How To Diagnose the Amplifier

Amplifiers aids in increasing the sound of an audio device or a musical instrument but it tends to develop some problems from time to time. The most common problem that faces amplifiers in failure to work is either sudden or gradual failures.

There are ways in which you can diagnose easily the amplifier. In order to do these, you need to do the following:

Check the fuse. The first thing that you must do is to take a look at the fuse and check if it’s blown. An amplifier’s fuse is usually located in the rear near the power cord. Unscrew the fuse and check if there are any burn marks. If you can see any blown marks, then it is an indication that the fuse has blown. When the fuse has blown, it is either the tube is dead or it’s dying and as a result, it forcibly draws a lot of power from the wall thus overworking the fuse.

You should also be careful when replacing the fuse of the amplifier. As a general rule, you shouldn’t attempt to replace a fuse with a much stronger one or this will result to a more permanent damage in the central power of your amp.

Check the tube. Tubes do wear out over time. Take a look at the tube and see if it is broken. A tube that is broken usually has white, black, or silver spots in its interior. In some rare cases, you will find that the tube has burned out. The tube burns like a light bulb. If it is in that case, it will usually have burn marks all over it. There are two types of tubes: power tubes propel signals out of the amp’s speaker while preamp tubes boost and shape the incoming signal. When the tubes have problem, a lot of inconsistencies may come about out of the sound coming out of the amplifier.


If the tubes are worse, you shouldn’t just replace a single one, you would have to replace all of them. The main purpose of this is to ensure that the power is balanced among all of the tubes. The same balance there are for the tubes will result to longer use of the tubes.

Turn on the amp. Turn on the amp and listen to the sound it produced. The tubes usually produce a dull sound. If you stay listening for about five to ten minutes and the sound suddenly goes away, it is an indication that the tubes are bad. But if the tubes are completely dead, the sound won’t go away.


Check the Capacitors. The other main components that don’t age gradually are capacitors. Many older capacitors typically found in the power supplies of tube amps are the “wet electrolyte” type. The material is a paste having some moisture content, which over time dries out, reducing the functionality of the device. This can result in increased hum, loss of low frequency response, low gain, and sometimes a phenomenon known as motorboating, in which the amp makes a continued popping or putting sound.

One of the functions of capacitors in tube audio circuits is as ac coupling or dc blocking between stages. A common failure mode in this application occurs when such a capacitor “leaks” dc, which upsets the operating point of the next stage. When this failure occurs and a capacitor feeds a pot, the presence of dc will cause the pot to scratch when adjusted, and the pot will not respond to cleaning and subsequently be damaged.

Check the Resistors. Usually pretty stable and reliable, resistors can be the cause of several problems. One of these is a crackling noise which results from moisture being trapped inside older carbon composition resistors (usually in the plate load position of the circuit). Replacement with a carbon or metal film type will cure this. Other resistor failures can be related to high temperature, over-voltage, or over-current, though most amps are designed with the components overrated for these 3 factors.

The transformer. The typical transformer fault occurs when a winding opens up, this is usually due to an over-current, over-voltage or overheating condition; less common is a shorted winding resulting from the same “over” conditions. Both are usually “indirect” failures, caused by something else (a tube, capacitor, wiring) failing and generating the initial fault. There are two repair methods for defective transformers; replacement or rewinding. Replacement is an option when an identical or very close substitution is available, but this may not be possible or desirable. Rewinding, though sometimes more costly than replacement, guarantees retaining the exact electrical specifications and physical dimensions of the original.

Diagnosing and possible fixing of amplifiers takes time and a lot of effort and as such, patience is greatly needed. Take your time in understanding some concepts. It’s much advisable to know how to fix things than to buy new ones.

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