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Filament Flash in K-12G (10GV8)
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=6499
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Author:  Xolotl [ 01 Apr 2019, 11:31 ]
Post subject:  Filament Flash in K-12G (10GV8)

Hi Guys

I recently saw this video:
https://www.youtube.com/watch?v=bX0o3jAzSBs&t
He says he experienced shorter lifespan due to filament flash when working for a large company, and that they overcome this problem placing a resistor in series with the heater and a switch parallel to the resistor, turning this one on after the current consumption has settled.

I am planning to make a case for my K-12G amplifier, and have been thinking of adding this modification to the heaters.
Do you think this is a good idea? Have you experienced problems or a shorter lifespan on your tubes because of this reason? What kind of resistor should I use, given the total current consumption for all four heaters would be 24w?

I also investigated a little bit about the heater wiring, but I understood (correct me if am wrong) that this is more to eliminate hum, rather than eliminating filament flash.

Thanks guys!

Author:  gofar99 [ 01 Apr 2019, 17:44 ]
Post subject:  Re: Filament Flash in K-12G (10GV8)

Hi, I have not had tube life shortened by the start up flash. It seems that some individual tubes are more prone to this than others, but the life does not seem to be compromised. Some individual tubes are not made consistently and a small part of the filament is exposed (most are nearly completely covered by the cathode) and it will seem to flash worse than others. That is harmless. In a commercial set up with numerous on-off cycles flashing might matter as you need high reliability. For home audio I would not bother. I use those tubes and similar ones and they seem to last forever.

Good listening
Bruce

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