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Author Topic: Are metal film resistors the same as flame proof resistors  (Read 4135 times)
KA5ROW
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« on: May 04, 2015, 07:07:26 AM »

Are metal film resistors the same as flame proof resistors sold today? I read on the Internet and it said the metal film was the common resistor used today. I had a resistor get very hot when I put a bad 12BY7 tube in a Kenwood TS-830. The Kenwood service manual made it specific to use a metal film resistor. Maybe in 1983 metal film was special.
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N3QE
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« Reply #1 on: May 04, 2015, 08:27:21 AM »

Are metal film resistors the same as flame proof resistors sold today? I read on the Internet and it said the metal film was the common resistor used today. I had a resistor get very hot when I put a bad 12BY7 tube in a Kenwood TS-830. The Kenwood service manual made it specific to use a metal film resistor. Maybe in 1983 metal film was special.

Most flame proof resistors are metal film. But not all metal film resistors are flameproof, only a certain subset are.

Your typical metal film resistor can get to be glowing red hot, have burned off all their color coding, and still not have changed their resistance. But that's still not the same as getting the official "flameproof" designation.

Fusible resistors are yet another category that you didn't raise (most of the fusible resistors I've seen are sand).

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KD0REQ
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« Reply #2 on: May 13, 2015, 06:37:07 PM »

in 1983, those "safety flameproof" resistors in 2-packs from RCA Parts started at a buck a resistor for quarter-watters.
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W5RKL
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« Reply #3 on: May 18, 2015, 01:28:36 PM »

Are metal film resistors the same as flame proof resistors sold today? I read on the Internet and it said the metal film was the common resistor used today. I had a resistor get very hot when I put a bad 12BY7 tube in a Kenwood TS-830. The Kenwood service manual made it specific to use a metal film resistor. Maybe in 1983 metal film was special.

You have to read the data sheet for the specific type of film resistor. The data sheet will state whether the resistor is made of "Flame retardant epoxy coating" material. The following Mouser part number is for a 10K 1/4 watt metal film resistor.

71-CMF5510K000BEEB

The data sheet for the metal film resistor can be found at the following link:

http://www.mouser.com/ds/2/427/cmfind-239942.pdf

Also, not all metal film resistor have the same DC voltage ratings. For example, the 1/4 watt resistor with the Global Model identifier CMF50 in the part number has a maximum DC voltage rating of 200VDC. The "CMF55" 1/2 watt model states a maximum DC voltage rating of 250VDC. "CMF60", 1 watt resistor has a maximum DC voltage rating of 500VDC. You have to read the data sheet to ensure you are using the proper resistor.

73
Mike W5RKL
« Last Edit: May 18, 2015, 01:42:38 PM by W5RKL » Logged
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