Tubes at idle

I would always turn off amps that are not going to be used for a long time. First, for safety reasons, the amps should not be left completely unattended for long periods. Second, heat will, to some extent, shorten the life of the other non-tube components, such as capacitors and resistors. Third, he cathode of the tube, which emits the electrons, have a limited capacity to do so which is wasted at idle; most preamp tubes are not run really hard so they have a pretty long life, but, given the cost of decent tubes, it makes sense to not waste them; also, some designs actually run preamp/linestage tubes pretty hard, so that tube life may actually be as short as one-year, so conservation really makes sense there. Finally, it makes little sense wasting electricity as heat from running gear unnecessarily (tube gear is works inefficiently as space heaters).

The reason that one might have for leaving gear on is that it does sound better when fully warmed up and stablized at full operating temperature. The good news for tube fans is the gear actually warms up pretty fast, compared to solid state stuff, so that most gear sounds very good within 10 minutes or so of turn-on. If your listening habits involve frequent short-term interruptions, that might be a reason not to turn the gear off and on at every interruption.

I know there are those who are concerned about shortened tube life from the "surge" at turn. The analogy is to how light bulbs rarely fail in the middle of use; they almost always fail at the instant of turn on. With tubes, this is somewhat different. Bulbs are designed to come on instantly--when the filament is cold, it conducts so easily that the surge at turn-on causes abrupt temperature changes that causes the old, weakened filament to fail. This is, to some extent true for tubes as well, but, they actually light more slowly and do not suffer as much from thermal shock.

To the extent there still is some concern with turn-on stress to tubes, different equipment design has an impact on this as well. Gear that uses tube rectification in the power supply inherently turn on more gently. The rectifier ramps up the current/voltage to the rest of the gear instead of creating an instant-on situation. Some gear may also include circuit elements designed to ramp things up slowly, such as thermistors in the power feed that slowly increase current flow as they heat up, or circuits that don't allow the plate voltage to be at full strength until the cathod/heater are fully heated (if the plate tries to pull electrons from the cathode before the cathode is heated and readily delivering electrons, damage can occur to the cathode ("cathode stripping"). These turn-on issues are usually bigger issues with power amps than with preamp/linestages.

I don't think actual fire is a common event, but, then again how much is even a small risk? If replacement tubes are cheap, the only other major cost to consider is the amount of electricity the component burns at idle (some manufacturers give buys that figure). You have to decide for yourself whether the environmental issues matter to you. If the amp remains reasonably cool, then heat degradation of other components will not be that big an issue.

The only real advantage to keeping the preamp on all the time is the issue of warmup--that can be a big deal if you don't have time to wait or really dislike the sound of your system while it is warming up. I would at least listen to my system to decide whether warmup is that big a deal or not; I would not rely on consensus opinion on the internet.

For my own gear, I must turn it off to conserve the tubes because none of them are that cheap. My linestage runs four 310s and two 311s, plus a rectifier. My amp runs four 348s and four 349s (even more expensive than the linestage tubes). My phonostage runs two 300Bs as rectifiers, two tubes that I cannot recall the type (reasonably cheap) and two ECC803S tubes (quite expensive).

Tom,

Thanks for interesting link to Sears Sound. I know that the primary concern in this discussion is the impact on the tubes, but, Sears Sound also mentioned the issue of heat impacting other components. That is also a concern that I have. Every manufacturer's specification sheet for parts, such as resistors and capacitors, includes an estimate of the lifespan of the component; this rating is not a single figure but one that relates lifespan to the operating temperature--the higher the temperature the shorter the working life of the component.

In an earlier post, I suggested that tube rectification provides a form of "soft start" for the rest of the downstream tubes. I should say that this is probably NOT as good at providing protection as a true soft start circuit. My linestage has an outboard power supply with a tube rectifier and an unbilical to the main unit. On turn on, even with tube rectification, there is a huge voltage spike (the main unit has a meter) and then voltage drops to the normal operating range. During this time, a circuit with a relay protects sensitive parts of the main unit.

One other word of caution. If you have to turn tube gear off and then plan to turn it back on again almost immediately, it is better to wait a few minutes rather than waiting only a few seconds. I have noticed that some gear will behave rather badly when turned back on quickly. This can take the form of making loud noises through the speaker and/or tubes emitting a bright flash of light (particularly the rectifier); I don't know how much harm this does, but, it cannot be good.