At the risk of getting flamed by one particular fellow whose panties get quite wadded at the mention of Roger Modjeski’s name (apparently for not believing in the audible superiority of all audiophile boutique parts.), here’s what Roger found when he opened one of the eight Hi-Fi Tuning Fuses that were in one of his RM9 amplifiers returned to him for repair after the fuses had not done what a fuse is supposed to do when presented with a short: blow.
Roger discovered that the fuse was not designed for, capable of, or suitable for, use in a DC circuit---the very kind of circuit in which a tube operates. The customer’s RM9 had a tube fail, and the Littlefuse Roger installs in his amps would have done what a fuse is supposed to do when faced with a short in the DC circuit of a tube amp---blow. The Hi-Fi Tuning fuse did not, and the amplifier was then of course damaged. Not as a result of a fault in the design of the amp (unless you don’t want your tubes fused---Audio Research amps aren’t, ARC instead letting a resistor blow when a tube goes bad, thus requiring the resistor and any related parts to be replaced, rather than a fuse. At far higher cost, of course.), but because those fuses do not possess "high breaking capacity".
Surprised, Roger called first the U.S. distributor of the Hi-Fi Tuning Fuses, then the German designer/manufacturer. To his astonishment, neither knew what the term "high breaking capacity" means. That’s right---a fuse "designer" who knows less about fuses and their construction than an amplifier designer/manufacturer! The moral of this story is, if you are going to spend more on a fuse than a tube (if that doesn’t give you pause, spend on ;-), you might want to make sure the fuse is up to the task it is asked to perform in whatever application it is employed.
