startup glowing

[catalin gramada]

Hello.
I found some of my triodes , no matter new or used, glowing at startup. It was happen even with a current limiter on power supply. Every unit tested in circuit shows no functional issues. So, why is happen that? It is a reason to worry about,please? Thanks

[Enzo]

I hope they all glow, as the heaters must be glowing for the tubes to work. If you mean some of them flare brightly at first, that is normal for some tubes.

[catalin gramada]

Thanks. Yes some flare brightly for sec at startup.
That.s weird

[Zozobra]

Are they being used as a cathode follower?

[catalin gramada]

Are they being used as a cathode follower?

one of section is used in AC coupled cathodyne inverter. but I tested some in regular voltage amp rc coupled stage and is same phenomen. some goes brightly some not even same type from same lot. That.s very annoying. I did.t have the curiosity to test all my stock tubes till now. What can be cause of this ?

[J M Fahey]

YOU shouldnīt be annoyed by a perfectly normal phenomenon.
Since one "problem" of Tubes is that they they take 30 to 60 seconds to heat up to normal temperature, so no "instant on" like SS components, (as a side note thatīs one reason Standby switches were invented: filaments were kept always ON, only +V was switched ON-OFF) , so Tube makers invented some weird filament wire alloy which heated up real fast, and then kept desired temperature, so *visibly* they get hot in a few seconds (so they "flashed" for a second) , thatīs what you see .

[Leo_Gnardo]

FWIW Amperex dual triodes, the typical ECC83/12AX7 and similar, tend to flash white on starting up. It only lasts a small fraction of a second and does not seem to harm the tubes. Instead they're highly sought after. We have better things to be annoyed at, right?