tube question

guitarteck · 07-15-2009, 11:00 PM

Hi
I have a 75 50 watt jmp that was recently serviced when i take off the back and turned it on I notice the 2nd 12ax7 flashes bright right away then is fine. is that normal?

T-Bird · 07-16-2009, 12:19 AM

Hi.

That's sometimes a sign of a gassy tube and that can lead to a failure. An untested new tube that's "lit" for the first time can burn also something that is visible.

BUT...

I have a NOS Mullard which has done that for about one and a half years now without any problems. Used to scare the crap out of the drummer in our band

.

Regards
Sam

guitarteck · 07-16-2009, 12:48 AM

funny you mentioned that 1st tube was a mullard but still did it with the groove tube

MartyStrat54 · 07-18-2009, 10:45 PM

There are several brands of tubes that "flash" when first turned on and it is normal. Usually they are Mullard or Amperex tubes. There are a few others. If you have a tube that is current prodction, then you would have to consider getting the tube tested. I'm not familiar with any current made tube that has the heater flash. Could be signs of a problem.

Marty

07-15-2009, 11:00 PM	#1 (permalink)
guitarteck Junior Member Join Date: Jul 2009 Posts: 5	tube question Hi I have a 75 50 watt jmp that was recently serviced when i take off the back and turned it on I notice the 2nd 12ax7 flashes bright right away then is fine. is that normal?

07-16-2009, 12:19 AM	#2 (permalink)
T-Bird Senior Member Join Date: Jul 2009 Location: Finland (Northern Europe) Posts: 214	Re: tube question Hi. That's sometimes a sign of a gassy tube and that can lead to a failure. An untested new tube that's "lit" for the first time can burn also something that is visible. BUT... I have a NOS Mullard which has done that for about one and a half years now without any problems. Used to scare the crap out of the drummer in our band . Regards Sam

07-16-2009, 12:48 AM	#3 (permalink)
guitarteck Junior Member Join Date: Jul 2009 Posts: 5	Re: tube question funny you mentioned that 1st tube was a mullard but still did it with the groove tube

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