Gibson Tone Tips: Keep Your Tubes Happy
Back in the late 1960s certain factions in the amplifier industry went to great pains to introduce radical, new solid-state guitar amps and to promote them, partly at least, on the premise that they were “sturdier than fragile tube amps.” Tubes can be fragile if you don’t treat them right, certainly, but look after your tubes and the amp they are in and both should reward you with toneful and trouble-free service. In this installment of Tone Tips, lets look some easy ways to keep our tubes happy.
1) Let them warm up: Letting your tubes warm up for 60 seconds before switching the amp to “play” is not just an archaic function of an outdated technology, it’s crucial to preserving the life of your tubes. Tubes operate on two different types of electrical current, a low-voltage AC current that heats up their filaments, and a high-voltage DC current that drives their amplification duties. If the high-voltages DC hits them before the low-voltage AC has warmed them up it can do gradual harm to the components within the tube, and ultimately shorten their life. Most tube amps manufactured today have both Power and Standby switches. With the Standby in the off position, switch the Power to “on,” which will send the AC to the tubes’ “heaters” and start warming them up. After 60 seconds or so, flip the Standby to “on” to send the DC surging through the circuit and you’re ready to play—your tubes will be gently warmed up and ready to go. Some amps don’t have Standby switches, but more often than not they do carry tube rectifiers; because tube rectifiers themselves warm up slowly, they don’t send the DC voltages to the rest of the tubes immediately, but only gradually, once they have begun to warm up themselves. If you have an older amp with solid-state rectification (ie no rectifier tube) that is also lacking a Standby switch, I guess you either live with it that way, or pay a qualified amp repairman to install a Standby switch (although you will want to avoid devaluing any vintage amplifier, or voiding the warranty of a new one).
2) Let them cool down: When you’re done playing, switch the Standby off first, then the Power after a few seconds. Now, even though the amp is off, let it cool down for several minutes before moving it, or certainly before handling the tubes. Vacuum tubes are most susceptible to damage when hot—which renders their internal components more fragile and pliable—and moving the amp or handling the tubes before they have cooled down can lead to premature failure. There’s another reason to let tubes cool down if you’re swapping them, for tone-tasting or general maintenance: these things get hot! A fully-heated power or rectifier tube in particular can inflict a nasty burn. Let them cool down, and preserve both your tubes and your fingers.
3) Avoid excessive physical shocks: Even when cool, tubes can be damaged by excessive jolts or vibrations. On the whole they are usually a lot sturdier than those solid-state amp manufacturers might suggest, but hey, good tubes are expensive, and you might as well get as much life out of them as you can. Obviously you want to avoid dropping, knocking over, or heavily bumping your amp, but you should also avoid the kind of jolts and major vibrations an amp is subjected to when you put casters on it and roll it down a bumpy driveway or sidewalk. Rolling a road case with casters is usually okay, because these things have heavy internal padding, but I have known more than one guy who rolled his Twin or AC30 from the parking lot to the gig, and was dismayed when the thing failed to function on power-up. Roll it across the smooth tiled or wooden or carpeted floor, sure, but carry it over bumpy ground, please.
4) Use (or install) tube clamps: While many tubes will hold themselves in their sockets perfectly well, tube clamps—which come in various formats—will both help to prevent tubes from plummeting to their death if your amp should be bumped or dropped, and will also help to maintain a tight electric contact in the tube socket. The latter point is one that is too often overlooked; even a tube that seems to be seated tightly in a tube socket in a non-moving amp might jiggle, vibrate, or shift around in its contacts during the vibration produced simply by playing at high volumes, and in doing so might cause crackles, noise, or intermittent faults. Tube clamps are most often seen as simple “claw” types (a bent metal retainer with teeth that grip the base of a 6L6GC, 6V6GT or EL34, for example), or as a pair of springs and retainer cap, sized for use with 8-pin tubes or 9-pin output tubes such as EL84s. Another popular retainer for the EL84 is the simple bent-wire type of clip, which also works perfectly well. If your amp has no such clips you might consider having a qualified repairman install a set. Most preamp tubes have metal shields with internal springs that help keep them in place, although these tubes are smaller and lighter than most output tubes anyway, and therefore are less in danger of falling from the amp.
5) Keep your tubes cool: As distinct from No. 2 above, “Let them cool down,” tubes are also happiest when kept as cool as possible while operating. This means ensuring there is adequate air flow through the amp’s cooling vents, and never playing the amp in an enclosed box, small closet, or with its back up against a wall or a road case that might impede such air flow. Beyond this, installing a purpose-made fan to cool the output tubes in a large tube amp (which can usually be switched off for recording), or even using a small, quiet fan behind the amp, can really go a long way toward extending tube life.
6) Use the correct speaker impedance: Mismatching your amp’s output and your speaker(s) total impedance load will strain both your output tubes and your output transformer (OT), and possibly lead to premature failure in either or both. Most tube amp’s OTs will tolerate an impedance mismatch of 100 percent in either direction fairly well—that is, connecting a cab of either 4 ohms or 16 ohms to an amp with an 8 ohm output—although doing so will strain the tubes more than a correct load, and might also impede your amp’s full tonal performance.
7) Bias your output tubes: Some tube amps such as cathode-baised types or those with preset fixed bias circuits don’t require biasing. Just pop in the correct type and grade of replacement tubes and off you go. If your amp is one that is meant to be biased when the tubes are changed—or even as an element of routine maintenance when the output tubes are being retained—then do so. Tubes running at the wrong bias setting will not only age prematurely in many cases, they simply won’t sound their best, and that’s what it’s all about. There are a number of kits available today to let players safely bias tubes themselves, or any qualified amp repairman can perform the function for you for a nominal fee.
Buy good tubes, keep them happy, and maximize your tone. You know it makes sense.
[originally by Dave Hunter | 01.10.2008, Gibson.com]