Tips to Extend the Life of Vacuum Tube Guitar Amplifiers
- Feb 16, 2011
- in Guitar Kit Builder - Amplifiers
Here are some time-tested tips on how to avoid causing damage to, and for extending the life of, your vacuum tube guitar amplifier:
1. There are dangerous high-voltages inside the amplifier that can cause shock, injury or death. Due to capacitors which store an electrical charge, these voltages can be present even when the amplifier is turned-off and unplugged from an electrical outlet. Unless you are a qualified electronics technician, do not take your amplifier apart or remove the amplifier chassis from the cabinet.
MOVING & TRANSPORTING
2. Avoid physical shocks to the amplifier cabinet, such as dropping, bouncing or vibration. Use padding around the amplifier when transporting in a car or van to avoid having your tubes or other components shaken loose, which could lead to microphonic rattles or other problems.
3. After using your amplifier and shutting it off, let your amplifier cool down for a few minutes before moving it. Many of the amplifier components are more vulnerable to physical shock damage at operating temperatures.
CHECKS BEFORE POWER UP
4. Check the AC power cord to ensure that it shows no signs of damage or fraying. If it is damaged have a competent technician replace it with a new cord.
5. Check that the electrical outlet used is properly grounded. This is for both safety and hum-reduction reasons. For a few dollars you can purchase an electrical outlet ground tester that will indicate if the outlet is properly wired and grounded. See a local hardware store, Home Depot, Lowes, or Amazon.com to purchase one of these testers.
6. Check that the speaker(s) is properly connected before turning on the amplifier. For combo-type amps with a built-in speaker this would typically be necessary after transporting the amplifier, when speaker wires could have rattled loose or been snagged by other equipment through an open-back cabinet. For amplifier heads check that the speaker cable is properly plugged-in to the amplifier and speaker cabinet. This cable typically uses 1/4" jacks of the same type used to connect the guitar to the amplifier, however do not use a guitar cable for this connection. Use only speaker cables made specifically for the amplifier to speaker cabinet connection. These cables are made for the higher voltages and currents present at the speaker.
7. Most tube amplifiers will have a main power switch and a standby power switch. To power up your amplifier first make sure that both switches are in the OFF position. Turn on the main power switch and then wait 30-seconds before turning on the standby switch. This allows the vacuum tube cathodes and heaters to reach operating temperature before the plate voltage (B+, high-voltage) is applied, which will prevent damage and extend the life of the tubes in amplifiers with solid-state rectifiers. If tube rectifiers are used, the plate voltage is delayed until the rectifier tube's filament warms up, so delayed use of the standby switch is less of a factor.
8. After power up, take a look at the output tubes through the rear ventilation opening of the cabinet. The output tubes are typically of type 6V6, 6L6, 6BQ5, 6550, 6CA7, EL34, EL84 or similar, and usually the physically larger tubes. The tubes should look "normal." Hopefully you have used the amplifier before and observed what "normal" looks like. On most tubes this is a typical orange colored glow from the heater or cathode. If the plate (anode) of the tube(s) are glowing red hot, it indicates a problem with biasing or elsewhere and the amplifier should be turned off immediately to prevent damage. Beyond the risk of damaging the tubes, operation with a glowing plate can cause damage to the expensive output transformer or other problems. When in doubt, have your amp checked by a competent technician. In any case, get to know what the normal operation of your tubes looks like, and get in the habit of checking their appearance with each use.
DURING USE OF THE AMPLIFIER
9. During use, have your amplifier positioned for good ventilation and cooling. Avoid placing the amplifier against a wall or other surface which would block air flow, and avoid being close to other heat sources.
10. If your amplifer has an impedance selector, such as used in some Marshall, HiWatt, Ampeg, and other models, turn the standby switch OFF before changing the impedance. Also, be sure to select the correct impedance for the type and number of speakers being used.
11. Since most amplifier failures occur during power up, make an effort to minimize the cycling of the main power switch. Instead, for brief breaks, use the standby power switch to turn off the plate voltage when guitars or effects are plugged-in, or during breaks in a set or practice session. You can leave the amplifier permanently on in the standby mode and then switch it fully on when needed. This will often increase the life of the amplifier components, although it will also waste electricity. Be aware of the tradeoff in amplifier life versus power usage and make informed decisions for your situation.
12. While playing through the amplifier pay attention to intermittent pops, crackles or the amp cutting in and out. It's important to get these diagnosed. It may just be annoying if it's due to the guitar input cable. If the problem is in the speaker cable then it could lead to real damage. If you hear the amp cutting in and out, reduce the amplifier volume and wiggle the speaker cable. If this changes (makes it happen more or stop) then stop using the amplifier until the cable is replaced. A speaker cable that is open or shorting may cause expensive damage to your amplifier.
13. Other than replacement due to failure, you'll want to change your power output tubes (typically 6V6, 6L6, 6BQ5, 6550, 6CA7, EL34, EL84) when you notice a change or dullness in the amp sound. Consult with a qualified technician to ensure that the change is due to normal performance degradation of the tubes and not some other problem. Pay attention to manufacturer guidelines for tube replacement, such as using matched or specially selected tubes, and for biasing with new tube(s).
14. Always follow the manufacturer recommendations for fuse replacements. If a fuse is blowing repeatedly it indicates a problem that needs to be fixed. Avoid the temptation to replace the fuse with a higher value as you will just allow the amplifier to operate with problem that is likely to cause further damage to the amplifier, or be a risk of overheating and/or causing a fire.
15. A fan blowing on the output section of the amp will keep things cooler and generally increase the life of the electronic components. The cooler the amp runs, the longer it will operate.
16. The power down process is the reverse of the power up. First, put the amp into standby mode by turning off the standby switch. Then turn off the main power switch. As mentioned above, let the amplifier cool down a bit before moving it so that it is less vulnerable to mechanical shocks.