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At power on tube filaments light up more than normal for a sec
"flipper" wrote in message ... On Tue, 09 Dec 2008 09:14:29 GMT, Patrick Turner wrote: flipper wrote: On Tue, 09 Dec 2008 07:19:16 GMT, Patrick Turner wrote: Phil Allison wrote: "Arny Krueger" Electricity flows at the speed of light, ** ROTFL !! But heat travels down a wire at the speed of a sick snail. and the whole tube is in a vacuum. ** Yeah - vacuums are real *******s, they really suck. The thermal intertia of the components the filament contacts would be a possible variable. ** Hey - no fooling. Amazing how everyone has already thought of that !!!! Most tubes that have separate and symmetrical sides are are duals, and they seem to light up about the same. ** My god - that is an inspired insight ...... There might be far less flash at the tops of tubes because the filament wires are just barely poking out, while the ones at the bottom run all the way down to the pins. ** IME - there are those that are " top flashers " and there are those that are " bottom flashers ". And I am speaking of tubes, not people. ...... Phil Phil, looks like I was right. Not quite. I posted the same quote and while it's probably sufficient to allay the concerns of a home user it's not technically correct. For example, the description that "So in effect one side of the tube always warms up 1st" makes no sense. It also seems he got a bit confused with the heater wiring. Remember, a 12AX7 has a center tapped heater and it appears to me that he confused the two going to pins 4 and 5 as 'one side' with the one going to pin 9 as the 'other side'. At any rate, I did look at mine and it's simply that the insulation doesn't extend all the way to the pin weld so a portion of the bare filament is exposed. His explanation for the flash is also incomplete. It isn't just the "very little resistance." It's the lower thermal mass of the uninsulated segment that warms faster than the rest so it's resistance increases faster and causes more voltage drop across it, increasing the power dissipated in that segment, till the remainder of the heater warms to operating temperature. I seriously doubt that 50-75 mils out of the entire heater length has a significant effect on the overall surge and the instantaneous initial peak would still be the same since the 'whole thing' starts off cold. The surge lasts a much shorter time if part of the heater or an additional link installed is allowed to glow like a lamp filament at turn on. Actually, if it had any effect, which is doubtful because of the minuscule section affected, the surge would last longer because it would 'limit' (sic) the power input, so the rest would take longer to heat. Just what the makers did to get the flash is not clear until someone provides evidence of exactly how it was done. I suggest someone smash open an old flasher and see what's inside. I'm too busy with orders for new amplifiers. I already told you I *looked* and it's nothing more than the last few mills of the heater wire having no insulation. Which illustrates the danger of allowing a hypothesis to inform an observation, rather than vice-versa. If Patrick's initial answer were correct, and if there is a seperate link of special wire in series with the heater, then it could look just like you have seen. What you can not see by your inspection is your "nothing more than". How do you know that the rest of the heater wire is the same as what you see? How do you know that you are not looking at the "special link"? I am quite happy to accept that some flashers depend on an exposed length of heater wire which is otherwise identical to and continuous with the rest. But not on the basis of your woefully inadequate observations. And to establish that they are *all* like that would take more than observation, practically. You would need intelligence. Ian |
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