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Dirty-South Blues Harp forum: wail on! >
How often should power tubes be changed?
How often should power tubes be changed?
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bharper
69 posts
Oct 10, 2011
5:59 PM
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I'm hoping to hear from the amp gurus about this. I use a 2 x 5881 amp, fixed bias set rather cold, with a 12AX7 phase inverter and a 5VR4 rectifier. In general, how often do you think the power tubes (and PI tube) should be changed?
The amp gets gigged a couple times a week, running close to its rated power since the stage volume of my band is rather high. I have not noticed any degradation in the amp's performance so far... The 5881 tubes are about a year old.
I'd rather not wait until the tubes fail or start to degrade. is there a rule of thumb on this?
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JBharmonica
65 posts
Oct 10, 2011
6:03 PM
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Preamp tubes (usually 12ax7's, small, in the front of the amp) handle less voltage and go through less abuse than the power tubes. They will last longer than power tubes. The only exception is the first preamp tube in a high gain amp - it gets hit pretty hard, so you want to make sure that a good quality preamp tube goes in there, and that it stays fresh.
Power tubes (the most common are 6L6's, EL34's, EL84's, and some others that are variations of these in name) are bigger, handle more voltage, are located at the back of the amp, get very warm, and tend to get abused a lot more than the preamps. They have a shorter life capacity in general.
Overall, the biggest factor in tube life is how much you use them and how gentle you are with how you use them. If you crank your tube amp every day for hours on end then your tubes will fail much faster than if you only played for an hour or two a week. Your tubes will also fail much quicker if you don't put them on "standby" mode (to warm them up) for at least a minute before and after you play them.
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JB
http://www.facebook.com/jbharmonica
jbustillos@gmail.com
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bharper
70 posts
Oct 10, 2011
6:10 PM
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Thanks. Do you wait for them to fail or do you replace your power tubes on some kind of calculated schedule?
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JBharmonica
66 posts
Oct 10, 2011
6:33 PM
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You can hear some of the harmonics of your tone start to dissipate...If you don't have a rigorous gig schedule then I would change them out about once a year...I have had bad luck with "bad power" situation...in this case a power conditioner is recommended.
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JB
http://www.facebook.com/jbharmonica
jbustillos@gmail.com
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5F6H
889 posts
Oct 11, 2011
3:47 AM
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You say the power tubes are fixed bias & rather cold? If around 15mA per tube or less, they should do 5 years of regular, hard gigging no problem...maybe more.
It's the heat generated that kills tubes, cold bias extends tube life. Even in a hot biased design you should expect 1000-2000 hours of gigging use (2 gigs a week, even with 3x 1hour sets is only 300hours).
Obviously if you do notice any degredation in tone then change them then.
It would make sense to change the PI at the same time but there is a lot of hogwash talked about PI tubes, they aren't biased any hotter than the other 12A#7 tubes in your amp, if the amp has a long tail PI then you normally, actively need to alter circuit values to unbalace it. If you want to buy "balanced PI" tubes, go ahead,but don't pay through the nose. Cathodyne PIs only use half a tube/one triode, so balance is largely irrelevant.
Even if you are running the amp at the highest volume you can get to before feedback, you are not stressing it anything like with hot bias & a strat (where the amp may mostly be working in the zone beyond it's clean power rating).
Never heard of a 5VR4, assume you mean 5AR4.
Many problems are caused at gigs by everyone plugging in to the same multiway AC connectors (causes a current bottleneck in the multiway, drags down heater voltage causing splatty tone) always try to plug your tube amp into the wall, use a long, heavy duty, single point extension if necessary.
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www.myspace.com/markburness
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bharper
71 posts
Oct 11, 2011
6:29 AM
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Mark, thanks for your reply; I was hoping you would weigh in.
Yes, the recto is 5AR4.
Since I hit the one-year mark on the tubes I was wondering if I should replace them. Thanks for your advice and expertise.
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