You may have just had your amp serviced with fresh tubes,  just spent good money on a tube amp, or just want to know how to make the tubes last longer. These tips and rules are something that every tube amp owner should know and follow.

 Connection / Hookup

 For amps with separate heads and speaker cabinets, or “stacks”: Make sure that you use speaker cable to connect the cabinet(s). NEVER use a shielded guitar, instrument or line cable to connect speakers! Shielded “guitar cables” have a very small inner wire that is wrapped with a shield to carry the low level signal from your guitar. When used as a speaker cable, this cable will not allow all of the power from the amp to reach the speakers, and will actually “deflect” some of the power back to the tubes and output transformer which can eventually damage them. In some cases, shielded cables can actually melt and short out, causing severe damage to the amp.

 Always make sure that you use a “Speaker” cable for the speakers, and a “Guitar, Instrument, or Line Cable” for everything else. Use a quality speaker cable that is as short as possible to let all the power through.

The next thing is make certain the impedance setting is correct. The amp head, and the speakers each have an impedance number that is stated in ohms. This is an electrical term that is basically how much of “load” the speaker is on the amp. Most amps have a method of selecting the ohms or impedance to different settings, and it is critical that the “ohms of the amp” MATCH  the “ohms of the speaker(s)” !

 If you have a stack setup, start by looking at the back of the speaker cabinet. The impedance number should be listed on the back. Most cabinets will have an 8 ohm, or a 16 ohm rating. Most Marshall cabs will be 16 ohms, most Mesa or Crate cabs will have an 8 ohm rating.

If the cab says 8 ohms, then set the amp to 8 ohms as well. If the cab says 16 ohms, then set the amp to 16 ohms. Some amps have different output jacks labeled with different impedance numbers, so if you have an 8 ohm cabinet, plug the speaker cable in to the 8 ohm jack on the amp…etc. Some amps have a switch that you can set to match the numbers.  You are just looking for them to match up.

  An unmatched setup will not allow the amp to produce full power, and will strain the power tubes and transformers. You will get full power, tone and tube life only if the amp matches the cabinet at all times.

  Most tube combo amps have the speakers and amp matched from the factory and you don’t need to ever change this, unless you add or change speakers.

 If you add or change speaker setups, you will need to change the amp settings to match. It can get a bit complicated figuring out the total impedance of multiple cabinet / speaker setups but in general……if you use two 16 ohms cabinets, you set the amp to 8 ohms. If  you use two 8 ohm cabinets, you will need to set the amp to 4 ohms. Always check to see if this is set up correctly before playing your amp. Look it up in the owners manual, or call or email me with the information. ( You still have the owners manual….right? )

 NEVER use a tube amp without speakers connected.  Some people have tried using the amp’s line out for recording and run the amp with no speakers connected. This is the worst mismatch you can make. A tube amp MUST have speakers connected to it, or it will damage the tubes and output transformer. Besides, you will find that you get better recording results by placing a mic on the speakers. We can modify your amp to operate as a tube preamp, but unless your amp is set up this way, always play it with a speaker properly connected.


 Use the standby switch correctly.

 Most high power tube amps have a power switch, and a standby switch. Proper use of the standby switch can greatly increase the tube life.

When you first turn on a tube amp, the insides of the tubes are warmed up by a heater, called the filament, inside the tubes.  This heater generates the flow of electricity inside the tube, and takes a short time for it to come up to full strength.  Tubes also require a high voltage power supply to make the flow work. The standby switch turns this high voltage supply to the tubes off and on. It is much easier on the tubes if the heater comes up to strength before the high voltage is applied to them. This way, the tubes are “warmed up” before they are hit with high voltage and audio signals.

 When you first turn on your amp, switch the power switch to “on” with the standby switch set “off”, or in the standby mode. Wait a few moments for the tubes to warm up, usually 30 to 45 seconds is fine. Then turn on the standby switch, and you are ready to play. Following this method can greatly increase the life of the tubes. When you take a break, turn off the standby, leave the power on, and just turn the standby back on when you are ready to play. If you need to leave your amp for more than say…30 minutes, it would be best to shut the amp completely off.

 When you shut the amp off, you can simply turn off both power and standby switches at the same time.

  It is also important to note the airflow around your amp, whether it is onstage, in the studio, or at home. Amps have ventilation grills and openings around the cabinet. Airflow for the tubes is very important… they run really hot. Make sure that the ventilation openings are not blocked by having the amp pushed up against the wall or a curtain, etc. You should not block off the top vents on your amp by setting other equipment on top……and never…I say NEVER set drinks on top of your amp.

 Transportation and Storage

 When you are not using your amp, or any electronics for that matter, keep it covered and keep it clean. Use your amp covers, or even some towels. Dust and dirt can dramatically shorten the usable life of amps, so keep it clean, and care for it. A dirty amp can develop bad distortion, noise, loss of power, controls that cut out, and tone that wavers. Never store your amp in dirty surroundings. Keep it inside if possible, in a clean environment, and keep it covered or in a road case.

  All electronics, including amps should be stored in places with temperatures where people would be comfortable also. They do not like temperature extremes any more than you do.

Traveling with amps can often mean leaving them out in the truck overnight in winter temperatures. When your amp is exposed to this cold, you should plan on letting it warm up to room temperature before turning it on. Tubes do not like to have their heaters lit when they are freezing cold. The other potential problem that occurs during cold weather is water condensation. If you take your amp out of a cold truck and open to room temperature, it will often get soaking wet inside from water condensation. Watch out for this and allow time for your amp to warm up and dry out slowly before turning it on.

 When transporting a tube amp, always leave the amp standing up, in the playing position, so that the tubes are vertical. Laying your amp down flat, with the tubes horizontal can cause the tube base to break during transport. There is also the possibility of loose items like cables and pedals in the back of the amp breaking the tubes by hitting them. Give your amp a gentle ride, up in the front seat instead of in the truck bed for example.

If you plan to travel or hit the road at all…..don’t even consider starting out without your amp in a road case.

 Tube amps can be fairly fragile items, but with the proper care and thought, they can be made to last much longer with fewer breakdowns and damages.

 Tube Type / Amp Type

 The life of your tubes depends on the type of amp as well. Circuit design and tube type play a role in how long the tubes will last.

 6L6 type power tubes will generally outlast the EL34 type. Amps that do not have the bias calibrated correctly can burn through tubes much faster than one that is setup properly. Certain amps will use up tubes faster than others due to higher voltage designs. Lower powered “Class A” design amps can use up tubes much faster than higher powered amps. Class A amps run the power tubes at full power, all of the time.  They are generally designed to run the tubes right at the maximum power spec, and they often use smaller, less robust tube types. It seems backwards, but these smaller amps may need the tubes replaced much more often than higher powered, more expensive amps.

 We have the experience to choose the right tubes for your amp and set them up properly so you get the best tone, best reliability, and longest life from your amp. We can also convert your amp to use a different tube type for longer life and different tone.

  A little care, thought, and routine maintenance can go a long way towards keeping your tone at its best and keeping your amp running longer.

  Call or email me with any problems or questions.....

 Mike Metz / owner : Thesis Audio Service



Tips for caring for your tube amplifier and helping the tubes  last longer….