...even when you turn off the "power " switch you can still see the tube filaments staying lit. I suspect this may be why it tends to wear out tubes...
It
shouldn't be. Generally speaking, when a tube "wears out", it loses cathode emission (long before the filament burns out). I'm not saying it doesn't happen, but I've used
hundreds of tubes and can count on one hand the number of filaments that I've seen die.
Allen, when your tubes "go", do they stop
glowing?
Or does the tube still glow, but not produce good sound any more?
Tmazz, I suspect that – (if your filaments
are burning out) – it's due to a less-than-optimally-designed power supply. I would try putting an ICL (Inrush Current Limiter) in series with your filament, such as this one:
http://www.digikey.com/product-search/en?pv679=87&k=inrush+current+limiter&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=500These are
passive current-limiting devices and will not have
any negative effect on the sound; (if anything, it will sound
better, as current-regulated filament supplies tend to do). They can get quite hot though, so make sure it's in a well-ventillated location.
But it will do two things for you:
1 – Limit the "cold filament" inrush current; when the filament's cold, it has about ¼ of it's running resistance and therefore draws a lot more current. This is probably the biggest cause of filaments burning out — (which is probably why your AI chooses
not to switch them on and off).
2 – Keep the power supply from delivering too much voltage and/or current (and prolong the life of the tube).
You
should be able to leave the tube(s) on 24/7 and, if anything, the cathode emission will fall off long before the filament burns out. (BTW, the cathode emission isn't affected when there's no power to the anode — hence the power switch).
