A fuse is a piece of wire inside a glass or ceramic housing that is designed to break or blow if the current exceeds the stated amount. This is primarily to protect the person using the electronics to avoid an electric shock or fire. It is also to protect the electronics of a piece of equipment in the case something goes wrong i.e. a malfunction or a short circuit.
Wurlitzer 200 series amps have three fuses – one for the mains AC power supply and two for the speakers in the power amplifier section of the amp. The mains fuse in UK/Europe is a T250mA fuse and in the USA it is a T500mA fuse. It is important for the fuses to be slow-blow because the current the amp draws when it is first turned on exceeds the limit of the fuse. This means a fast-blow fuse will likely go straight away. The power amp fuses for the speakers are always 1.5A and should be fast-blow to protect the speakers.
A common cause of very bad distortion in a Wurlitzer amplifier is one speaker fuse having blown. This creates an imbalance in the bias of the amp which can hugely affect the sound. Replacing the blown fuse can often solve the problem.
In the image above are two old style types of fuses. They are sometimes known as pigtail fuses. When these blow they have to be desoldered and replaced. They are usually replaced with in-line fuse holders that make changing fuses much easier.
