When you repair an amplifier, you have two choices. You can bring it back to its original state by fixing only what is broken. Or, you can improve the circuit by modding it.

There is a lot to love about an amplifier that is in fully-functioning, but original, condition. When using a vintage amp, you are playing music on a slice of time. You are combining two different musical periods in a way that is impossible to replicate with any other gear. It’s basically time travel.

If your tube (or solid state) amplifier is not “turning on,” the cause of this problem could be a blown line fuse. The line fuse, also referred to as a mains fuse, is the fuse that stands between the main AC power and your power transformer. In an otherwise functional amp, the main fuse can and will blow when there is a problem between the wall outlet and your power transformer (PT). A fuse can also blow when there is a short somewhere in the amp. In either case, the fuse is doing its job when it blows and is protecting the amp by stopping it from running when there is a problem present that could harm the amp’s circuit.

All tubes follow the same basic principles. Inside a tube’s glass enclosure, you have 1) a vacuum and 2) at least two electrodes (but often more, depending on what type of tube we’re talking about). Each electrode has a specific job: either releasing electrons, attracting electrons, or slowing down or speeding up the flow of electrons. We’ll talk about these jobs later. For now, the main thing that tubes are intended to direct electrical current from A to B in some way that is useful to the circuit.

Tube amplifiers (and many solid state amplifiers) contain high voltages. Like any reasonably dangerous household object, you should certainly respect your tube amp. However, you don’t have to be afraid of it. If the amp is unplugged and the chassis is screwed in, it is safe to perform basic maintenance like replacing mains fuses and swapping tubes. In fact, fuses and tubes are accessible from the chassis because they are intended to be replaced by the user.

If your amp makes no sound, it is first important to define what you mean by “no sound.” To that end, the first test you should perform is whether you can hear anything coming from the speakers. (This is, of course, after you have eliminated the possibility of trivial problems.)

Listening to what (if anything) comes out of the speakers can help you isolate the problem to specific parts of the circuit. If you hear no sound coming from the speakers — including hum, hiss, reverb crash, input cable pop, or any other incidental, non-musical sounds — the problem could be the speaker itself. But, if you hear non-audio sound coming from the speakers, the problem is likely, although not guaranteed, to be a fault in the preamp section of the circuit.

If your amplifier isn’t working, the best thing you can do is describe the problem as accurately as possible. If you’re into DIY, using accurate terms will help you google your problem and give you the best search results. If you’re asking a tech or a friend for help, describing your problem with specificity helps them offer more relevant suggestions.

The filter capacitors in many amps are mounted in a metal can, which can be an obstacle to successfully recapping the amp. These days, filter cans are only made in a limited values, so it's hard to find the exact match. Mounting the caps outside of the can is another option, but finding the space can be tricky. Removing the can can leave a giant hole, which can allow dust to enter the chassis over time. So, what's the best way to replace can-style filter capacitors?

In Part I of our guide on fixing hum, we listed some easy fixes. In Part II, we’ll go into further detail on techniques that require some prior electronics experience to execute. It’s worth checking out Part I first, because it listed some simple, non-invasive things that you should always be tried before diving into the amplifier’s circuitry. For the purposes of this article, we’ll assume that you already tried everything in Part I. This includes:

The heaters of your vacuum tubes are one of the most critical parts of your amplifier. A well-designed heater circuit is quiet and unobtrusive: truly an unsung hero of any quality amp. On the other hand, flaws in a heater circuit can produce noise.

Wurlitzer tube amps are in fact very similar to guitar amps.

But before we talk about that, let’s back up a little. The Wurlitzer itself is very analogous to an electric guitar: the heart of both instruments is a pickup that converts vibration into an electrical signal that is ultimately sent to an amplifier. In a guitar, the amplifier is almost always external, but a Wurlitzer’s amplifier is tucked into the body of the instrument.

This Wurlitzer 120 arrived in exceptional condition. It had spent many years studio, a carpeted, finished basement housing an enormous collection of jazz records. Really the only indication that this keyboard is a late-50s vintage is the splatter-paint finish. It doesn’t show any of the cosmetic wear that you’d expect from a 60-year-old piece of gear. There’s a little bit of dust in the cheek block tolex, a little bit of patina on the metal parts, and that’s it.

A widowmaker amplifier has no power transformer or fuse. Instead, the two-prong, non-polar power cord is wired directly to the rectifier tube. It is very unsafe, because under even minor failure conditions (such as a shorted capacitor or even - in some models - plugging the power cord in backwards), the mains voltage might end up on the guitar strings and the user will be shocked/electrocuted.

On the plus(?) side, power transformers are expensive so widowmaker amps could be manufactured and sold at a lower price. This ensured that every aspiring guitarist in America could own a low-fi death trap if that’s what they really wanted.

At Tropical Fish, we are pro-electronics safety. We don’t want anyone to get hurt working inside a tube amplifier. At the same time, we hate to see people writing online who overstate the dangers of working on a tube amplifier. It really seems like certain factions want to discourage people from opening their amps up at all. This is a bad thing.