Color code for fusible resistors? - Page 1
Forum section: electronics / projects

author: metertech58761
author_rank: Frequent Contributor
timestamp: October 16, 2024, 01:04:41 am
content: I don't know if anyone has any time to answer my question, but here goes -There are some fuses with a bright green body that have a color code like a resistor; how do you read the rating from its markings?The one I have at hand has red / red / black bands. Is it 2.2A or 220mA?

author: Xena E
author_rank: Frequent Contributor
timestamp: October 16, 2024, 04:24:38 am
content: Usually a fusable resistor has itsresistancevalue and tolerance marked the same as a normal resistor. The last band is usually white solely to identify it as fusible.The power rating of the resistor vs the actual value is what is used to calculate when it is designed to open.Yours is 22Ω. More than that I can't help you with, you need to know the rating from the manufacturers data.E

author: MathWizard
author_rank: Super Contributor
timestamp: October 16, 2024, 06:01:00 am
content: On computer PSU's, I've seen pink bodied fuse-able resistors, the big ~1inch through-hole kind, I think they have an extra color band on them, but the normal bands still code the resistance, like 15mOhm was something with black, brown and green.

author: metertech58761
author_rank: Frequent Contributor
timestamp: October 17, 2024, 03:17:39 am
content: Quarter-watt, so I guess 100 milliamperes.

author: metertech58761
author_rank: Frequent Contributor
timestamp: October 17, 2024, 07:52:40 am
content: The thing is, 100 milliamps doesn't make sense.The main fuse is 10 amps fast blow.This fusible resistor lies in the main transmit B+ line, so 100 milliamps is absurdly low.

author: TimNJ
author_rank: Super Contributor
timestamp: October 18, 2024, 03:56:56 am
content: “B+ transmit line” of what? Show a photo? Is it an inductor?

author: metertech58761
author_rank: Frequent Contributor
timestamp: October 22, 2024, 02:00:59 am
content: Here's the schematic and picture of the board set.The part in question is F2 on Panel B, and in the picture, you can see most of it by the positive end of the large silver electrolytic at top.

author: metertech58761
author_rank: Frequent Contributor
timestamp: November 05, 2024, 01:32:25 pm
content: Found another picture - the fuse is on the corner, and a second one with the same markings is on the daughterboard.

author: bobxyz
author_rank: Contributor
timestamp: November 05, 2024, 03:57:09 pm
content: I don't think the color code for the extra band is standardized, but here's an example fromhttps://www.vishay.com/docs/28737/nfr25.pdf"MARKINGThe nominal resistance and tolerance are marked on theresistor using four colored bands in accordance withIEC 60062, marking codes for resistors and capacitors.For ease of recognition a fifth ring is added, which is violetfor type NFR25 and white for type NFR25H."

author: Kim Christensen
author_rank: Super Contributor
timestamp: November 05, 2024, 04:57:59 pm
content: Quote from: metertech58761 on October 17, 2024, 07:52:40 am100mA @ 170V is 17W input power which doesn't seem unreasonable for an amplifier with such limited heatsinking:

author: metertech58761
author_rank: Frequent Contributor
timestamp: November 07, 2024, 02:15:04 am
content: I guess that does make sense.There is a later version that uses a lower voltage for that transmit function (calling it +48V for now), and the single pair of output transistors uses strips of 1.5" x 1/2" x 1/8" sheet aluminum as heatsinks; that circuit has no fuses at all.So I'll consider this little mystery solved. Much appreciated.