What Does It Mean When A Tube Flares?

[Eastside]

When I turn on my Tram D201....one of the tubes flares up bright at the bottom....then goes back to normal....it tests good on my tube checker....simple output test.

 

[wavrider]

the way you describe it the tube may be getting to much heater voltage when you first turn it on, thus the bright flare up but once the voltage settles down it is normal

 

[Eastside]

Did it on the tube checker also.

 

[DainBramage]

not sure what tubes are in a 201,.but,.........Many European tubes in the 12AU7, 12AT7, and 12AX7 families may flash brightly when you first power up your gear.
This flash is normal. It is also normal for the intensity of the flash to vary from tube to tube, and the flash intensity may also vary or even go away as the tubes age.

 

[Eastside]

Thanks....DB

 

[Beetle]

Sitting turned off for a while, the filament gets cold, and its resistance decreases to a pretty low value. When the equipment is turned on cold, the current sees a low-resistance path through the filament circuit and charges ahead, heating the filament in a matter of a second or two and raising its resistance to where it's designed to be. It sounds brutal, but unless you have something like the Harbach soft start system to bring the filament voltage up in steps, it's gonna happen. Apparently, the tubes are, and have been for decades, able to withstand the sudden application of full filament voltage with no harm done.

 

[Eastside]

Thanks for explaining that Beetle.