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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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16th Sep 2021, 3:32 pm | #1 |
Hexode
Join Date: Feb 2011
Location: Newcastle upon Tyne, Tyne and Wear, UK.
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What is the resistor wattage of these examples
The brown one is 19mm body length, I think is 1 watt maybe 2watt
The white ones are 30mm body length maybe 2watt |
16th Sep 2021, 3:44 pm | #2 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
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Re: What is the resistor wattage of these examples
1st photo 1 Watt, 2nd photo 2 Watts a piece I would say.
Lawrence. |
16th Sep 2021, 4:44 pm | #3 |
Dekatron
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Location: Near Swindon, North Wiltshire, UK.
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Re: What is the resistor wattage of these examples
The first one could be an Allen Bradley hot moulded carbon (composition) or a Radiospares 2 Watt carbon composition type.
The second is an Erie ceramic cased carbon composition type - around 2Watts. |
16th Sep 2021, 5:08 pm | #4 |
Nonode
Join Date: Aug 2015
Location: Cambridge, Cambs. UK.
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Re: What is the resistor wattage of these examples
Resistor wattage rating is a rather interesting topic. How come that today’s resistors can be so tiny compared with those of 60 years ago?
What design factors determine the wattage rating? Thinking aloud….. Larger surface area clearly increases rate of thermal dissipation by convection, so it makes sense that higher power devices are larger. Thermal resistance between resistor element and external surface will vary. The old ‘dogbone’ resistors only had a layer of paint, but the later Erie tubulars had an outer ceramic shell which presumably increased thermal resistance. What of today’s carbon film and metal film resistors? I guess we’re back to just a layer of paint between the resistive element and free air. So are modern film resistors more tolerant of higher temperature operation than their vintage equivalents? Their smaller size suggests that they are. Martin
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16th Sep 2021, 5:27 pm | #5 |
Octode
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Location: Knutsford, Cheshire, UK.
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Re: What is the resistor wattage of these examples
I agree 1W for the first resistor on the left, and 2W for the Erie on the right.
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16th Sep 2021, 7:46 pm | #6 |
Dekatron
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Location: Colchester, Essex, UK.
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Re: What is the resistor wattage of these examples
Interesting that my Erie Hi-stab (30mm long) 1% resistors are labelled on the box as 1w- presumably de-rated to ensure they maintain their 1% performance.
Dave |
16th Sep 2021, 8:54 pm | #7 | ||
Rest in Peace
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Re: What is the resistor wattage of these examples
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16th Sep 2021, 11:35 pm | #8 |
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Re: What is the resistor wattage of these examples
I remember even in the 60's that Philips rated their carbon films two ways.
1 watt @ 100 C and 1/2 watt @ 70 degrees. Moulded carbon drift without heat, horrible noise makers. IRC made VERY small resistors in the 60's too, renowned for the end caps breaking off. They were only about 6mm long and about 1 1/2 mm long and rated at 1/2 watt. I also remember many imprints in my finger tips from the temperature they ran at. They were made on ceramic formers. As to the origional question, 1 watt and 2 watts as most of us have mentioned. Joe |
19th Sep 2021, 7:09 pm | #9 |
Hexode
Join Date: Feb 2011
Location: Newcastle upon Tyne, Tyne and Wear, UK.
Posts: 280
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Re: What is the resistor wattage of these examples
I have just bought some quarter watt 5% Allen Bradley NOS carbon comp, two thirds of them were way out, between 11% and 20% - dissapointing
They are tiny in size compared to the original ones also. |
19th Sep 2021, 7:27 pm | #10 |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
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Re: What is the resistor wattage of these examples
I understood that the main difference with modern resistors was that they are rated to withstand a certain power dissipation as long as you can find a way of keeping their surface temperature within the specified limit. Back in the day the manufacturers took that responsibility for you. They rated their components to survive at the specified power as long as they were in something close to 'free air' which wasn't unduly hot. These days keeping the temperature down is your problem, not theirs.
Cheers, GJ
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