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Rogue Eighty Eight fuse amperage?

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bamavette

bamavette

Member
Joined 2023
#1
I am working on a Rogue Eighty Eight amp for a friend and one of the output transformer center tap fuses is blown (yes I know why). It is a ceramic fuse and only has T250/450V on it, the T means slo-blow but without an A next to the 250 I cannot assume that this references the amperage. I think it just means 250 or 450 volts. If it is amperage it would have to be 250ma, which is kinda low for a ceramic fuse. There is one for each channel in series with the output transformer center taps and 500V B+.

So, does anyone know the value of this fuse?

Thanks.
 
#2
Since your Rogue 88 used a pair of 6550 or KT88 tubes, 250ma sounds about right for two tubes in PP class A1. They are usually biased at around 60 to 80ma each. So that's a possible 160ma quiescent at idle. Playing loud complicated music can come close to doubling that on peaks. I'd stick with ¼A slow blows. But you might want to risk 3/8A SB as a maximum.
 
#5
It's slightly unusual, but not totally. Probably depends on who made it and where it's made. I looked at pictures of the amp on line and it looks like a standard American 3AG size. Try carefully taking the bad one apart. You might be able to make an educated guess by looking at the guts. T doesn't seem like an American designation.
 
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#6
It is 3AG size, the amp was built probably 30 years ago. Taking it apart isa good idea.

On a separate note you should see the terrible diy work someone did on this. Oversized capacitors with leads 1mm apart, bypassed fuses, lifted solder traces, homemade cloth washers under the screws, bypass capacitors bypassed with more capacitors not tied down just laying under the pcb, exposed wires due to insulation melted from soldering tips. And some of the poorest soldering I have ever seen.
 
#7
Hummm, all 3AG size fuses I've seen are rated at 250 volts. That voltage refers to the arc over rating that happens when the burn out occurs. And it determines physical length and what, if anything, else is in the fuse body, like sand. If yours is rated at 450 volts that would explain the slightly unusual construction. However I've seen regular 3AG 250V fuses used as B+ fuses many times with no serious consequences. I even use them myself in my builds. But they probably wouldn't pass UL standards for a manufacturer.
 
#8
I took it apart and as thin as the wire was it 250ma seems quite reasonable. Nothing else in the fuse body either. I got the number for rogue audio, I will call them Monday and see if they will tell me. I have the schematic but there are no component values listed, and the fuses aren't drawn in either.
I have used 250V fuses in B+ lines my builds too, but that was for myself and I am repairing this for a friend and so I will be a little more careful. This amp already caused him a lot of problems due to the bypassed fuses.
I found this on Amazon of all places but it ships from overseas and will take a while so I may as well wait till monday and see what Rogue says.
https://www.amazon.com/gp/product/B01MS7GY5G/ref=ewc_pr_img_2?smid=A1GAO3IBXIZZNX&psc=1
 
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