Fitting internal fuses

Before replacing internal 20mm fuses in your equipment with our Russ Andrews Internal Fuses or Internal SuperFuses, ensure that it is disconnected from the mains supply.

Be aware that there are two types of internal fuses - type T (slow blow) and type F (fast blow). Check your original fuse before fitting; you need to replace your fuse with a Russ Andrews Internal Fuse or Internal SuperFuse of the same type. The value of the fuse will be stamped on it; you may need a magnifier to see it. Slow blow fuses will be prefixed with a T e.g. T 3.15A denotes a 3.15A slow blow fuse.

Only replace fuses on a 'like for like' basis. If your equipment is fitted with a 2A fuse, you must replace it with a 2A fuse. Fitting a fuse of higher or lower value may cause inferior sound quality or present a safety issue.

Internal fuses are found in three places.

1. The first is inside the IEC socket and is accessible from the outside of the equipment. First, remove the mains cable and disconnect the component from the mains supply. You will see the fuse holder underneath or to the side of the IEC socket. 

A small screwdriver is quite useful to pop out the holder so you can replace the fuse.


The value of the fuse can be found on the fuse holder or in the manual. 

2. The second place is a fuse holder mounted on the back panel. Again a small screwdriver is often useful to unscrew the holder. Please make sure the equipment is disconnected from the mains.

Removing back panel mounted internal fuse

Once the holder is loosened it will give you access to the fuse.


The value of the fuse is often printed on the back panel next to the fuse holder or in the manual. 

3. The last area is inside the equipment which will involve taking off the lid. Before doing so remember to disconnect your component from the mains supply.

Use an appropriate screwdriver to remove the screws holding the case to the chassis. The fuse is usually mounted before the transformer and usually mounted on the circuit board near the back of the IEC socket.

Equipment with lid removed

Simply remove the fuse from its holder and examine it to find its rating.


The value of the fuse is sometimes printed on the circuit board, or in the component's instruction manual. 

4. Often the only way to find the required information will be to take out the original fuse and examine the metal end cap where the fuse's specification will be stamped.

There will be a letter, either 'T' for Time Delay (AKA SlowBlow) or 'F' for FastBlow and then a number indicating the fuse value.

An example would be T6.3A which is 6.3 amp SlowBlow fuse. 

The information is often very small and difficult to read; the use of a magnifying glass will help. Some people use the camera on a smartphone to either take a picture and then zoom in or digitally zoom in while you’re holding the phone.