11-17-2017, 02:22 PM
A few things to keep in mind when sizing up a fuse: (and yes, for regular radios, up to 7-8 tubes, I also use 1A fuses)
1. A fuse is not there to protect your equipment, it is to protect you and your property from the equipment.
2. There is no such thing as exact value you should be using - it is always a compromise.
3. A fuse loaded up to and some 80% above the rated value does not blow, slo-blo or fast acting. Reliable blow-up from 1 to 10s occurs at 2-3 to 5 times the rated current.
Now, as long as your wires are thick enough and do not start going on fire before your fuse blow it is OK to have a higher value fuse. The wires of AWG 20 which many of us use are good up to 11.5A of normal operation, and then some.
Components when blow might release the smoke but rarely will draw enough current to blow a fuse, even properly sized.
In the transformered radios except the primary of the transformer and the filter capacitor (back in the days - today the safety caps are guaranteed to fail open) there is little that could cause a fuse to blow. And what can blow the fuse (the primary short or something very bad on the secondary side - in a regular radio I am not even sure what) will create currents that will blow 1A fuse as well as 2A fuse, as well as 3A fuse.
So, for a small table radio 1A is good, even a Slo-Blo, plus it will withstand the accidental transformer saturation (which Russ mentioned) and for a 37-116 or 37-690 2A fuse if good.
Again, a radio is not a constant power device so if the AC voltage goes down it does not mean the current will go up - no, it will also go down, proportionally more or less.
Those who want to protect as much as possible could try to install the fuses of smaller values commensurate with the current they protect after the transformer, like protecting filament winding or B+, (Philco used a fuse protecting the B+ feeding the output audio transformer, not that it helped much) but that could be tricky and all kind of scenarios should be considered. I would not do it.
1. A fuse is not there to protect your equipment, it is to protect you and your property from the equipment.
2. There is no such thing as exact value you should be using - it is always a compromise.
3. A fuse loaded up to and some 80% above the rated value does not blow, slo-blo or fast acting. Reliable blow-up from 1 to 10s occurs at 2-3 to 5 times the rated current.
Now, as long as your wires are thick enough and do not start going on fire before your fuse blow it is OK to have a higher value fuse. The wires of AWG 20 which many of us use are good up to 11.5A of normal operation, and then some.
Components when blow might release the smoke but rarely will draw enough current to blow a fuse, even properly sized.
In the transformered radios except the primary of the transformer and the filter capacitor (back in the days - today the safety caps are guaranteed to fail open) there is little that could cause a fuse to blow. And what can blow the fuse (the primary short or something very bad on the secondary side - in a regular radio I am not even sure what) will create currents that will blow 1A fuse as well as 2A fuse, as well as 3A fuse.
So, for a small table radio 1A is good, even a Slo-Blo, plus it will withstand the accidental transformer saturation (which Russ mentioned) and for a 37-116 or 37-690 2A fuse if good.
Again, a radio is not a constant power device so if the AC voltage goes down it does not mean the current will go up - no, it will also go down, proportionally more or less.
Those who want to protect as much as possible could try to install the fuses of smaller values commensurate with the current they protect after the transformer, like protecting filament winding or B+, (Philco used a fuse protecting the B+ feeding the output audio transformer, not that it helped much) but that could be tricky and all kind of scenarios should be considered. I would not do it.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
