Flex resistors ? - Printable Version

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Flex resistors ? - Eric - 06-26-2013

I have a Stromberg Carlson 240L but this question is pretty generic. It has a Flexible Resistor R-20 rated at 200 ohms my questions are ...

1 Why were they used instead of standard resistors? I'm guessing they cost more?

2 How can I determine the Wattage? Any rule of thumb?

I have 2w and a 5w I can use plenty of room so I was planning to use the 5w
Eric

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RE: Flex resistors ? - Mondial - 06-26-2013

The flex resistors are actually wirewound resistors made from resistance wire wrapped around a flexible asbestos or glass fiber core.They were typically used for stable low resistance values which were difficult to get in carbon.

The wattage rating will depend on physical size. A one or two inch long resistor might be rated at a watt or so. Unless the flex resistor is extremely long or large, the 5 watt would seem to be a safe replacement.

Is the existing resistor open? They are usually fairly reliable and typically hold tolerance well.

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RE: Flex resistors ? - Eric - 06-26-2013

It was in pieces, it was about 3" long I know that they are wire wound just wonder why use them?
Now I have another ?
I have several dog bones that measure 3" the chart I have shows a 2w being 1 1/4" so if I need to replace I would also need around a 5w?
The parts bulletin refers to them as a type "F"

Eric

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RE: Flex resistors ? - codefox1 - 06-27-2013

So long as you can sub a good modern carbon or wirewond of the same value and wattage for a failed component, good. Try to find out why original failed first. If analysis shows part of a voltage divider, then the hunt is on.........

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RE: Flex resistors ? - Arran - 06-28-2013

Flexible resistors seem to have been somewhat of a fad in the mid to late 1930s, I think that the reason they were used was so they could install a higher wattage resistor in a tight space. I've often found them installed between pins under a tube socket where a rigid wire wound from that day would not fit. They also have a nasty habit of cooking themselves to death, the casing was mostly made out of "spaghetti" type tubing like they used to use around capacitor leads. Eventually through heat and age the tubing breaks down and starts falling apart. I would replace the flexible resistor with a modern wire wound or metal oxide resistor, they are much more compact then they used to be.
Regards
Arran

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RE: Flex resistors ? - Eric - 06-28-2013

Thanks for the info,
Eric

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