Tube Life

I see no reason whatever to leave a preamp on all the time, unless the unit is solid state. if you have expensive rare tubes (e.g., the TFKs you guys are discussing), why let them go to waste when you are not even getting the fun out of them? It is true that there is some stress on a tube at turn-on, but that can be ameliorated by a "soft-start" circuit and by only applying plate voltage after the filaments have warmed up (which takes only about 10-20 seconds for 9-pin miniature triodes like 12AX7). Both of these goals are easily achieved by any thoughtful designer. Most tube units will be in "full song" within 20 minutes or so after turn-on. (So will I.) When a tube ages, it loses "gain" and input sensitivity. Thus the report that the sound gets flabby or dull or lifeless makes perfect sense and is a good guide to tube replacement.

In contrast, SS units are not at their best unless or until operating temperatures have stabilized, which can take hours. Since SS devices are at even greater risk than tubes at turn-on, and since their lifespan is much longer than that of a tube. it does make sense to leave SS gear on at all times.

Lewn, I aqree totally with you. I don't see any reason to leave tube gear on all the time. Most sound very good within a pretty short time after being turned on, while solid state gear can take hours to come up to full song.

Concerns about the thermal shock at turn on are over exaggerated. When cold, the filament will conduct more readily so that there is a quick in-rush of current and rapid heating at turn on. But, with tube filaments, this does not happen with the kind of speed and severity of something like a light bulb.

In any case, all my tube gear use tube rectification, so the signal tubes are protected from instant on conditions--it takes a while before the rectifier is putting out full current so it acts like a soft-start circuit.

Depends on the voltage how high.DUDE!!

Right, a tube rectifier helps to protect the downstream tubes from simultaneous application of filament and plate voltages. The plate voltages will come up slowly. Also the simple use of a thermistor in the filament transformer primaries will protect both the transformer and the tubes from rapid application of filament current. Most modern gear, even including tube gear, uses SS rectification and so does not afford the natural protection of a tube rectifier. However, it is a simple matter to employ a relay device that effects a time delay between application of filament voltage (first) and plate voltage (second).

I would not want to have to go hunting for ECC803S TFKs on an annual basis.

Having an extra reference set to compare to is the best way to know for sure how another set is performing.

Or else you might just trust your ears enough to detect a problem that matters when it sneeks in.