins in the front of the tube. I was not close enough to see what pins they were. But close enough to see the arc then the bottom of the EL34B glow brightly for a second. I was close enough to shut down right away. I am driving 4 ohms speakers off the 4 ohm taps. Everything was sounding great at 90db. After two minutes I turned the amp on again and listened at 30% volume. Sound is fine, bias voltage is fine on all 4 EL34B tubes. I listened for 30 minutes, no arcs and the EL34B apperars to be operating normally. I have a 1/16" gap between the bottom of the final output tubes and the sockets. Should I force the tubes to be flush with the sockets ?

Have an of you seen this before ? I used to see this when a cap is failing on an old tube radio, but when it started arcing it didn't stop until I replaced a dead capacitor and rectifier tube. My 55w EL34B amp stopped arcing as soon I lowered the output volume and input signal level.
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Old 26th August 2012, 04:45 PM   #2
DF96 is offline DF96  England
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Valves should usually be fully inserted into their sockets, to ensure good contact. It is possible that you have seen the effect of parasitic oscillation.
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Old 27th August 2012, 02:32 AM   #3
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I've been listening to tunes through my el34 based amp with the wife. Volume is at 30%
. Its been 1hr now and no problems. It still sounds great!
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