5W resistor ?, marked 0.1ohm, 5W

Sounds more like our overseas friends creative component marketing.

They're not rated in amps, but watts. Soooooooooo..... If you can sink off enough heat you can raise the wattage rating of a resistor. What I don't know is whether you can get a two watt resistor to safely dissipate 5W with the package you describe.

Sony used a lot of 0.1 ohm ceramic encased resistors as fuses, but these were encased for fire retardence and eliminated the loud pop/snap a regular 0.1 resistor made when the mosfets after them shorted.

If there's another one like it in the circuit you can experiment.

Its in the speaker return path as a protector , annoyingly its not o/c but PbF tinpest? build up around its wire was causing the o/c. In a Crate Flexwave 120/212 of 2008, with (tick) N222 "compliance" mark = PbF ? the solder does not react as PbF when admixing with SnPb . I cracked the casing using too sharp and edge screwdriver , to force the issue, to prove solder joint failure, levering against the pcb. Same ohm+zigzag logo as the other apparent 5W 0.47R emitter resistors

I scraped back some of that typical dusty grey coating of the "MO" and it is actually wire wound

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** The first pic shows a MO resistor, but there are WW examples that look near identical - as in the second pic.

..... Phil

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** No way it is for protection.

The 0.1ohm is part of a positive feedback network to INCREASE the output impedance of the power amp.

The low output impedance (or high damping factor) of a SS power amp is not desirable in a guitar amp - so this trick fixes it.

Makes the impedance more like 8ohms - so a DF of 1.

..... Phil

A genuine maker and seller of 0.1R, 2W w/w resitors would wind them with nichrome wire that could carry 4.5 amp current continuously but a genuine 5W version , he would use wire that would have to carry 7.1 amp continuously

You can buy those low resistant resistors on ebay, rated at 100 watts, for about $1 each. (from China). I bought a pair of 8 ohm ones, to use for speaker load resistors, when I am testing power amps. They have an aluminum housing with heat sink fins. It took about 3 weeks to get them in the mail, but I was not in any hurry.

I know the OP said they are for speakers, but I do question their purpose. Throw one of them 100W ones in there and it will last forever.

Which is ABSOLUTELY NOT what Nigel needs. He's replacing a 5 watt 0.1 ohm resistor in an amplifier. The problem is that the original had 2 watt resistors inside a

5 watt body. I.e., cheap counterfeits.

Please try to keep up.

--
Jeff-1.0 
wa6fwi 
http://www.foxsmercantile.com

You can buy those low resistant resistors on ebay, rated at 100 watts, for about $1 each. (from China). I bought a pair of 8 ohm ones, to use for speaker load resistors, when I am testing power amps. They have an aluminum housing with heat sink fins. It took about 3 weeks to get them in the mail, but I was not in any hurry.

I know the OP said they are for speakers, but I do question their purpose. Throw one of them 100W ones in there and it will last forever.

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If you are talking about this type of resistor, they are only rated at the stated Watts when mounted on a suitable heatsink.

If they are a dollar each from China, then you should probably derate them a further 75%.

Gareth.

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** They're not counterfeits.

Regular cement WW types have the same construction, a small ceramic tube with resistance wire wound on buried in cement and encased in a hard ceramic box.

The increased surface area provides the extra dissipation.

..... Phil