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February 17, 2015

Amps › Repairs ›


Amp Tune Up Service

Guitar amplifiers work hard. Many are hauled around from show to show getting bumped and bruised. Some get drinks spilled on them. Some lay dormant in dusty basements for years at a time, while others are lovingly cared for and treated with the respect they deserve. Regardless of their lifestyle, guitar amplifiers are vital to a guitarist and need to be reliable when beckoned. They need to play sweetly whether in the studio, or in a dark club. And, like any other instrument, they need the occasional Tune Up.

What a setup is to a guitar, the amplifier Tune Up service at Chicago Music Exchange is to an amplifier. If your amp is sounding tired, or weak, if it needs it to be reliable for a gig, or it simply has not been played in years, a Tune Up service is the way to go to get that amp back in top playing condition.

An amplifier Tune Up involves going through the amp’s entire circuit to remedy any minor issues therein and give the amp a clean bill of health. This is to not only ensure the amp is working properly, but also safely. In this example we have an amp that was brought in to CME in working condition, but the client would like to have it Tuned Up.

Before working on any amplifier I always give it a good once over. I look for any obvious signs of trouble such as bad tubes, blown fuses, or an unsafe power cable. If all looks proper then it is time to open the amp up. Notice I have not turned the amp on. For that, I wait until a good look can be taken over the circuit itself in case there are issues that the player was not aware of. Once I have the amp on the bench I can assess the state that it is in. If all appears ok, I begin the amp Tune Up.

The first thing I do with an amplifier on the bench is to turn it on and listen. If all sounds normal without an instrument plugged into it, then I will play a few chords to get an assessment of the tonal condition of the amp. I will then go forward with putting signal through the amp via a signal generator, or a much more ear-pleasing way – just strumming a guitar. With signal flowing I poke all of the solder joints and move all of the wires individually with a non-conductive object such as a chop stick. I will know I hit a bad solder joint, or faulty wire if the guitar signal crackles, or drops out when i touch it. If this does happen the joint gets touched up, or the wire will be replaced. Often times solder joints on the tube sockets wear out from the history of tubes being plugged in/out causing those solder joints to move.

Voltage is what makes the amp operate and should be checked throughout the amp. Knowing what voltages are to be expected in the different stages of an amp, I use a multimeter and test various parts of the circuit. A few important places to check for appropriate voltage are the transformer leads, the tube sockets and the heaters.

Power tube bias is another very important item to check during a Tune Up. “Bias” is a term used to check the “idle” of how hot or cold a tube is running. Different tube types are comfortable at different bias points. Too hot a bias and the tube will live a short life, or overheat. Too cold a bias and your amplifier will sound lifeless and sterile. Set the bias just right and your amplifier will sound great and your tubes will live a long, happy life. It is important to note that one should always have their amp rebiased every time they replace their power tubes to ensure the tubes are producing the best tone that they are capable of.

There are many capacitors and resistors in a typical amplifier and they should all be checked during a Tune Up. Resistors tend to drift in value with age. Small drifts in value are ok and even expected, but large drifts in resistor values can greatly alter the performance of an amp. Plate load resistors, in particular, are quite susceptible to drift and should be checked and replaced as needed. The plate load resistors are the resistors connected to the plates of the preamp tubes. In other parts of the amp there are resistors that handle a lot of high voltage. These are paid special attention for any signs of wear since they get extremely hot when the amp is played and can thusly wear faster than resistors that handle less of a demand.

Capacitors also have a huge impact on a guitar amps performance. Coupling caps typically are used to sculpt the tone of a signal. They also block DC current from being passed further into an amps signal chain. If DC current gets into places it doesn’t belong then your amp will surely have noise issues. Electrolytic caps are an extremely important component of an amp. These parts handle the high voltage and filter ripple out of the alternating current (AC). When these caps begin to wear out, the amp will have an increase in noise or hum, possible ghost notes and a definite deficiency of punch and low end. As a general rule, the lifespan of electrolytic caps in a guitar amp fall around 15-20 years for optimal performance. After this time the electrolytic inside the caps begins to dry out and should be replaced. Our amp Tune Up service involves testing all capacitors to ensure they are performing properly.

With all of the circuit gone through and tested I want to make sure all of the pots and jacks have been tended to. These will be cleaned with a spray contact cleaner to ensure a scratchy-free operation and all of the screws and nuts in the amp will be tightened. The fuse(s) will all be checked to see that they are of the proper rating and the speaker will be examined for any punctures, tears, or wear. It will also be tested that the impedance of the speaker matches what the amp is set for.

Next I take a look at the tube sockets. These get cleaned using a spray contact cleaner applied to the pins of a tube and are then inserted in and out of the socket a few times to clean any oxidation that may have accumulated. The sockets also will be tightened, so the tube will sit firmly in place.

It is here that I will contact the owner of the amp and give any recommendations on things I may have noticed while going through the circuit. Are the tubes sounding tired and in need of replacement? Does the player wish to upgrade to higher quality resistors, or capacitors? Is the speaker the right choice for the tone the player is after?

With the amp all checked over and cleaned I put it back together and play it, giving it one final test that all is well with their instrument. The amp will now be performing better than when it came in and the player will have peace of mind knowing that his/her amp is in optimal condition for playing those sweet guitar tones.

If the notes a guitarist plays are his/her words, then the tones coming from their amplifier is their voice. A professionally executed amp Tune Up service from Chicago Music Exchange is a great first step in making that voice the best it can be. Your hard working amplifier deserves it.

Brian Carstens
Brian Carstens