[fbny71]

One of my 7Bs is blowing fuses:



Not sure if the replacements I got are the right ones, they blow right away too:



This is the spec for the fuses printed on the back panel:

[ragg987]

Your replacements are rated 3A. Far too low for this amp, plus you are using a fast blow fuse which will probably blow due to current inrush at switch on. Just as a comparison, my 4BSST requires a 6.3A slow blow fuse at 240v (I am in the UK). Looks like you are 120v mains, so you will need a higher rating. What does the original fuse say, usually marked on the cap. Or compare it to the working 7b? The 3AG7A marking suggests 7A?

Once you get the correct fuse, and if it still blows, you need to check the amp out as something is not right.

[fbny71]

What does the original fuse say, usually marked on the cap. Or compare it to the working 7b? The 3AG7A marking suggests 7A?

The writing etched onto the sides of the caps is too light, too faint, I can't read it. I am going to try amplifying with a USB microscope, hopefully that will get me a better look.

[fbny71]

I'm seeing 7A 250V 312 on one of the caps.

First search, I find this on Amazon:

[ragg987]

7A agrees with case marking. Can you see a 'T' marking on the fuse? This would indicate slow blow Vs the fast one you found on Amazon. Not sure which is correct.

[fbny71]

Would that be located on the flat part of the plate covering the diameter of the tube? I don’t remember seeing it in the sequence of characters inscribed on the part of the metal that goes around the tube.

[fbny71]

I see what looks like an L and an F superimposed over each other.

[fbny71]

I hadn't heard back from Mike yet so I went ahead ended up getting these 7A 250V Slow-Blow fuses:


Everything is working now but I am concerned, they did't look like the fuses there already so I replaced all four, two each in each 7B.

Top fuse is the original:

[Ron D]

I am not an expert but they look too dissimilar to be a match. If your new one is a slow blow 7A and by the looks of the original 7A fuse it is a fast blow fuse - visually comparing the width of the fuse metal inside.

Hopefully someone more learned will chime in.

[fbny71]

I’ll order a set in fast blow as well.

Hopefully someone does chime in, but I’ve been without sound too long and I’m going to carefully use it as currently set up for the time being.

[James Tanner]

Hi

I asked Mike to have a look at this for you.

james

[fbny71]

It doesn’t have to be Mike if he’s too busy; I’ve emailed him a couple of times since the end of March and hadn’t heard back. Now that the amp seems stable with the new fuses, I’d be happy to buy several directly from Bryston at the correct spec.

[Anonamemouse]

Nobody is curious as to why the amp is blowing (apparently) multiple fuses? Just put in a new one and wait until it blows too?
A fuse blows for a reason. And replacing a 7A FASTblow with a 7A SLOWblow... You could just as well insert a solid nail. It's just as "safe".

[fbny71]

One of my 7Bs blew one of the two fuses.

The same amp blew the replacement fuse which I incorrectly bought at 3 amp misunderstanding the way the fuse spec was written.

When I replaced them with the 7A slow-blow, it’s been working without issue. I also ordered 7 amp fast blow to see if there is any difference.

I’m hoping that Bryston will provide me with the the proper spec to make sure I’m using the correct fuses.

[fbny71]

And now I've replaced the fuses with the fast acting ones I received today and still good.

Again, these don't look the same either, the fuse on top is the original:



But, seeing as the amp is working correctly, I'll leave the fast acting ones in until/unless Bryston tells me otherwise.