Re: so we will have to install a filament standby switch ...

j0k3335 · Post by **j0k3335** » Mon Dec 07, 2020 2:49 pm

I find this on YT :

?

his channel is interesting for dummy like me ( he even knows the Capacitor Outside Foil ...

)

JustMike · Post by **JustMike** » Mon Dec 07, 2020 5:18 pm

I guess the condensed version is; "Don't use crappy European tubes like Mullard, Telefunken and Amperex".

Post by **pompeiisneaks** » Mon Dec 07, 2020 5:36 pm

He had to search a lot and found almost nothing about a very serious problem that almost nobody knows about?

His videos can be informative, but they are really really long. In my mind often 3x longer than they need to be.

That and adding in this kind of odd drama he seems to be trying to drum up are pretty weird too.

~Phil

Charlie Wilson · Post by **Charlie Wilson** » Mon Dec 07, 2020 5:40 pm

How is this specifically Dumble related?
CW

Post by **Colossal** » Mon Dec 07, 2020 5:49 pm

Charlie Wilson wrote: ↑Mon Dec 07, 2020 5:40 pm How is this specifically Dumble related?
CW

Maybe move out to Technical Discussion?

Post by **pompeiisneaks** » Mon Dec 07, 2020 5:59 pm

Yeah didn't catch that myself. Moved to the right place.

~Phil

turbofeedus · Post by **turbofeedus** » Mon Dec 07, 2020 6:27 pm

Hmm the video gives some straightforward solutions, and hints at the problem. But it doesn't really explain why filament flash occurs in some tubes, and not others.
We know that tungsten wire has a positive temperature coefficient of resistance, meaning the resistance of the wire increases as the temperature increases.
This explains why the wire draws so much current at startup, and slowly tapers off to around 300mA (for standard preamp tubes)
But that's true for both flashing and non-flashing tubes, so it seems that's only a correlation.
So what is the actual cause of the flash? I noticed the flash or hot spot was created at a tight bend in the filament wire, and also seemingly where the wire meets the coating. Perhaps these factors are involved?

Post by **pompeiisneaks** » Mon Dec 07, 2020 6:40 pm

turbofeedus wrote: ↑Mon Dec 07, 2020 6:27 pm Hmm the video gives some straightforward solutions, and hints at the problem. But it doesn't really explain why filament flash occurs in some tubes, and not others.
We know that tungsten wire has a positive temperature coefficient of resistance, meaning the resistance of the wire increases as the temperature increases.
This explains why the wire draws so much current at startup, and slowly tapers off to around 300mA (for standard preamp tubes)
But that's true for both flashing and non-flashing tubes, so it seems that's only a correlation.
So what is the actual cause of the flash? I noticed the flash or hot spot was created at a tight bend in the filament wire, and also seemingly where the wire meets the coating. Perhaps these factors are involved?

I think a more important question is "how often does filament flash happen to tubes"

I'd wager it's extremely rare. It's like a solution seeking a problem.

~Phil

mhuss · Post by **mhuss** » Mon Dec 07, 2020 7:18 pm

No consumer-grade tube is designed to need a gradual application of heater voltage. They are designed to handle the initial cold surge. Due to design? materials? coatings? some tube heaters flash when power is applied, and most don't.

turbofeedus · Post by **turbofeedus** » Mon Dec 07, 2020 7:41 pm

mhuss wrote: ↑Mon Dec 07, 2020 7:18 pm No consumer-grade tube is designed to need a gradual application of heater voltage. They are designed to handle the initial cold surge. Due to design? materials? coatings? some tube heaters flash when power is applied, and most don't.

And yet, according to the claim in the video, tubes were failing "in numbers" due to heater flash. Is that true? Maybe, maybe not.
Seems like a reasonable thing to at least understand, if for no other reason than the pursuit of understanding itself.

TUBEDUDE · Post by **TUBEDUDE** » Tue Dec 08, 2020 1:03 pm

Is this really an issue? I've used Mullards and Telefunkens for decades and have had 0 failures. They flash every turn on but haven't failed. Several have been in builds over fourty years old. And most were ANOS when I got them.

Phil_S · Post by **Phil_S** » Tue Dec 08, 2020 1:49 pm

turbofeedus wrote: ↑Mon Dec 07, 2020 7:41 pm And yet, according to the claim in the video, tubes were failing "in numbers" due to heater flash. Is that true? Maybe, maybe not.
Seems like a reasonable thing to at least understand, if for no other reason than the pursuit of understanding itself.

Listen carefully. I believe, when he mentions failing in large numbers, he is not talking about 12AX7's and that sort of tube. He talks of "big tubes," maybe some sort of broadcasting tubes? I suspect he has generalized without basis in fact.

BTW, that guy needs more equipment. Let's send him all of our spare stuff to be sure he has enough.

professormudd · Post by **professormudd** » Tue Dec 08, 2020 2:04 pm

That guy reminds me of Scott Thompson from kids in the hall.

turbofeedus · Post by **turbofeedus** » Tue Dec 08, 2020 5:26 pm

Phil_S wrote: ↑Tue Dec 08, 2020 1:49 pm
turbofeedus wrote: ↑Mon Dec 07, 2020 7:41 pm And yet, according to the claim in the video, tubes were failing "in numbers" due to heater flash. Is that true? Maybe, maybe not.
Seems like a reasonable thing to at least understand, if for no other reason than the pursuit of understanding itself.
Listen carefully. I believe, when he mentions failing in large numbers, he is not talking about 12AX7's and that sort of tube. He talks of "big tubes," maybe some sort of broadcasting tubes? I suspect he has generalized without basis in fact.

BTW, that guy needs more equipment. Let's send him all of our spare stuff to be sure he has enough.

The example shown in the video of filament flash is a 12xx7 tube however. So it's not as if it doesn't happen at all in that style tube.
It probably doesn't lead to mass failure, otherwise it would be talked about more. But that doesn't mean it's not worth at least investigating, which is what I'm primarily interested in.

professormudd · Post by **professormudd** » Tue Dec 08, 2020 6:57 pm

Would it be worth keeping an eye out for filament flash as an indicator that you have a tube that is gonna have a shorter life?