Really bright flash below the bottom mica when I turn my amp on?
Nov 21, 2008 at 5:01 AM Thread Starter Post #1 of 10

olblueyez

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Ok guys, anyone know what it means when there is a really bright flash below the bottom mica when I turn my amp on? Its the input tube and its only the one tube. The tube works fine, no noise and sounds great. Whats it all about?
 
Nov 21, 2008 at 1:03 PM Post #2 of 10

sacd lover

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Quote:

Originally Posted by olblueyez /img/forum/go_quote.gif
Ok guys, anyone know what it means when there is a really bright flash below the bottom mica when I turn my amp on? Its the input tube and its only the one tube. The tube works fine, no noise and sounds great. Whats it all about?


Some European tubes are known to do that .... and that behavoir is normal. I have some 6V6s that do that and they have worked for a couple years now with no issues.
 
Nov 21, 2008 at 1:18 PM Post #3 of 10

atbglenn

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My parent's old 1960's Harmon Kardon receiver's pre-amp tubes used to glow very brightly at the base when you first powered it up. If I remember correctly, the tubes were never replaced in all the years they had it.
 
Nov 21, 2008 at 1:24 PM Post #4 of 10

Rob N

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Is the flash white?
As SACDlover said some tube heaters glow very bright on switch then this subsides
 
Nov 21, 2008 at 4:27 PM Post #5 of 10

Golden Monkey

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My Woo's tubes do the same, to varying degrees. My Siemens 7308 do it the most - just a power-up flare-up, then they fade completely, then they slowly brighten up over a minute or so. Seems they only do this once...if the amp has been off for a while, it does it when first turned on. If you turn it right back off for a minute or so, and turn it back on, no surge-y flash, just a slow brightening.
 
Nov 21, 2008 at 7:46 PM Post #7 of 10

Pricklely Peete

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Some Amperex tubes are known for that flash at initial power up. I have a quad of 12AX7's labeled Electrohome but are genuine Amperex with that cool flash when the power switch is toggled on
smily_headphones1.gif


The flash should only last a second or two and settle right away.

Peete.
 
Nov 21, 2008 at 10:52 PM Post #9 of 10

mackman

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A lot of conducting metals have a much lower resistance at room temperature and can heat up rapidly when the power is turned on. Once they reach operating temperature the resistance increases, current drops, and they cool back down. That's why light bulbs always seem to burn out when you first turn them on.
 

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