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Basic Tube Amp Maintenance

 

In this tutorial i'd like to talk about simple tube amp maintenance. Although tube amps are said to be difficult and costly to keep, these tips will make things easier.

 

The difference in reliability between solid state (transistor) amps and tube amps is mostly in the tubes themselves. In 9 out of 10 times you will encounter a problem with a tube amp there will be something wrong with one or more power tubes in the back of your amp. In some cases there will be something wrong with the smaller pre-amp tubes.

 

Tubes need replacing

If you are regularly playing your tube amp, it's a good idea to replace the power tubes once a year. Replace the pre-amp tubes every 5-7 years or so. Tubes wear out and become more vulnerable over time which is why they need replacing.

 

What if my tube amp stops working?

If there is something not right with how your amp works, like crackling sound, no sound, very low volume sound or anything like that, the first thing to check out is whether or not the power tubes are broken. Any small crack in the tube glass enclosure or any problem with the tube electronics can cause these problems. Cracks or other problems can be causes by handling, lifting and placing the amp while the tubes are still hot, so ALWAYS switch off after playing and allow your amp to cool down for about 15 minutes before picking it up!

 

tube amp maintenance sovtek power tube 6l6gc
A Fender-picked 6L6GC power tube in its socket.

Look closely at the power tubes while the amp is on standby. Is there a difference in light between them? Is there an alarming smell? Switch on the amp, turn up to half volume and tap the power tubes one by one with a pencil, lightly. This should only result in a very soft tap sounding through the speaker. Anything louder than that and that tube is surely broken. Consider replacing ALL power tubes (the big ones) if any of this is the case. Find out which power tube type your amp uses by writing down the numbers and type written on the power tubes. The guitar shop people will know which tubes you need when they see the number and type.

 

Power tubes need biasing in some cases when put into an amp. This is something best left to a specified amp technician. However, a lot of tube brands offer pairs of power tubes that are 'matched' meaning they have the same bias value. In some cases, you could safely replace your power tubes with these 'matched pair' power tubes without biasing and the help of a technician. Some amps, like Mesa Boogie tube amps, have something called auto-bias and do not need biasing.

 

How to replace all power tubes or all pre-amp tubes

Here's how to replace power tubes. Switch off the amp entirely and allow the tubes to cool down for 5 minutes. Now take out the power tubes from the amp like this. Take a soft piece of cloth in your hand so you're not touching the glass directly, grab the power tube lightly and wiggle it slowly while gently pulling it down, out of it's socket. Do this also for the other power tubes.

 

Now, using the same piece of cloth, hold the new tube and turn the tube so that it is aligned with the little holes in the tube socket. Gently push the tube's foot in the socket for 1/8 inch or 2 mm, this should be easy so make sure it's aligned properly. Wiggle the tube sideways gently, while pushing it into the socket further. Careful. There you go, power tube installed. Do this as well for the other power tubes.

 

Switch your amp on standby, let it warm up for 5 minutes and switch it on. Check if the problem is gone. If the same problem is still present, there is a big probability that it's in the pre-amp tubes. Replace the pre-amp tubes in the same manner as the power tubes. Pre-amp tubes are smaller and more difficult to reach inside your amp, so be careful. When you've replaced all the tubes this way the problem should be gone and the amp should be working as normal. If not, take your tube amp to a qualified technician (your local guitar store will know one) and have them repair it.

 

"If there are four power tubes they are often in matched pairs - inner pair, and outer pair. Replace the inner pair, then the outer pair, rather than go left-to-right." -Micky Z

 

How to replace just the broken tube

If you do not want to replace all power tubes at once (because they are costly), switch off the amp and replace one power tube. Start with the one on the left. Switch to standby, let the amp warm up, switch on and check if the problem persists. If not, the original tube was broken. If the problem is still there, switch off, put back the original tube and replace the next tube.

 

Continue like this until you've localised and replaced the problematic tube. Remember that the new tube is not matched with the original tubes. This could result in a less good tone from the amp because the amp is not biased and the tubes do not match. If the amp still sounds ok for you, don't bother and leave it like that!

 

How can i fix dials/potmeters that crackle or noisy dials?
After some time (a few years), most potmeters will become noisy and start to crackle. This is due to dust and dirt inside the inner mechanics of the potentiometer.
It can be easily fixed by spraying in a product like 'Stoner Electrical cleaner', 'DeoxIt' or 'Kontakt Spray'.
Pull off the knob itself, gently. You'll see a little metal ring around the foot of the turning screw. Spray some of the cleaner in between the ring and the base. If there is a little hole in the base ring or otherwise, it's for cleaning purposes, so spray some into that hole.
Now, twist the meter back-and-forth as far as it can turn, about 20-30 times. This should fix the crackle/noise problem!!


There you are, the basics of tube amp maintenance. As said, leave anything beyond tube or potmeter problems to a technician and you'll be fine!

 

 

Contributing artist:


Micky Z
(rock)

http://www.bandmix.com/mickyz/

 



tube amp maintenance fender 57 amp