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Old 25th August 2005, 01:49 PM   #1
Sherman is offline Sherman  United States
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Talking Cool Fireworks (tubes are tough!)

I decided to use tube rectification for the EL84 amp I just built because I had a couple of Chinese 5U4-Gs on the shelf. They were there because when I had them installed in my KT88 amps they flashed on startup. I put in Sovteks and the flash went away.

Anyway, I finished soldering up the amp and tested the voltages without tubes. I then put in the 5U4-G and when I powered it on there was a flash of light in the tube and then a shower of sparks inside the envelope like a miniature fireworks display. Very cool-looking and not very upsetting because I sort of expected issues with those tubes. After a couple seconds the 2A Slo-blo fuse blew ending the fireworks display.

I re-checked all my solder joints, redid one that tested OK but looked grainy and disconnected the CT on the 5V secondary. I replaced the fuse and powered on again. Guess what? No sparks, no flashing just a slow warmup and B+ voltage right where it should be!

Holy cow tubes are tough suckers! (Even those cheap Chinese ones.)
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Old 25th August 2005, 05:41 PM   #2
karma is offline karma  Canada
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heh ya i did that one time by shorting the rectifier tube by mistake


the down side is it shortens the tubes life
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Old 25th August 2005, 05:48 PM   #3
Magura is offline Magura  Denmark
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Quote:
Originally posted by karma

the down side is it shortens the tubes life

Hmm, had it been a solid state device the life would have been shortened dramatically, as in the time between the flash and the bang


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Old 25th August 2005, 09:32 PM   #4
Sherman is offline Sherman  United States
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Quote:
Originally posted by Magura



Hmm, had it been a solid state device the life would have been shortened dramatically, as in the time between the flash and the bang


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I suspect that the glass envelope of tubes helps hold in the magic smoke!
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