When to replace tubes?

Sorry if this seems like too basic a question, but when should one replace the tubes in ones amp? I bought a Jolida amp about 6 years ago and I'm guessing I use it on average an hour a day. So I figure it's been used about 2000 hours so far. If the sound has worsened I can't tell because it will have happened very gradually.
I do know that the bias LEDs don't always come on now. Thanks.

 

Tubes last a very long time. I have radios and amps from back to the 30's which still have some of their original tubes. Tubes can be tested to check their conditions. With the expense these days of quality tubes, I test them before considering replacement. What does go bad are the electrolytics and capacitors, plus sometimes resistors. I've seen some high-dollar newer amps which were built using cheap-o caps made in China. Sometimes you have to learn through trial and error, but it is inexcusable to build amps costing thousands of dollars and use cheap-o components. What is under the chassis that you don't see determines the life of tubes.

 

I have a hybrid headphone amp. When I notice hiss or noise when plugging in a sensitive (efficient) headphone it is time to plan on replacing the tubes. I may not notice the hiss with my regular headphones, but I'll be able to hear it with the more sensitive and efficient headphones. The tubes haven't failed yet, but have degraded to the point that they've become noisy.

 

Actually, it is a good question. In my opinion, you replace one tube when it fails. When more than one tube has failed, it is about time to replace all of them. Your bias LED is just to check bias, not to evaluate the condition of a tube. And bias is a lot less critical than people make it out to be. Even matching is over-rated, although I do my own approximate matching with a mutual-transconductance tester.

It would be best to find some spare tubes, same as the tubes you are now using, and have someone grade them, to approximately find matched sets. Then you only have to replace one tube at a time, until you run-out and have to start all over.

 

You will know when your tubes go bad. If the sound hasn't worsened to your ears, then you are OK. I think tubes often last a lot longer than many experts claim. For example, Robert Harley claims that tubes in pre-amps need changing after 1,000 hours!! Most others will say you should get 5 to 10,000 hours out of them. I've had the same tubes in my preamp for four years now and it still sounds great. My headphone amp, although I don't use it as frequently, is still going strong on the same cheap stock Russian tubes for a good five years. Just have some spares ready and when you need to replace your tubes, you'll be good to go.

 

If you have a 302B -- Jolida gives the life expectancy of the tubes 6 years. Without having access to a tube tester, it's anyone's guess. The Integrated amp does not have a slow tube turn on feature which I suspect coupled with the daily use over 6 years could warrant an owner to search for replacement output tubes only. The 12v tubes are likely to have quite a bit more life in them; more so than the EL34's IMO &I'd leave them alone.

If the bias LED's no longer illuminate or are intermittent, I'd say it's time to replace the EL34's. For instance, Svetlana matched quartet of EL34 tubes can be obtained for around $100.

Best Sir,

Bob

 

I don't understand what 6 years life expectancy means. Is it an hour a day x 365 x 6 years (4500hrs)? Or is it 5 hours per day x 365 x 6 years (20000 hours)? It's silly.

 

It is often difficult to assess, by ear, how much a tube has degraded from age. Your best "solution" is to buy a complete set of replacement tubes, and once in a while, put that set in to see how the sound has changed. If you still like what you hear, it is not time to do a replacement. A second set is really more useful than a tube tester. Some tubes will test good when they really don't sound good any more, and some testers will show that a tube is weak (which may be true electrically speaking) that still has some decent sound left in the tube. If an amp runs tubes gently, even weak testing tubes can sound good.

 

My late 50s and early 60s tube amps are still using most of their original tubes. As long as the rest of the amp is still running within specs, you shouldn't need to worry about changing tubes unless you audibly start to hear one fail.

 

Yes. Setting a particular life expectancy is silly, without giving the conditions. Amp in use 24/7 for 6 years or intermittent use. As with light bulbs and other electrical devices, the greatest amount of wear occurs each time the unit is switched on. Intermittent use may shorten the life.

 

What will you hear if one is failing?

 

Fair amount of play, bias level off...at the very least you should always have a set of tube spares around for when and if, but really when, a tube fails, anyway, so I say time to by a new set of power output tube and at least swap 'em and see how they sound. Then you can keep the new or old tubes around as spares.

In my experience, with power output tubes, some of them -- older production ones, not so much new production ones -- will "last" a long time, but when you swap in fresh ones its often surprising how much quieter, more dynamic and crisper at the frequency extremes things seem to be with the fresh tubes, even though the old tube are working "fine."

