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Old 2nd April 2011, 05:42 PM   #1
ryuji is offline ryuji  United States
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Default Leave it on or turn it off?

I imagine this isn't a cut and dry answer. I have been operating my 807 pentode power tube and 12au7 pre and 12at7 driver tubes continuously for about a month now. If there was any 'burn in' to happen. its done. i have additionally wired a 'standby' switch which disconnects my pentodes from ground, disrupting all current through them which helps to power on the amp a bit softer and additionally gives me a way to not have to turn off the amp when i get up to leave for a break/etc.

My question is: now that i am pretty sure i have burned in all of my components, when i say, head off to work for the day or go to bed/etc. should i cut the main power to the amp and shutdown/cool down all components for the sake of tube life/power consumption/thermal concerns. Do i gain something in sound for having tubes that have been running for weeks without a break? If turning on/off has no effect other then the warmup time and some hard to measure filament life decay i think just from an ecological/thermal point of view especially since summer is approaching, Im best turning it off. But if there are significant effects of doing such i might consider keeping the heaters running.
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Old 2nd April 2011, 06:06 PM   #2
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"My question is: now that i am pretty sure i have burned in all of my components, when i say, head off to work for the day or go to bed/etc. should i cut the main power to the amp."
YES.
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Old 2nd April 2011, 06:27 PM   #3
ryuji is offline ryuji  United States
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There is nearly always someone around in my house, and i have all my transformers fused to blow if there is any kind of short. but, yea, for the first two weeks i was careful to be around when the amp was running should something go wrong. But on the other hand filaments running is no worse then leaving some light bulbs running. that is more so what im wondering at this point. ill be powering off my power transformer and adding some protection with relays for runaway situations, such as losing my fixed bias, just havent got around to buying the relays for it yet
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Old 2nd April 2011, 07:39 PM   #4
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I saw an equation for tube life 30 years ago, it had something for hours on. Something about the paint on the cathode losing the ability to boil off electrons. None of my tubes in my ST70 or PAS2 has ever burned out the heater. They go low bias current on the output tubes, or low output voltage on the rectifier, which I tend to blame on not enough electrons coming off the cathode. The 12AX7's in the PAS2 get where they draw too much current and the B+ is low, which I blame on gas leaking in (over 60 years, 3 of 4 are 1961 tubes). My Mother's 1954 Philco TV, yes, filaments went out.
So I vote for turning it off once a day. I always did, running my rigs all evening most days, and the big tubes would wear out in about 8-10 years.
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Last edited by indianajo; 2nd April 2011 at 07:42 PM.
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Old 2nd April 2011, 07:44 PM   #5
ryuji is offline ryuji  United States
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cool, then from your experience turning them off once or twice a day doesn't hurt them at all when it comes to practical lifetime, especially as i have spare tubes, in fact you seem to be saying it will make them last longer.
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Old 2nd April 2011, 07:51 PM   #6
bigwill is offline bigwill  United Kingdom
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There is absolutely no need to leave them on while you're not using them.
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Old 2nd April 2011, 09:42 PM   #7
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by bigwill View Post
There is absolutely no need to leave them on while you're not using them.
I agree, and further leaving filaments on with no cathode current flowing can lead to cathode poisoning which is a good way to ruin a tube.

IMHO It's a waste of power, a safety hazard and results in needless wear and tear on the power supply components and tubes.
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Old 2nd April 2011, 10:45 PM   #8
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Does your standby switch lead to the cathode exceeding heater-cathode voltage limit rating?

I anticipate a lot of the 'advantage' of leaving an amp on is the time to reach thermal equilibrium for all the parts in the amp. To that end, you could make a thermal cover and include a sort of 'anti-condensation heater' - a very safe type of heater, and tune it to keep the internals at about the same temp.

Burn-in, per se, is best done with power cycles, not just continuous operation - in your case this may be something like on for one day, off for one day - or strangely enough on during day/evening, and off overnight!

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Old 3rd April 2011, 03:04 AM   #9
ryuji is offline ryuji  United States
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I suppose, in theory it does in fact make it exceed the voltage rating only from the point of view that a resistance with no current means that there is no voltage drop across said resistance. heaters however are powered from completely independent power supply.
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Old 3rd April 2011, 03:21 AM   #10
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Most heaters circuits are referenced to 0V at some point - but maybe you operate just from an olde 'A' battery.

If a breakdown of the insulation in the indirectly heated cathode occurs then current would flow into a heater circuit that had some 0V reference, and you may end up damaging your heater/cathode.

One alternative typically done when a fuse is placed in the cathode leg of an output stage valve, is to keep a high resistance in circuit (which the standby switch shorts out) - such that voltage limit is not exceeded - sort of a very cold bias.

Ciao, Tim
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