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Does tube failure occur most often during turning on the amp or is this something that occurs at anytime? I have had my tube amps (MC40s) for about 18 months and have not had a problem, just something I was wondering about. The amps have were freshened up a few years ago.The reason I asked, is that I have heard said that a person should not leave the listening room for an extended period of time, in case of a malfunction and possible fire hazard. Is this a legitimate concern?
Thank you for your input.
Follow Ups:
I've been using tube amps for about 3 years and have only had one failure. A power tube failed in my Cary SLI80 and it was quite dramatic (i.e. the noise through the speakers). The tube had been popping for a few days beforehand and I should known it was coming. I used to fire the amp up and let it warm while I went to the store, etc., but the failure has broken me from that routine. However, given the generally excellent reliability I have otherwise experienced I don't worry about leaving the amp on if I'm in or around the house. As several have mentioned, turning it off and on is worse on the amp than leaving it on (I believe the Cary website may talk about this in the FAQ's). Turning an amp off to take out the trash and such is a little cautious IMHO. But to each his own.
On the weekends sometimes I turn on my system in the morning and leave it on all day. Hours on end unattended.Preamp
Sonic Frontiers Line OnePower amp
Audio Research VT5099% of the time the top covers of the equipment are installed.
I grew up on tubes as a kid and teenager. In the 90s I went back to tubes. I have never had an experience as some have described here. I guess I am just lucky.....
Hello Steve,
I always watch the amps when I fire them up. Many times you can spot a arcing output tube or rectifier on startup ( I realize the MC-40s have SS rectification). The failure mode that is most dangerous however is when a tube "runs away" and starts conducting *WAY* more current than it is supposed to. If a tube runs away unchecked it is very possible to blow an output transformer before the fuse pops from the over current condition.I had a JJ E34L go nutz on me about a month ago in one of my living room system's Dynaco Mk IVs. We were having dinner and the amps had been powered up all day (like 7 hrs). The system was not playing music but I heard the tinkling of a hot tube's glass. I walked over and found the problem just as the fuse blew. It took out a grid stopper resistor and did no other damage other than the tube is toast.
I have been running those amps 12+ hrs a day lately (not working as much as I would like to), so I was glad to be nearby when it happened.
I lost a power transformer on one of my Heathkit W5-Ms that way a decade or so ago also. That was a very acrid, smoky event. The potting tar was running out from underneath the amp like it was water! Hello Fire dept? I was glad they were on the concrete floor!
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Al G
I appreciate your input. I did have a tube go bad on my Sansui 1000A about 6 months ago upon firing it up. I always watch everything come up when I turn the system on, and I saw a real bright light come from under the cover and immediately turned it off. I took it back to the guy I had bought it from and he checked it all out and called me the next day that it was ready to sing again.Is Meechigan starting to warm up? The songbirds returned here about 2 weeks ago and the trees are about to burst. I am thinking about killing off my lawn. Mowing isn't all it's cracked up to be.
It has been sunny for TWO DAYS straight! Almost 50 deg f today. Still a foot of snow in the yard tho...The blue jays are back as well as the cardinals. Still no finches.
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Al G
66 degrees in Potomac, MD
Ha, 72 F here in south spain.
It seems like I am doing it the correct and safest way, only having my amps on while I am listening to them. I will leave the room, but only for less than 5 minutes and then return to listen. I appreciate your feedback. Thanks
I have had one tube failure and it was a "run away" situation which occured at start up. Luckily, my amps are pretty hearty and I cut it off before any damage was done to my amp.In regards to leaving the amps on and leaving the room. Here is my approach. I am not going to leave the house with them on, but if I am going to be out of the room for a few minutes, 15 or so - I don't turn them off. (It's more stressfull to turn the amps on and off then just leaving it on)
But I would not leave them unattended for an extended period of time.
turn on the stove/oven and go on vacation? How about the clothes dryer? Maybe a light bulb?It depends on your comfort level. Some wouldn't leave the house with a tube amp on. Some leave it on 24/7. Me?...I wouldn't leave it on unattended for more than a few minutes. It is too easy for something weird to happen.....you know the cat decides to piss on it and his fur cathes on fire....lol.
