How to get the best performance out of your guitar tube amp and keep it pumping out great sound
Nothing beats a tube amp when it comes to generating fat and crunchy tone. From subtle compression and sustain to all-out grind, valve-based circuits have been the holy grail for rock and blues guitarists since the earliest days of the electric guitar.
But those circuits are based on technology that goes back to the mid 20th century, and unlike their solid-state counterparts, they can be a little temperamental. Having a little knowledge and taking a few precautions will keep your amp hitting on all eight cylinders with minimal maintenance and fuss.
Treat her right
Most tube amps have a standby switch that keeps a low-voltage current flowing through the tubes when you’re not actively playing. This preheats sensitive tube components so that when you start cranking the volume, the tubes already are up to operating temperature, thus extending their life. If you’ve ever moved a chilled glass container to a hot oven or microwave only to watch it develop sudden cracks, you get the idea. Make it a practice to put your amp in standby mode for a few minutes before cranking up the juice.
The filaments and plates in power and preamp tubes are delicate and won’t tolerate a lot jostling. Sockets can loosen during rough handling resulting in erratic performance. Handle your amp like you would a fine old instrument—gently. Loading in and out of a gig can be an especially dangerous time for your amp—particularly if you depend on a roadie or volunteer feeling his testosterone.
If it ain’t broke…
Although gentle handling should help prolong tube life, like life itself, there are no guarantees. Relatively new tubes can suddenly and inexplicably fail while older ones may keep going for decades. That’s especially true for preamp tubes.
The old adage, “If it ain’t broke don’t fix it” holds especially true for guitar amp tubes. On the other hand, failing tubes can sneak up on you. If you sense that your amp isn’t generating the presence it once did, aging tubes are the likely explanation. The same goes for an overall drop off in volume. If you find yourself cranking your gain or volume knob to higher settings than usual, tubes that are on the way out could be the culprit.
If you use your amp often and play at high volumes, you may need to change out tubes annually. Occasional players will need to swap tubes less frequently. It’s sort of like the frequency with which you do oil changes—the more you drive the shorter the intervals between maintenance.
Random electronic buzzing and pops can point to a failing tube. Aging tubes can also produce microphonic squeals and howling that don’t necessarily go away when you turn down, signaling that a new set of power tubes is overdue.
Choose the right tubes
Generally you’ll want to stick with the tubes recommended by the amp manufacturer. That said, some amp manufacturers such as Randall include biasing controls that allow users to switch out tube types. But if your amp lacks such functions and you’re intent on swapping out say 6L6s for EL34s, we recommend you see an experienced amp tech.
Short of using sophisticated test gear, a visual inspection of your powered-up tubes can help you determine if your amp’s biasing is in the ballpark. Tubes with a soft amber to orange glow are probably getting the right amount of current. On the other hand, if they emit a purple to blue glow, they’re likely not getting enough juice.
Some tube manufacturers such as Groove Tubes and Ruby offer matched tube sets that have been tested for similar electronic characteristics. Since power and preamp stages equipped with mismatched tubes can compromise your amp’s sound, a matched set is likely to be a worthy investment.
In Part 2 we’ll address troubleshooting your amp and take a look at preamp tubes in depth. Stay tuned and keep on rockin’.
Shop the big selection of guitar amp tubes at Musician’s Friend.
Learn more with our Instrument Amplifier Buying Guide.