Amp blows 5A plug fuses, why?

[Merton]

[quote name='TimR' post='845856' date='May 23 2010, 04:38 PM']Yes VA is Watts in this case. I'm guessing that the transformer has to be rated higher than the power amp and from what I've read it is the transformer rating that governs the inrush current, not the power amp rating.

Anyway, I posed a Q on the Warwick support forum. Its Sunday in Germany so I guess all their designers are out in the sunshine on the Nurberg Ring in their Porches. Hopefully,knowing their efficiency, they will reply at 8.01 tomorrow morning.

[url="http://forum.warwick.de/20-warwick-amp-customer-support/11987-pro-fet-5-1-fuses.html#post185930"]http://forum.warwick.de/20-warwick-amp-cus...html#post185930[/url][/quote]
And tomorrow is a public holiday over there so don't expect anything til tuesday!

[discreet]

TimR, await the answer to your Q to Warwick with bated trousers.

Meanwhile, my 13A cable with 7A fuse continues to do its job... will post if it goes tits-up.

Many thanks to Ian Savage, who not only sent me a 10A fuse, but also a 10A-rated cable PLUS two spare 6.3A slow-blow fuses for my amp... above and beyond the call of duty mate, thanks again!

[TimR]

I have recieved a reply, not the correct one so I have clarified my original question.

Never put a glass fuse in a plug top! The standard cartridge fuse is sand filled.

Put one of those screwdrivers with an LED in it that shows contiunuity in your gig bag. You can use that to check the fuse. Porsonally I just take a spare lead. I don't really want to be standing around changing fuses at a gig.

[TimR]

I did some more thinking. In Europe they don't fuse the plugtop. I'm sticking with the 13A and a heavy duty lead. The T6.3A is enough to protect the amp.

[discreet]

[quote name='TimR' post='849186' date='May 27 2010, 09:36 AM']In Europe they don't fuse the plugtop. I'm sticking with the 13A and a heavy duty lead. The T6.3A is enough to protect the amp.[/quote]

Ha! I came to the same conclusion. ^_^
My 10A/7A combo seems fine, but I have a heavy-duty lead with 13A fuse which I'm going to carry as a spare.
I'm also carrying spare T6.3A amp fuses and 7A, 10A and 13A plug fuses.

Which hopefully should cover most eventualities! Except for a power cut, obviously.

[Ian Savage]

You're right in saying that the Europeans (and indeed our colonial cousins) don't fuse the plug, but that's because they don't have an earth connection in the plug, so it'd be pointless.

The fuse within the amp is the one there to protect the amp from power spikes and suchlike, the one in the plug is designed to blow should the amp develop a fault and start dumping unusual amounts of current to ground. This shuts the whole thing off and prevents you from getting a shock should you touch exposed metal on a faulty unit; it's actually worth finding out exactly what you should be using from the manufacturer IMO, just for that extra bit of safety, but with Warwick being European themselves they might not be totally au fait with it.

[discreet]

[quote name='Ian Savage' post='849202' date='May 27 2010, 09:56 AM']it's actually worth finding out exactly what you should be using from the manufacturer IMO, just for that extra bit of safety, but with Warwick being European themselves they might not be totally au fait with it.[/quote]

I agree, but TimR's question was not adequately answered on the Warwick forum... because it seems Warwick (and probably other European manufacturers) are blissfully unaware, or just disinterested, in UK plug fuse standards, and therefore don't have any tech information about them. Even though presumably they must have to provide fused mains cables for the UK market - or maybe these are provided by a third party, which may be where the problem lies.

I'm assuming that any plug fuse that's rated high enough to 1) protect the mains cable and 2) not blow under power-on stress, will be pretty much OK as the amp itself is protected by its own internal fuse.

[discreet]

Sent this email to Warwick this morning:

'I've had a problem with blown fuses (5A mains plug fuse, not T6.3A amp fuse) and would like some information:
Do you supply fused mains cables for your equipment sent to the UK, or is it a third party?
What rating are the plug fuses supplied with mains cables for the UK market?'

To which I quickly got this reply:

'We do supply cables for UK equipment. Their fuses are T13A.
But they can only be ordered by a listed music shop.
Mit freundlichen Grüßen,
Warwick GmbH & Co Music Equipment KG'

So I Googled 'T13A fuse' of which this link is an example:

[url="http://www.analogueseduction.net/product/Furutech_T13A_Mains_Fuse_FURU-13"]http://www.analogueseduction.net/product/F...ns_Fuse_FURU-13[/url]

FIFTY-FOUR POUNDS NINETY FIVE???!!! What's going on there, then?

It must be the 'increased power, dynamics and resolution' that you get from this fuse! Now we're well into Hi-Fi fantasy land!

[Ian Savage]

[quote name='discreet' post='849410' date='May 27 2010, 02:01 PM']So I Googled 'T13A fuse' of which this link is an example:

[url="http://www.analogueseduction.net/product/Furutech_T13A_Mains_Fuse_FURU-13"]http://www.analogueseduction.net/product/F...ns_Fuse_FURU-13[/url]

FIFTY-FOUR POUNDS NINETY FIVE???!!! What's going on there, then?

It must be the 'increased power, dynamics and resolution' that you get from this fuse! Now we're well into Hi-Fi fantasy land! [/quote]

The '13A' bit is self-explanatory, the 'T' simply stands for 'Time Delay' (it's actually something elese in German or something originally, but we English-speakers have substituted it), as opposed to 'F' for 'Fast-blow'.

That kind of audiotardary beggars belief - IT'S A TINY BIT OF WIRE, FFS!

[TimR]

Sorry Ian, I don't fully agree.

the fuse in the amp is a time-delay and looking at the current/time curves for a normal 13A normal and a T6.5A there's really not that much in it.

The mains fuse would also blow under live-neutral fault.

The chances of a live-nutral or earth-live fault developing that would leave a fault current that would blow a 5A fuse but not a 13A fuse and hence lead to an electric shock risk are extremeley low.

Fuses should not be seen as protecting human life. Fit RCDs if that's what you want. ALL fuses are there to stop your gear from turning into a fireball.

In this case the time delay fuse is fitted in the IEC socket on the chasis amp, so the only thing the mains fuse is protecting is the mains lead.

The main point is that the plug top fuse must not be sized bigger than the mains lead is rated at. So 13A should not be put into a 0.75mm2 cable. I think that the earlier discussion on 3A 5A and 13A fuses becoming the norm is that it is increaslingly common for all electrical equipment to be fused at the chasis and the only size cables in common usage are now either 0.75mm2 or 1mm2. 7 and 10 fuses are essentially redundant.

[TimR]

Missed the two replies.

No point in puuting T13A in the lead as the T6.5A in the chasis will blow first.

Mad.