Filament of a 6AS7G

[GF]

I am theoretically examining the behaviour of the filament of a 6AS7G tube during a slow turn-on.
I'd like to know the current into the filament for some applied voltages. I only know the current when the filament is completely cold and when it's completely hot.
By chance, do you know such data? Or do you know a right approach to the question?

GF

[Ryssen]

I only know the current when the filament is completely cold and when it's completely hot.

How do you know this values,how much is the differnce cold and warm,interessted to know.

Isn´t it possible to messaure it with a multimeter?

[EC8010]

If you look at pages 269-271 of "Valve Ampifiers" 3rd Ed. Morgan Jones, you will find a full test methodology and results that should answer your question.

[fdegrove]

Hi,

I am theoretically examining the behaviour of the filament of a 6AS7G tube during a slow turn-on.

I've always been a little curious what a lightbulb would be like if it had the same coated heater with controlled warm up....
Would it come up slower. Would the bulb last longer?

Cheers,

[EC8010]

My understanding is that thorium was added to the tungsten filament in lightbulbs to make it more ductile (more easily drawn through the die to form the fine filament wire) and that increased emission was a secondary effect. I've seen valves that flash like light lightbulbs at switch-on (to reduce warm-up time), but I've never seen any that are deliberately slow. Conversely, the only lightbulbs that are slow are the ones with thick filaments. As a kid, we found that it was a waste of time connecting the sound-to-light* stage effects unit to 500W lamps, but it was very effective when connected it to a batten carrying a dozen 60W domestic bulbs.

* We bought the sound-to-light (with school money) as a ready-built PCB, put it in a box, and connected it to the mains. It blew up once (we overloaded it) but we replaced the triacs. All as school kids...

[fdegrove]

Hi,

I've seen valves that flash like light lightbulbs at switch-on (to reduce warm-up time), but I've never seen any that are deliberately slow.

Slow is quite likely the wrong word, "controlled" warm up they called it.
Remember the "A" suffix on US small signal valves?
Apparently this A was to indicate the presence of such a coated heater.
Whether it was actually slower, I very much doubt. The main reason I think was to appease users as they were worried by the flash as it resembled a miniature lighting show inside their table radios when switched on.
They were probable convinced something was wrong with the valves...

The reason is simple, what you see is actually a part of the heater sticking out of the cathode sleeve. If you coat that part away it won't be visible anymore and everyone's happy.

It blew up once (we overloaded it) but we replaced the triacs. All as school kids...

Hmmm...I build my own too...With a few triacs of course and colourful 100W spots.
All hanging from the ceiling at my parents loft which I occupied during adolescence and gradually turned into a mini disco.

Cheers,

[EC8010]

Originally posted by fdegrove
Remember the "A" suffix on US small signal valves?

Strictly, the "A" suffix meant the first type development of the original valve, although I agree it often meant "controlled warm-up". Contolled warm-up was needed by televisions (which used series heater strings connected directly across the mains) in order to avoid the weakest link in the series chain from being overloaded at switch-on.

Hmmm...I built my own too...With a few triacs of course and colourful 100W spots.

I'm delighted to have proof that there were other hooligans. I did all sorts of things that are considered to be un-PC now, but never quite managed to blow myself up.

[GF]

Originally posted by ryssen


How do you know this values,how much is the differnce cold and warm,interessted to know.

Isn´t it possible to messaure it with a multimeter?

First of all I must correct my words. I only know the RESISTANCE of the filament when it's completely cold and when it's completely hot, so I only know the inrush current and the current at nominal voltage (2.5A@6.3V).

Ryssen,
I wrote "I am theoretically examining" to say that I don't own that tube so I can't perform measurements.

GF