It is always recommended to turn the volume down before turning the preamp (any) off. A small light click from the Candela when turning off the unit is not an issue and should not be a concern. Of more concern would be a loud thump at turn-on mainly from older solid state amps.
Regarding tube life on small signal (preamp) tubes is very much dependant among other factors, on how “hard” the tube is running in terms of total tube dissipation measured as “Wmax”. The Candela preamp circuit as designed runs the ECC82/12AU7 tubes very conservative at 36% of total tube capacity, very light indeed. In this specific case tube life expectancy should be long. In general terms and adding my own personal experience close to forty years using tubes, dramatic failure normally occurs in the first (or less) hour of operation that in my view would be indicative of poor circuit design and/or tube manufacturing quality control. In over 300 plus JJ’s tubes used so far I have seen only “one” tube failed and caught of course within the initial testing and burn-in time.
For the record, the original “Candela” prototype preamp has been mostly on (JJ tubes) close to four years now, or 30,000 plus hours! A couple months ago I tested these tubes in my tube analyzer (please read tube analyzer ant not tube tester), and they were still measuring at over 90%!!
Now, keep in mind that like a light bulb a vacuum tube can go anytime…chances are that a good quality tube should last a long time in the “mighty Candela preamp”. Food for thought… aa
Thank you,
Alex
