The everyday use of a tube amp

well this is completely different, but similar questions have been asked regarding projector bulb usage. One poster replied that he services projector, and someone came in with a projector that had 7000 hours on the bulb before it blew. This is an unheard of number of hours. When he asked the owner how he got so many hours, the guy said he simply woke up in the morning, turned on the projector, then turned it off before he went to bed. So at least for bulbs, the on/off cycles seem to be the killer, not necessarily the number of hours on.

I would not wait for a tube to completely stop functioning before replacing it. Tubes can get dull sounding and still function. I have had this experience. Some tubes in a particular design may be more critical than others. The manufacturer may be able to tell you which. This happens with video CRT tubes also. Users wil be happy with a CRT for years, until one gets replaced and it is much brighter than all the others. They lose brightness over the years, but so slowly, you don't realize it. The net result si that when you own tubes, you end up constantly wondering if your system is going dull, and when it's time to re-tube.

Many amplifiers (Audio Research comes to mind) have a stand-by switch that cuts plate voltage when you're not listening but don't want to actually shut down the system. They also recommend you don't leave the amp in stand-by indefinately ;-) but it's a good way to keep the amp warmed up and ready to go all day without unnecessarily using a lot of AC (and a lot of A/C ;-)

If the amp doesn't have the stand-by option, I feel a happy compromise is to restrict on/off to AM/PM as some already mentioned, and maybe once during the day if one has to leave for an hour or more (never NEVER leave tube gear going in an empty house!) If you would have to shut down and warm up your system more often than that during the day, you probably won't have time for quality listening anyway. Why put mileage on the power tubes and burn up electricity for background music? -- isn't that why SS integrateds were invented?
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I have the Dodd Mono 50s (which I love) and often run them 10 hours a day. They are a Class A/B design with a standby switch and they do not run particularly hot.

The tubes used are very inexpensive: the output tubes (of which there are only two total) are widely available at $10-20 apiece and the drivers (four total) are about the same ($10-15).

According to Gary Dodd, the tubes should last five years or more with "ordinary" use. I would imagine that would mean about 1000-1500 hours/yr. so you'd need to replace them around once a year with your usage. Definitely change them before they burn out as you could lose a fuse and resistor, or worse, if not. In any event, as a poster above noted, the sound will deteriorate before the tubes give out.

Good luck and enjoy,

Rob