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When to change tubes?

Discussion in 'Amps and Cabs [BG]' started by ballmasterflex, Apr 9, 2004.

  1. I really like the tube sound but I am hesitant to buy an all-tube amp because of maintenance costs. When, on average, do you need to change tubes if you play a few gigs a month and practice 3 times/week? Are there other maintenance costs that must happen regularly? What is adjusting the bias?

  2. Contrary to some opinions, tube amps (if treated with a reasonable amount of respect) don't need a whole lot of maintenance. Tubes can last for years or even decades. I've got a 30+ year old Ampeg that had seen regular use, yet all the original tubes were still good.

    Biasing is an adjustment that regulates the amount of current the power tubes draw at idle (preamp tubes don't need biasing). Some people think biasing must be done every time you change your tubes. At the other end of the spectrum is the opinion that biasing (once done correctly) isn't really necessary unless changing to a drastically different tube. I tend to gravitate towards the latter theory. I loaded up my old Ampeg with a slew of different brands of power tubes (without messing with the bias), even tried a mismatch of four different tube brands, and measured the exact same output power regardless. And to my tin ears I couldn't hear a noticeable difference in tone between them.
  3. The new GE 6550A's that I put in my vintage svt should last me a very long time. That being said I usually could only get 2 to 3 years out of a set of Sovtek 6550WE's. You should always bias an amp when you put new power tubes in it, and its pretty easy to do on an svt. The power tube bias will also drift a little bit over time (and also as new tube are broken in). A tube amp will start to sound dull and kind of mushy when the power tubes get old and my also lack volume as well.
  4. MrBonex


    Jan 2, 2004
    New Hampshire
    Even if you don't change tubes for 3 or 4 years, the sticker shock of buying 6 KT88s is substantial (what I've got to do with my Trace Elliot V6). So, all I can say is "be prepared."

    That said, I'm a tube guy. I think it's worth it.
  5. Thornton Davis

    Thornton Davis

    Dec 11, 1999
    I'm on my 6th year without any problems with my 8 Sovtek 6550WE tubes.
    If you take a bit of care and let your tubes warm up for 2-5 minutes before you play and then give them 5 minutes to cool down when you're finished, they will last for years.
    You should bias the amp when you install new tubes, if for no other reason to be on the safe side in my opinion.
  6. Bridge Cables

    Bridge Cables Gold Supporting Member

    Mar 23, 2003
    Southern N C
    Your power tubes should pretty well last for decades. Unless they manufactured improperly, biased wrong or your doing some major amp tossing.

    Here's a very good cover of the topic by Psycho Bass Guy, check p2 about halfway down the thread.


    PBG has answered alot about the "non-biased" Mesa's for me. Think I need a mod on my old D-180, just to tweak the bias. Hmmm, TN ain't that far from NC!

    BC :cool:
  7. i hope the tubes in my trrace last me longer - i bought the thing used some months ago.

    Thornton davis, youve got pm!
  8. thanks a lot peoples...
  9. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    There are many reasons why it's good to have your tube amp checked out by a qualified tech every couple of years. Especially high power bass amps like SVT's. One of the main reasons is that components drift out of tolerance over time, and some of the component values are critical to the proper functioning of the amp. Another reason is the electrolytic capacitors, which have a useful lifespan of maybe ten or fifteen years (regardless of how often the amp gets played). Another reason is that the tubes wear out over time, which changes the electronic conditions in the amp. One bad component can cause others to fail. And so on.

    A tube amp is like a car, it requires periodic preventive maintenance to keep it running in good working order. The "if it ain't broke don't fix it" philosophy definitely doesn't apply to tube amps (well, it might, but the risk associated with that approach is enormous, if your amp's still working after twenty years under those conditions consider yourself lucky). That's one of the big advantages of point-to-point wired tube amps in the first place, is that they're easy to service. It's well worth finding a good tech and paying him a hundred bucks a year (or whatever) to make sure your amp keeps running smoothly.

    Bias is one of the things that should be checked periodically, in relation to the tubes growing old and wearing out over time. "Biasing" your amp is like setting the idle in a car, and just as you'd tune up your car periodically, it's a good idea to tune up your amp once in a while. As the spark plugs wear (or the tubes wear), conditions will change inside the system, and a little tweak every now and then can be helpful.