 

If there is a change in the sound, then it's worth checking out the amp regardless of what you think the problem is. First thing is to check the tubes, having them tested if possible. If the tubes are good, then start looking at capacitors. Even if the tubes need changing, it doesn't hurt to have someone check the capacitors too, since they could be responsible for the tubes biting the dust.

 

Average life for power tubes is 1500 to 2000 hours.

 

That was about what I was going to say, about 2,000 hours. That is an estimate for the large power tubes like your EL34's.

Because of the number of hours on your current set of tubes, when one of them goes bad, I would replace the whole quad, with a new matching quad.

That way, your system will be at it's best possible performance.

Keep the old set and use them as replacement's, when your new set gets high hours and they begin to fail.

Do this as each of the new tubes begins to fail, until, you have used all three of the old tubes.

Then buy a new third set and replace the the whole second quad with the third set and retain the three still functioning tubes from the second set, to use as back up's for the third set.

Repeat...

Your small signal tubes should last three to five times longer than your larger power tubes.

 

that has been my experience about 5 years based on 365 hours a year>=1825 hours. I tend to replace ALL the input tubes at the same time due to their low cost even though they last longer.

sean

 

I don't think that the idea of an average life for power tubes is at all useful. So much depends on the type of tube, the particular design of the amp the tube is being used in (some amps drive tubes much harder), the way the owner uses the amp and the particular manufacturer and vintage of the tube. For example, I know of a particular 300B amp that owners have not had to replace the Western Electric-sourced power tubes after more than 15 years of fairly heavy use; others running the same model of amp with different brands of tubes have had to do more frequent replacement; and with one particular brand, the tube would start to flash and make sputtering sounds after 15 minutes of operation.

I run 348 and 349 tubes in my amp. I have not had to replace any tubes in the six years or so that I have owned the amp and the builder says that the tubes will last for many more years (the tubes were used, old stock when I bought the amp). This is a good thing because the amp runs four of each of these tube types and replacement tubes now cost north of $1,000 each.

 

Just in the past few days I have heard inadvertent "crackling" from time to time when music is not playing.
Is this probably a tube issue?
They are 3 years old.

 

Tubes can last a long time, or not depending on how they are used. They can be more rugged than you may think. Like light bulbs any can be subject how often you turn them on & off. The design of the tube can also be a factor. If the original design was for mission critical purposes, like military, then they can last a really long time, which is why some vintage tubes have the JAN designation (Joint Army / Navy). Vibration can shorten a tubes life too. However, if they still sound good to you don't stress it. On the other hand if you start hearing loud popping from one or both channels, they have begun to arc, power down immediately so you do not damage your equipment.

 

Probably, just had the same symptom on a pair of 6L6 guitar amp power tubes, occasional pops with no signal, and getting crackly when turned way up. You only equipment with preamp tubes listed though.

 

This is from guitar amp knowledge....
When noise or bad sound occurs, but 1st check preamp tubes and look for an individual bad tube and replace just the one, then listen again..It'll usually be V1... If you have zero tech ability just wait for bad sound. That said, if a tube doesn't light up replace it. Swapping preamp tubes in and out and listening is something anybody pretty much can do. It is the 1st step unless there's something obvious like a power tube not lighting up or red plating... (the tube will be much brighter lit than usual and plate will be red hot and disaster is eminent)also called thermal runaway or other nicknames.......sound will be horrible...

I would advise buying preamp tubes from a supplier who grades specifically for noise and pay extra for them... Dougs tubes sell some ruby tubes that way that I have used for noisy guitar amps.

Power tubes
Power tubes generally should be replaced in sets, being match is important. A tube is degenerative and wears over time, in push pull it's a good idea to periodically check bias and adjust as needed. If bias current match is over 5ma apart and has a noticeable effect on sound, replace the tubes. If more than a 5ma difference, probably replace the tubes. If it 6 or 7 ma apart but you think it sounds great, roll with it for a little bit, but know replacing tubes is in relative near future. For cathode bias without a tube tester, just wait for bad sound, assuming you know your preamp tubes are good. (In hi fi it's possible that a 5ma difference may sound bad, but not usually the case with guitar amps, it can add character..maybe totally undesirable in hi fi--use your ears)



Orange makes a simple user friend tube tester that could be used to test match and see if tubes are in spec....One could just pull the tubes out and test them periodically...
Wish it was cheaper, which is why I haven't pulled the trigger.
Valve Tester – Orange Amps

 

It's time.