I've always wondered about the T type fuses with seemingly tight Quick
type but diagonal fuse-wire and a blob in the middle, compared to the
more obviously forgiving ones with a spiral wind over a core or a spring
like part of the wire.
Laney VC30 valve amp of 1996 with a blown HT fuse. I cannot confirm with
the owner until tomorow whether it failed at switch on and have so far
not tested the valves. Barely noticable small white patch on the glass
barrel of the fuse, so soft blown. At leat 2 years of useage most days
and all valves no fading of the markings . 4 x EL84 on the HT. The
manual specifies T315mA spiral wound but the failed one is the straight
form unless there was a tiny springy bit in the middle , evapoated,
rather than the usual springy bit at one end. Remnant wire is still
diagonal , just 2mm missing in the middle.
So replace with a T315mA spiral one and not go up to 500mA? assuming
the valves test ok

On 12/03/2013 08:18 AM, N_Cook wrote:
I've always wondered about the T type fuses with seemingly tight Quick
type but diagonal fuse-wire and a blob in the middle, compared to the
more obviously forgiving ones with a spiral wind over a core or a spring
like part of the wire.
Laney VC30 valve amp of 1996 with a blown HT fuse. I cannot confirm with
the owner until tomorow whether it failed at switch on and have so far
not tested the valves. Barely noticable small white patch on the glass
barrel of the fuse, so soft blown. At leat 2 years of useage most days
and all valves no fading of the markings . 4 x EL84 on the HT. The
manual specifies T315mA spiral wound but the failed one is the straight
form unless there was a tiny springy bit in the middle , evapoated,
rather than the usual springy bit at one end. Remnant wire is still
diagonal , just 2mm missing in the middle.
So replace with a T315mA spiral one and not go up to 500mA? assuming
the valves test ok

I don't recommend "upgrading" any suicide device, whether it be a fuse
or a 1/4W resistor or a seemingly tiny diode. I have seen a 25KW RF amp
destroyed because an "engineer" thought 18g stranded at the bottom of
the rectifier stacks (aka B-) couldn't handle 4 Amps and replaced it
with some 12g hookup wire, subsequently nuking the tube and socket when
the DC block capacitor shorted or arced. Be very careful and beef things
up only if you are certain you are not doing further harm.

"Nutcase Kook "

Remnant wire is still diagonal, just 2mm missing in the middle.


** Doubt that is a "T" fuse at all.



.... Phil

"dave dickhead "

I don't recommend "upgrading" any suicide device,


** Would you please upgradee yours and put it to good use ASAP ?


I have seen a 25KW RF amp destroyed ...

** Blah, blah, blah - relevant to nothing.

Massive logical fallacy.


Be very careful and beef things up only if you are certain you are not
doing further harm.

** Meaningless, paranoiac advice.

Begs the question.



..... Phil

On 03/12/2013 16:18, N_Cook wrote:
I've always wondered about the T type fuses with seemingly tight Quick
type but diagonal fuse-wire and a blob in the middle, compared to the
more obviously forgiving ones with a spiral wind over a core or a spring
like part of the wire.
Laney VC30 valve amp of 1996 with a blown HT fuse. I cannot confirm with
the owner until tomorow whether it failed at switch on and have so far
not tested the valves. Barely noticable small white patch on the glass
barrel of the fuse, so soft blown. At leat 2 years of useage most days
and all valves no fading of the markings . 4 x EL84 on the HT. The
manual specifies T315mA spiral wound but the failed one is the straight
form unless there was a tiny springy bit in the middle , evapoated,
rather than the usual springy bit at one end. Remnant wire is still
diagonal , just 2mm missing in the middle.
So replace with a T315mA spiral one and not go up to 500mA? assuming
the valves test ok

I assume 250V rating only comes into play after a fuse has blown, ie
only 2mm or so fused gap . Buss make , and a load of compliance stamps
so I assume nothing wrong with the fuse other than its non-spiral
construction.

On 12/03/2013 06:04 PM, Phil Allison wrote:
"dave dickhead"


I have seen a 25KW RF amp destroyed ...
** Blah, blah, blah - relevant to nothing.

Massive logical fallacy.

.... Phil

Fusible links are a "Massive logical fallacy"? wtf?

Spiral wound T 315mA went back in there
One of those balance of probabilities fault deduction scenarios. There
was a bust valve but as zero current for zero bias probably failed spot
weld and failed months ago unnoticed as only used at low level.
Bad Hi socket meaning bad Lo input also, due to the cross-coupling
giving cracks and bangs. But also a bad spade at the speakers so
probably interpreted as the input problem and repeated moderate back-emf
surges straining the HT fuse that eventually gave up the ghost at a
normal switch on surge