Please consult your unit's Owner's Manual to determine the correct fuse size (1/4" dia x 1 1/4" for instance), type (Fast Blow or Time-Delayed SLO-BLO), construction (glass or ceramic) and value (in Amperes) so that you are sure to order the correct fuse for your application. 

When replacing fuses, be sure the unit is powered off and unplugged from the wall and that the power supplies are discharged to reduce the risk of shock. 

Ceramic fuses have an opaque white body and must be measured from end to end with an ohmmeter if integrity of fuse is to be confirmed. An open reading of infinite ohms indicates a bad fuse. Glass fuses' bodies are transparent and you can usually see if the element is broken like a bad light bulb element. Or you can measure them with an ohmmeter. A dead short (reading < 1 ohms) read end to end means the fuse is good. Look around the circumference of the silver endcaps to read the AMP value of the fuse that you removed. 

Most Manley gear uses time delayed SLO-BLO type fuses 1/4" dia x 1 1/4".

MDL is the prefix for a GLASS bodied SLO-BLO fuse. Mains (power) fuses will be of this construction.

MDA is the prefix for a CERAMIC bodied SLO-BLO fuse. Power amplifiers B+ fuses will be of this construction.

Again, consult your unit's Owner's Manual to determine the correct fuse for your application. Failure to use the correct fuse can create a very dangerous situation, cause major damage to the unit, and/or burn down your house. Take this warning seriously.