Tu-be or not Tu-be
Questions and Answers on New Old Stock Tubes
Part 5 - Care and Maintenance of N.O.S. Tubes
How long do audio tubes typically last?
For small signal tubes, my experience is that they last between five and ten thousand hours. Power amplifier tube life depends in large part on the particular amplifier used- some are much harder on tubes than others.
How can one tell when a tube is reaching the end of its useful life? Are there any telltale signs?
Yes. A tube will start sounding a little soft on top and rubbery on the bottom when it's getting ready to go. The tube will start sounding veiled and lifeless and the dynamics will sound restricted.
A lot of people envision tube failure as an "explosive" event- is there much truth to this notion?
Most tubes just sort of peter out. Occasionally, you'll get a power tube shorting out, but that's a rare event. Small signal tubes tend to die a "natural death".
So it should be no secret to the tube owner as to when his tubes reach the end of their useful life
Well, its sort of like gaining five to ten pounds per year- you don't realize when its happening then suddenly you realize "wait a minute-what's going on here".
[At this point, your interviewer pauses to glance at his waistline, ruefully observing the after-effects of five years at a desk job. The interview continues ]
What can be done to preserve tube life?
Well, if you leave your preamp on all the time, you can count on re-tubing every 12 to 18 months, typically. If you turn it on and off, I think you'll enjoy much longer tube life. There are a lot of opinions on that subject and quite a bit of controversy as well. I'd say if you know you're not going to be using your equipment for a few days, turn it off. However, a number of manufacturers incorporate "constant on" filaments into their products, making this less of an issue.
Another tip I can pass on is that if you buy N.O.S. tubes, sometimes they'll have a light layer of dust on them from sitting around for so many years. You might want to carefully clean them off using a cotton swab and a little rubbing alcohol to make sure that the glass is very, very clean, which will allow the tube to dissipate heat easier and quicker. Be careful with the logos when you're doing this, however, as they're made to be easily removed.
I also recommend that you get an emory board and clean the pins at the bottom of the tube. This will make a big difference- you've got to keep those pins clean. Dirty pins can make even the best tubes sound noisy.
[Ed. Note: The practice of using an emory board on tube pins is itself a somewhat controversial practice. The abrasiveness of an emory board may result in rough surfaces on the tube pins. Rough surfaces are definitely NOT as good as mirror smooth surfaces for good connections and conductivity. A rough surface, by definition, will not provide the same degree of surface-to-surface contact as a smooth surface. The better practice for cleaning grungy tube pins may be to use a silver or brass polish to clean the pins, making sure to remove any residue before re-inserting in the amplifier. Also, don't over-clean dirty gold pins- an occasional light cleaning will be more than sufficient.]
Finally, and I cannot stress this enough, DO NOT TAP ON HOT TUBES! I can't tell you how many people call me up and say "Kevin, those tubes you sold to me make noise when I tap on them". Well, of course they make noise when abused in this manner. You can actually damage the tube by tapping on it when it's hot, so don't do it.
Should you use emory boards on tubes with gold pins as well?
No. If gold pins get grungy, you can clean them with Tarn X.
Is there any way to recharge a worn-out tube?
No, or at least none that I've ever seen. Tubes wear out then the cathode can no longer supply electrons. The only thing I've ever heard about is turning up the filament voltage for "x" period of time, reducing it to normal, then praying. I've tried it, but thus far, my prayers have not been answered
Have you had much experience with products on the market designed to improve tube performance, speaking from a N.O.S. point of view, such as Top Hats, tube socks, etc
Top Hats absolutely do work. I've run tests on them and they do reduce microphonics and the tube's sensitivity to vibration. They're reusable and I've never run across any ill effects. I've had a couple people say they've reduced the sense of air that they seemed to have before, but
I'm wondering if the people claiming a reduction in the "sense of air" are simply confusing "air" with actual microphonics
That's right. A slight amount of microphonics is what many people perceive as giving tubes "life".
Are there any other items of ancillary equipment that the tube enthusiast should have handy?
I think it's good to have a mutual conductance tube tester handy. The military TV7 is a nice unit- it's compact and built like a tank. Any of the Hickoks would also be good. The B&K 700, 707, and 747 are popular and easier to use than the Hickoks.
Are any of these units still in production?
No, you have to hunt them down on the used market, which is always a thrill because you don't know if they're working properly or not.
What range of prices are, say, the Hickok units going for on the used market?
Anywhere from $50.00 to $300.00 or more depending on the model and condition. Here's another hint- if you see one for sale, ask if it works. If the answer is "I don't know ", please allow me to translate: it doesn't.
...continued in Part 6 - Final Thoughts