UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

trobbins · 23rd Dec 2015, 10:30 pm

5x20mm fuses come with up to 500VAC rating - sure, 250VAC is most common, and the valve holder also needs to be equivalently rated (unless using an axial leaded part, which is pretty nifty, but again not too common). A secondary side fuse, even in the CT, has to have the same voltage rating as an arm fuse.

Given the amount of circuitry that is supplied from the diodes onwards, and the general reliability of modern ss diodes, I'd suggest that a CT fuse is an excellent choice compared to no fuse. If the equipment uses a valve rectifier, and each plate is additionally protected by an ss diode then that provides some additional assurance.

Some bias supplies are capacitively coupled off one side of a power transformer secondary V-0-V HT winding - they are susceptible to stress if a CT fuse blows, and so fusing the secondary winding arms would be appropriate.

23rd Dec 2015, 10:30 pm	#53
trobbins Heptode Join Date: Oct 2009 Location: Melbourne Australia Posts: 901	Re: Fuses 5x20mm fuses come with up to 500VAC rating - sure, 250VAC is most common, and the valve holder also needs to be equivalently rated (unless using an axial leaded part, which is pretty nifty, but again not too common). A secondary side fuse, even in the CT, has to have the same voltage rating as an arm fuse. Given the amount of circuitry that is supplied from the diodes onwards, and the general reliability of modern ss diodes, I'd suggest that a CT fuse is an excellent choice compared to no fuse. If the equipment uses a valve rectifier, and each plate is additionally protected by an ss diode then that provides some additional assurance. Some bias supplies are capacitively coupled off one side of a power transformer secondary V-0-V HT winding - they are susceptible to stress if a CT fuse blows, and so fusing the secondary winding arms would be appropriate.