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
T type fuses
Dec 03, 2013
6 Replies
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 "
** Doubt that is a "T" fuse at all.... Phil
"dave d*****ad "
** Would you please upgradee yours and put it to good use ASAP ? ** Blah, blah, blah - relevant to nothing.Massive logical fallacy.
** Meaningless, paranoiac advice.Begs the question.
.... Phil
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.
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
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