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Resistor wattage, any way to find out?

G

GytisB

Member
Hi! I was a bit unlucky and broke a resistor in the volume section of the amp (relay based, with the clicks/ticks every time you adjust the volume). Finding out resistance is not a big deal, since it's marked on the PCB, but the lack of service manual makes it hard to predict the correct wattage. Since it's job is to adjust the volume, I believe I don't really need a very powerful one? Something like a 1/2 watt metal film should be sufficient? or should I go for 1 watt? Do I need to go for the "non flammable" or any metal film is fine? Thank you in advance!
 

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Probably 1/2 watt. But some metal films rated for 1/2 watt are the size of 1/4 watt and I've run across 1 watt resistors the size of 1/2 watt. They do look like 1/2 watt though. Metal film is fine. I would just use a 1/2 watt.
 
Lavane said:
Probably 1/2 watt. But some metal films rated for 1/2 watt are the size of 1/4 watt and I've run across 1 watt resistors the size of 1/2 watt. They do look like 1/2 watt. If it is a 1/2 watt, 1 watt will work just as well as a 1/2 watt. It will just allow a little more current.
Click to expand...

Alright! Makes sense! Will go for stronger, 1 watt ones and be safe! Thank you!
 
I recently came across this chart when I was trying to figure out the wattage rating of some resistors I already had. Apparently you can determine power capacity by size, which makes a lot more sense to me than just guessing.

https://www.electricalengineering.xyz/sheet/resistor-power-rating-chart/

I think this must only apply to modern resistors; the 1 watt carbon resistors in my circa 1960 Scott amp are much larger than what shows on this chart.
 
petehall347 said:
probably 1/4 watt .
Click to expand...
Possible. 1/2 watt should work though. I've been getting more 1/2 watt resistors that look like 1/4 watt resistors in my orders lately. At first I didn't trust them. But haven't had any issues with them. Some of the 1 watt have been the size of 1/2 watt resistors too.
 
looks like they are for audio signal so wont need to be high wattage . yes of course 1/2 watt will work equally as well . the tolerance needs to be right .
 
Ran into "geometry" where refitting a board for an older amplifier section.. the dated components were huge, resistors, caps, and transistors. Fast forward the spec associated replacements, smaller and seemingly of lightweight materials. In some cases, it actually made mating the leads to the panels a real challenge, too much real estate available :eek:
 
Ooo! I think that measuring the actual size and going from there is a very good idea:idea::thumbsup: I appreciate all the answers, great info!
 
problem is there are big and small 1/2 watt parts. I've bought 1/2w parts that are the dimensions of 1/4w parts, sometimes by accident, sometimes because it was all that was available.

I'd probably match it up on dimensions and value, and if there are multiple power levels, go for the higher one.

or just measure voltage drop across it to verify one of the 1/2w parts I have on hand will handle the abuse and roll with it.
 
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