preamp tube flash

[hellaboogie]

I have a preamp tube that briefly flashes when powering on, the amplifier operates properly, anyone ever experience this, is it safe to continue using the tube in question.

 

[Tonelover]

Yeah, me too. I asked the guy who made my amp and although I don't remember his reasons, it's normal and nothing to worry about.

 

[2tallmusic]

this is normal behaviour of e.g. Matsushita and some Philips-family brands AFAIR like Amperex etc.

More a quality attribute then an issue.

 

[charveldan]

Normal ... as long as it doesn't catch fire ur golden.

 

[Shark Diver]

Normal ... as long as it doesn't catch fire ur golden.

That's reassuring

 

[hellaboogie]

Strange, of all the preamp tubes I've ever had, this is the only one that I seen flash

 

[glip22]

Strange, of all the preamp tubes I've ever had, this is the only one that I seen flash

Its just gas. Perfectly normal.

 

[just42dave]

means its a good tube trust me....

 

[hellaboogie]

right on thanks

 

[Tonelover]

Here's what I found online from www.tubefreak.com

Have you ever noticed how some tubes like new old stock Mullard or Amperex 12AX7s "flash" brightly when you turn on the power? The answer is rather technical so bear with me. The two filaments have unequal cold resistances. When power is first applied, the filament with the lower resistance passes more voltage over to the other filament, which makes it glow brightly (Ohm's Law at work). As the lower voltage filament warms up, its resistance rises to the hot resistance of the other filament, allowing both to get equal voltages. This effect is pronounced in amplifiers with AC filament supplies because larger amounts of current are available for the tubes, DC filament supplies light those found in better hi-fi equipment tend to be current limited, reducing the opportunity to "flash."

 

[baron55]

Besides the old NOS Amperex and Mullards, the Chinese tubes seem to do this quite a bit.

Groove Tubes actually tried to use this phenomenon to validate there 12AX7M (Mullard re-issue) "Flashes like the real thing, so it must be good" LOL

 

[Anonymous]

it's about to burn out. trust me.

i'll buy it for 3$ though....i like those ones in my old radio......

 

[steve_k]

Most NOS tubes do this, especially, EI's, Mullards, RFT's, etc. Nothing wrong with it.

 

[Anonymous]

Most NOS tubes do this, especially, EI's, Mullards, RFT's, etc. Nothing wrong with it.

shhhhh!

 

[rockify]

means its a good tube trust me....

My nos tubes do this, newer production tubes I noticed do not.

By the sound of it ^ what he said

 

[just42dave]

all my ei and mullards amperex etc rft do this gas and voltage = good tube made well others are junk sell them all to me for cheap

 

[Hail Satin]

Put it in a vox ac 30.

That way, when it catches fire you'll have more than enough reasons as to why it went up in flames...