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

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>
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.
</pedant>

Cheers

Ian
.

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