I will leave a light on when I leave but if I'm gone for more than a few minutes e.g. taking out the trash, I shut the amp off. Ask my wife about my obsessiveness about the washer and dryer:)That said I've never had anything untoward happen with an amp of either type, SS or tubes.
Heaters rarely fail. By far (95-98 %?) tubes just wear out, meaning that cathode emission falls to a level where you hear a difference. Other structural failures within tubes can cause shorts, which are invariably catastrophic for the tube and sometimes for the amp.In terms of safety, tubes are pretty darn reliable. I would guess that they are no more of a fire hazard than transistors are.
Yup, that has been my experience, tubes just slowly die. So, is it better to turn off amps for relatively short interruptions in listening or is it better to leave them on? Is there any issue with cathode stripping from turning on an amp and is that less of an issue with tube rectification?
the most stressful time for a tube is at the moment it is turned on. The filament that heats the tube is cold. Because it is cold it conducts current with very little resistance as compared to when it is at operating temperature. That results in a huge surge of current that very rapidly heats the filament. The thermal shock (rapid expansion from heating) resulting from the rapid heating stresses the filament. It is the same reason why light bulbs rarely fail while in operation, and almost always "blow" at the moment they are turned on.Tube gear that utilizes a tube rectifier (device that turns AC into DC) are kinder on the rest of the tubes. The rectifier itself needs to be heated before it starts to conduct. So, the rectifier delivers juice more slowly at startup than solid state rectification. Most rectifiers are themselves fairly rugged and can withstand the initial turnon surge, though I am sure they would benefit from a slow start circuit too.
Some tube gear employ slow start circuits that gradually increase the juice to make the startup thermal shock more gentle. A device called a thermistor is often employed. It has the property of having a higher resistance when it is cold than when it is hot; as it heats up it slowly allows more and more current to flow.
... and maybe, just maybe, because I'm a little lazy. And embarrassingly, I've been known to return from a trip to, say, Radio Shack and finding all those lights atwinkle. This is dumb.But geez, I've got two SET monoblocks, a tubed linestage, a tubed phonostage (with a tubed power supply), and a tubed tuner. If I routinely turn everything off when I leave the room, it takes time (at least 20 minutes) before the system starts sounding "human" again after turning it back on. And the extra turn-on stress is something to keep in mind.
So I've been lucky (knock wood), with tube failures -- the dramatic kind -- happening only at turn-on. No excuses, just my particular accommodation to the situation.
Interesting subject. I am running Audio Note Conquests 300b's with TJ Solid Mesh Golds.I switch on each day of listening, go out on short trips leaving them on, otherwise switch of.
I do this partly as the electricity supply in Spain can just go of, and back on with no prior warning, partly the amount of new construction going on and muppits dig out the cables in the road etc.My amps seem to have a thermistor, as the sound from the 300b's is delayed by 30 seconds, when you start to here the background hiss coming on.
I have had hassles in the past with cheapo standard issue Sovtec rectifier tubes and Golden Dragon 300b's just going and shorting out.
My view, go for sonics, but also check out the reliability of the valves. Many are not too good, particualrly the cheaper alternatives. It just don't make sense buying budget tubes if there could be possible damage downstream.
Other thing I guess, is have the amps checked every couple of years, and visually check the insides yearly at least, aspecially if you have a tube go. Cap leaks and transformer oil leaks can be easy to spot. And if you live in a damp invironment, look out for green corrosion marks, particularly if stores away for a while.
And all NOS valves should be carefully examined before use, cleaning the pins with alcohol and silver polish. look through a magnifier for loose connections etc. I had a calapsed D getter on a Tungsol the other week, nearly popped it in!
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