What common issues come up when building a valve guitar amp?

As Lamington amp builders progress through the construction of their amplifiers, some common questions arise. I thought it might be helpful to discuss some of these questions to assist other diy amp builders.

The first issue that often comes up is identification of the components. For a newcomer, it can be confusing to identify capacitors, resistors, diodes …… picofarads, microfarads, megohms etc!

The first step is to identify the resistors. They look like this:


You can see that most resistors have their value marked with a colour code. To “read” the value of a resistor, here is a colour code chart:



Another issue that arises in amp building relates to layout and wiring.

From time to time, I am contacted by builders of my Lamington amps who report that their amp works but has noise or other extraneous hash in the output. When the volume is increased a whistling or rushing sound is heard. This is almost always caused by layout and wiring issues. What is not immediately evident in an amp is that the most sensitive parts of an amp can pick up the large signals around the output stages. If the wiring in the amp is not short and direct output signals get picked up by the input stages causing instability and oscillation much like when a microphone is placed too close to a speaker in a PA system. If your amp demonstrates these symptoms, spend time shortening unnecessary long leads. This will sort out the issue in 95% of cases.