Re: At power on tube filaments light up more than normal for a sec

Ian wrote:

Actually, in a conductor electricity does not 'flow at the
speed of light' the net flow of electrons in a conductor
is barely a few meters per second.

Two different things, depending on what you think
electricity is. Flow of electricity happens much faster than
your surely quaint "net flow of electrons".

Speed of light is not a great help, either, considering
light may be considered to flow at different speeds, and
doesn't flow at all in a heater wire.

Arny would have been better off just saying it's really
fast, or near-as-dammit instantaneous, and leave light out
of it altogether.

There is something in what he says, in that "thermal
inertia" cannot alone explain flashing. For a one-part
heater, electrical inertia would be necessary, such as a
choke. Since it happens without a choke or other source of
electrical delay, there must be two parts to the heater.

Ian

"Ian Bell" <ruffrecords@xxxxxxxxx> wrote in message
news:ghjhra$295$1@xxxxxxxxxxxxxxxxxxxxxxxx
Arny Krueger wrote:
"flipper" <flipper@xxxxxxxx> wrote in message
news:tv2qj41a6c2vdveo579pelmeq8290fptfm@xxxxxxx

Well, I found this explanation.

http://reviews.ebay.com/Why-Mullard-Amperex-12AX7-flash-when-1st-energized_W0QQugidZ10000000002972031

That jives with what my first guess was. That a small
bit
of filament was 'bare' while the rest is sort of
heatsinked inside the cathode section so the 'bare' part
flashes as the rest warms up slower. That would make it
just an artifact of their particular construction
technique.

Seem questionable:

"The "flash" is perfectly normal and it's a trademark
characteristic of Mullard / Amperex tubes. There are a
couple other brands that have a similar flash but I'll
discuss Mullard / Amperex tubes specifically since they
are my store specialty."

IME the flash was very common in the Japanese equipment
that Lafayette used to import, back in the day of. Now,
the Japanese may have been building tubes using
Mullard/Amperex technology, but it was mostly the U.S.
brand tubes that *didn't* flash.

"The flash occurs on one side of the filament wires
between the bottom plate and the inside bottom of the
tube and this phenomenon only occurs when powering up
from a cold start. The sudden influx of current on the
cold heater filament encounters very little resistance
along this wire (hence the sudden burst of light). So in
effect one side of the tube always warms up 1st, the
second takes a while to catch up but before long the heat
is evenly distributed (and your amp comes to life). "

Electricity flows at the speed of light,

<pedant>
</pedant>

Cheers

Ian


.

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