mains fuses

camf

Something i've never thought of before... what's the correct mains plug fuse for an amp? Is 3, 5 or 13amps? And are the standard ones okay or am I better with the hand-wired ones?

Cheers,

cam f

mart

3 amps on a 230 volt supply gives nearly 700 watts. So, even allowing for some inefficiency, unless you are running a very big rig indeed, that will be enough. 

 Hand-wired is better, of course.

ecc83

In my experience when the KT88s go ape-shit in a 200watter they take out HT, amp mains (3.15A) AND 13 amp plug fuses! 

The fuse in the plug is there JUST to protect the IEC lead or fixed mains cable. Now IEC leads are actually rated at 10amps max but a 13A fuse is perfectly proper in this instance. Only very low powered devices such as line lump power supplies (e.g. the old HT pedal AC jobbies) should have a 3 amp fuse because they use a twin mains cable rated at 6amps or so. 

That would be "Da Law" but in practice even a 5/6A rated mains cable will easily carry the fusing current to blow a 13A plug fuse....

You should all TF! We live with such safe and conservative electrical regulations in this country!

Dave.

ICBM

ecc83 said:

You should all TF! We live with such safe and conservative electrical regulations in this country!

Now, yes .

I was just looking at an old valve radio the other week, and you can guess what type of power supply that had .

@camf - Dave is right, it doesn't really matter for an amp. The amp's internal mains fuse will certainly be a lower value, so in theory the one in the plug shouldn't come into it. 3A for anything that doesn't draw more than 700W or has a 'flat' 2-core cable, 13A for everything else covers it.

ecc83

"I was just looking at an old valve radio the other week, and you can guess what type of power supply that had "

Was it an AC/DC jobbie with droppers in it for the heaters and a chassis (hopefully!) connected to incoming neutral? 

Or! Was it one of the even older, SUPER dangerous "line chord" examples?

Fixed 'em all including the tellies with the chassis at 1/2 mains no matter what!

Dave.

ICBM

AC/DC job with a reversible 2-pole plug at the radio end so you have a 50% chance of the chassis being live .

ecc83

ICBM said:

AC/DC job with a reversible 2-pole plug at the radio end so you have a 50% chance of the chassis being live .

Noice!

Dave.

ICBM

And of course no fuse in the thing at all... nor in the mains plug, originally - round pin.

Sometimes all this modern regulations stuff is a very good thing! (Even if a few if them do go a little over the top now.)

ESchap

ICBM;200723" said:

And of course no fuse in the thing at all... nor in the mains plug, originally - round pin.

Sometimes all this modern regulations stuff is a very good thing! (Even if a few if them do go a little over the top now.)

Oi!! It's now fused and the chassis permanently attached to neutral ... Safe as ... A safe thing now B-)

ICBM

ESchap said:

Oi!! It's now fused and the chassis permanently attached to neutral ... Safe as ... A safe thing now B-)

Good work .

Now remember to keep that fire extinguisher to hand .

ESchap

ICBM said:

ESchap said:

Oi!! It's now fused and the chassis permanently attached to neutral ... Safe as ... A safe thing now B-)

Good work .

Now remember to keep that fire extinguisher to hand .

Got the fire extinguisher already ..... all those dodgy old restored amps I have .... 

Decided with the old radio that originality was not the best policy! .. now got a nice modern 3 core mains running straight into it.  Earth is firmly attached to the metal speaker grille ... just in case!

ICBM

ESchap said:

Decided with the old radio that originality was not the best policy! .. now got a nice modern 3 core mains running straight into it.  Earth is firmly attached to the metal speaker grille ... just in case!

You know this anyway, but - for anyone else reading - originality is never the best policy!

Safety

Reliability

Performance

Originality

...in that order, unless it's a museum piece that no-one will ever use.

I don't change original parts unnecessarily, but I never hesitate to if they compromise any of the more important factors.

ESchap

ICBM said:

ESchap said:

Decided with the old radio that originality was not the best policy! .. now got a nice modern 3 core mains running straight into it.  Earth is firmly attached to the metal speaker grille ... just in case!

You know this anyway, but - for anyone else reading - originality is never the best policy!

Safety

Reliability

Performance

Originality

...in that order, unless it's a museum piece that no-one will ever use.

I don't change original parts unnecessarily, but I never hesitate to if they compromise any of the more important factors.

I totally agree with you on this.  I keep looking at that Bulgin socket on my Plexi ...... and the mains wires now visible on the mains connector cable side ... not been using it recently, but may put an order in with TAD before I do.

ICBM

ESchap said:

I totally agree with you on this.  I keep looking at that Bulgin socket on my Plexi ...... and the mains wires now visible on the mains connector cable side ... not been using it recently, but may put an order in with TAD before I do.

I have some of those TAD sockets, unless you're putting an order in with them anyway.

I have persuaded the chap you got that one from that all amps he sells as working items should now have them fitted. (I think partly so he can sell the old cables separately to the US!)

ESchap

I'll be in touch @ICBM, thanks for letting me know.

Sessionman

It would be nice if musicians observed/read the fuse specs on their equipment!  Please, instead of sending stuff back under warranty because 'the fuse keeps blowing', read the specs!

Example, if it says T1F fuse... it means T1A... not F1A!  The latter will blow almost the first time you switch the appliance on.  Especially if the equipment has a 'Toroidal' mains transformer installed.  These exhibit a bigger turn on current (surge) than standard laminated types.

Believe it or not, this used to cost us loadza dosh every year in return carriage fees... when it was not our fault!

Sermon over! 

ICBM

The question would be why did the original T1A fuse blow, though… even if it was a mains spike or an incorrect load (I thought Sessionettes always had the extension speaker socket in series so that couldn't easily happen, but I could be wrong) it would still warrant (ha!) a factory check-over and bench test, really.

ecc83

Sessionman said:

It would be nice if musicians observed/read the fuse specs on their equipment!  Please, instead of sending stuff back under warranty because 'the fuse keeps blowing', read the specs!

Example, if it says T1F fuse... it means T1A... not F1A!  The latter will blow almost the first time you switch the appliance on.  Especially if the equipment has a 'Toroidal' mains transformer installed.  These exhibit a bigger turn on current (surge) than standard laminated types.

Believe it or not, this used to cost us loadza dosh every year in return carriage fees... when it was not our fault!

Sermon over! 

Heh! Fusing is more a black art than science! The balance between protection and nuisance blowing can be a fine one. 

As for punters fitting the wrong type? Every S1 200 I  saw where 88s had gone ape***t had blown the FAST 1A anode fuse and it had been replaced with a T type. Did not really matter since the main HT (T) fuse usually went as well plus the 3.15A mains and often, as I said earlier, the 13A in the plug. 

Time/dosh wasters? The biggest one I got was an A30 combo (wayzaton) shipped to us for a FRAYED HANDLE!!   The irony is you don't even have to take the back off the amp! Four screws is all it takes to swap a handle that would cost less than a fiver to send bloody airmail!

And heaven forfend any "shop person" should change even a pre amp valve!

Dave.