5W resistor ?, marked 0.1ohm, 5W

[N_Cook]

I cracked the white outer ceramic block and instead of wire/strip around
a ceramic core, what looked exactly like a 2W metal oxide resistor,
complete with brown,black,silver bands .
Does wrapping a 2W resistor in fire-cement and preform ceramic hollow
block, make it 5W?

[Rheilly Phoull]

Sounds more like our overseas friends creative component marketing.

[ohg...@gmail.com]

On Tuesday, June 6, 2017 at 8:41:15 AM UTC-4, N_Cook wrote:

> Does wrapping a 2W resistor in fire-cement and preform ceramic hollow
> block, make it 5W?

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.

[N_Cook]

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

[N_Cook]

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

[Phil Allison]

N_Cook wrote:

--------------

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

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

http://www.mojotone.com/Metal-Oxide-2W-10-OHM-Resistor-10-image.jpg

https://3.imimg.com/data3/CO/AE/MY-8302870/wire-wound-resistor-250x250.jpg




..... Phil

[Phil Allison]

N_Cook wrote:

----------------

>
>
> Its in the speaker return path as a protector ,
>

** 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

[N_Cook]

On 06/06/2017 18:16, N_Cook wrote:
> I scraped back some of that typical dusty grey coating of the "MO" and
> it is actually wire wound

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

[olds...@tubes.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.

[Foxs Mercantile]

On 6/7/2017 1:38 PM, olds...@tubes.com wrote:
> You can buy those low resistant resistors on ebay, rated at
> 100 watts, for about $1 each.

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

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[Gareth Magennis]

wrote in message news:tehgjcll021bo3qjg...@4ax.com...

************************************************************



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%.


http://www.farnell.com/datasheets/1498243.pdf?_ga=2.189825763.930466988.1496871749-1771980843.1483642398



Gareth.

[Phil Allison]

Foxs Mercantile wrote:

---------------------

>
>
> 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.
>

** 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