Power cycling, tube life, and audio quality

[Fredo]

Hi, folks:

I'm listening to my Mainline and enjoying the heck out of it. I burned it in for about 100 hours playing sequentially into two headphones (one planar). It initially sounded a little raspy and distorted, but that pretty much went away.

Anyway, my question is whether to power the unit off (mainly at night) or leave it on. With older high-end commercial transistor amps, the rule of thumb was to leave them on in order to stabilize temperature and sound quality. The same might apply to the Mainline.

Thermal stress resulting from power cycling could shorten tube and component life, but leaving the amp on could also shorten tube life.

Thoughts and recommendations?

Thanks,

Fred

[Doc B.]

Turn it off. Start it up about 20 minutes before you want to listen.

[Fredo]

Hi, Doc:

Thanks for your reply. So the advice is to turn it off at night - will do.

What about a more frequent duty cycle: turn it on at 9am, listen for two hours while working, turn it off for two hours, turn it on for two hours, and then turn off for the night? Would it be better to leave on for 8 hours during the day?

Cheers,

Fred

[Doc B.]

It's not like a light bulb. The tube typically dies from depleting the cathode material over time with use, not from thermal cycling. That said, tubes can certainly fail for different reasons, shorts, gas, dropping something heavy on them, etc. The most certain way to keep from using up a tube is to switch to transistors.

[drewh1]

here is some info from the EML site about burning in tubes.

Yes they do! Good Burn-in will assure maximum lifetime and develop the final sound. These tubes are burned-in initially, to do the factory testing, after tube data becomes stabile. However emission of the cathode is not homogenous at this moment. Emission is build by many small islands, overlapping each other. This will not give the final sound yet. The burn-in process will take place in the first 50-100 hours under normal use conditions. This means it is best to switch off the amplifier after each use, and in the beginning not use the tubes longer than 4 hours at one time. Many short use periods have a better result than few long periods. The tubes need the „cold“ periods in between for best formatting of the filament. Some blue glow effect on the glass will disappear during burn-in, or may take longer to disappear eventually. What you observe, is a fluorescent effect, and it is normal with new tubes, even so proving cleanliness of the glass. For good burn in, use different loudness levels from the beginning, and increase the maximum loudness gradually. If tubes with very little use were switched off longer than 12...24 months, it may be necessary to repeat the burn in. So tubes that were not used for some years, may sound unpleasant, and simply need a new burn in.

[Fredo]

Thank you both for your replies. It appears that I should have burned in the tubes with more power cycles.

Anyway, onward!

Thanks again.

Fred

[drewh1]

According to Jac at EMI - you can still sort of "recondition" tubes that have had certain types of problems by going through the power cycling process, so it might not be too late!