    IMO there's no such thing as a maintenance free amp. That would be an unrealistic expectation. Mostly it's a question of user serviceability, and that's another area where tube amps excel. If you keep good tubes in them, most of the other components will last a good long time (thirty or forty years or more, as you say, except for the electrolytic caps, and even there you might get lucky).
  10. vacman


    Mar 8, 2004
    portland, or
    Amen Brother!!!! You Know your stuff....I have had an SVT for eight years and retubed it twice. Yea it costs abit but man is it worth it IMHO. Solid State for me just doesnot have the same WARMTH.
  11. I take issue with some of this. While it's mostly true in spirit, there are some details that aren't correct.

    This is 100% totally dead on. Especially in amps like an SVT, drift in components like plate and grid resistors have a definite direct impact on amplifier performance.

    That's not right. Capacitors wear out as their electrolyte dries and loses its ability to store energy. They wear out more with disuse. Literally, a piece of equipment that sees more regular use will have "healthier" capacitors than one that sits idle. Humidity also has a LARGE and definite impact on capacitor lifespan. Dry climates age them much more quickly than wet ones.

    This, while true to an extent, is misleading. Yes, tubes DO wear out, but the cathode is the element that wears out. That means the tube emits less, but its voltage handling and current capacity are not affected by cathode wear. Those exhibit the greatest changes early in tube life and are generally stable once a tube had been "burned in." It is voltage handling and current capacity of a tube that affect the other components the most.

    This is 100% correct as well, but the biggest culprit of component drift is heat, NOT tube wear, which has a cumulative effect on parts like resistors and capacitors. The heating and cooling process can crack resistors and change their impedance which changes the overall circuit.

    ANY amp requires periodic maintenence. It's the kind that makes the biggest difference. If people swapped out output transistors like they sometimes do with output tubes, solid state amps would also require the exact same attention.

    Yes it certainly does. The rub comes from how you define "broke." An amp that needs bias adjustment or component replacement is not in proper working order and repairs and adjustments made to it are NOT "routine." They're repairs.

    This is alarmist and misleading. If an amp works, then unless you notice a change in its performance, chances are that it IS just fine.

    You've obviously never had to fix a small Silvertone. PCB's aren't evil, nor is an amp necessarily better because it is "point-to-point" wired. The SVT is a combination of point-to-point and boards and the board mounted components are no more hard to service than the p-t-p parts.

    No arguement here, but it's the same logic behind knowing a good mechanic. A tech fixes what's malfunctioning; he doesn't change the oil or pump gas.

    Tube bias current draw isn't a function of tube wear as much as it is construction. This is a decent analogy on a superficial level, but it's also misleading because...

    Tubes are more like gasoline octane than spark plugs. They're the amplication factor. Spark plugs are more analogous to regulatory circuitry, and cars and amps don't operate the same way, nor do they do the same thing.

    If a tube amp is running right, there is no "tweaking" to do.

    I agree, but you're exaggerating the need.
  12. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Okay, fair enough. That's certainly a valid viewpoint. I can tell you how I approach my own amps, which is that I'll try to replace tubes "on schedule" whenever possible, instead of waiting till one of them goes bad. This would be especially true of current production tubes, many of whichi only last a few years. Some are better than others. Some of the older tubes last longer than the new ones (like the Mullard GZ34 is legendary for its longevity). And in all fairness, some of the newer current production tubes haven't been around long enough to be able to make that judgement. Let's just say it's been a pattern up to this point in time, at least that's been my experience. While it's relatively rare for a tube to actually short out (most of the time they just die), some of the Chinese tubes are notorious for arcing and shorting out, and those I wouldn't run in my amp "at all", or if I had to use 'em for an emergency at a gig I'd get them out of my amp as quickly as possible. But my rule of thumb for amps that are used "regularly" (I think that would apply under the conditions mentioned) would be two years for current production tubes, and five years for NOS tubes. That's just a general guideline, everyone has their own numbers. All I'm saying is that it's a good idea to catch the bad tubes before they crap out, 'cause if one of 'em does short out it can cause other (expensive) damage to the amp.

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