Laney TI15-112 undersized HT fuse?

[trobbins]

It would appear to be an IEC compliant fuse is needed rather than a UL. In normal operation in that B+ feed location there is effectively no difference between a T (time delay) or F (fast), as the fuse is after the main filter capacitor. As Helmholtz indicates, an IEC spec fuse has to last 1hr at 150mA, so given the 120mA ammeter reading for cranked it would suggest either a UL fuse was being used (as that has no spec for blowing if the current exceeds 100mA except to last 5 secs for 200mA), or that something else was abnormal.

One abnormal issue could be a poor speaker connection - eg. the socket contacts are bad, or someone was trying to connect an external speaker - if the output was open-circuit, and someone was playing hard with vol up then the output tubes would be forced in to gross conduction (ie. worse than cranked).

[tdlunsfo]

I did some testing a while back to determine the characteristics of fuses and found that many cheap fuses did not behave predictably and did not comply with the specification.

All the fuses in the amp are of the same type and manufacturer, so I am inclined to belief they are original.

[tdlunsfo]

It would appear to be an IEC compliant fuse is needed rather than a UL.

I have to admit, I learned something new here as I was completely unaware of any UL vs. IEC differences. I'll have to research this further.

[pdf64]

It ought to be more of an issue than it seems to be?
I’ve always fitted lower value fuses to Fenders and other USA amps than specified, but then multi voltage amps only ever used to specify the fuse value appropriate for 117V operation, which is far higher than appropriate for 240V.
Actually, that also applies the old AC30 and their 3A mains fuse spec.
Halving the spec value was usually a step too far though, which is a bit confusing.

[tdlunsfo]

https://www.optifuse.com/blog/t090821.php

[Helmholtz]

How about lowering the bias?

Lowering idle currents won't help.

Acc. to EL84 charts, total current draw at full power is exactly the same for 7.5mA (class B) or 36mA (class AB) at idle.

[Mick Bailey]

All the fuses in the amp are of the same type and manufacturer, so I am inclined to belief they are original.

is there any other identification on the fuse end caps to suggest which standard the fuse meets, or manufacturer? I'm inclined to think it's a Chinese amp with Chinese fuses. Hmmm..... It shouldn't be an issue, but worth checking.

[tdlunsfo]

Found a LF symbol which appears to be the marking for Littelfuse. There are an additional 6 symbols on the other end for international approval markings for Germany (VDE), Sweden (Circle S), Canada (CSA), China (CCC), USA (UR), then an ICC (import commodity clearance?).
Amp says designed in the UK and made in China.

[Kevina]

Go to the website of your preferred fuse supplier, and key in T100mA.

Download the datasheets for each of the fuses stocked, and look carefully at the graph plotting the I/t characteristics. There is quite a wide variance.

We once had a particularly troublesome unit. I did as above, and chose a particular fuse which had a much superior characteristic to its competitors. On testing the fuse under EN60065 fault condition limits, the fuse still blew in the same time as the original test, but we never had another "nuisance blow" fuse problem reported.

[Jon Snell]

Go to the website of your preferred fuse supplier, and key in T100mA.

Download the datasheets for each of the fuses stocked, and look carefully at the graph plotting the I/t characteristics. There is quite a wide variance.

We once had a particularly troublesome unit. I did as above, and chose a particular fuse which had a much superior characteristic to its competitors. On testing the fuse under EN60065 fault condition limits, the fuse still blew in the same time as the original test, but we never had another "nuisance blow" fuse problem reported.

Agreed. Use the original specification fuse and there will be no issues.
Intermittently blowing fuses is usually down to one of two things;
1/ A fault.
2/ Incorrect fuse fitted, which may even mean, unknown supplier; Fleabay, Amazon etc.