Metal Film or Carbon Film Resistors in Marcof PPA-1h ?? - diyAudio
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Old 16th September 2011, 08:36 PM   #1
Ron AKA is offline Ron AKA  Canada
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Default Metal Film or Carbon Film Resistors in Marcof PPA-1h ??

Here is a picture of some resistors on this 1979 vintage moving coil head amp from Marcof. Do you think these are carbon film or metal film design? Since this is a high gain (34 dB), very low signal device, I was thinking it could benefit from a lower noise resistor. Noise here is further amplified by the phono section amp, then the pre-amp, and finally the power amp. Metal foil would seem to be the best but is not available in correct values, and metal film would appear to be the next best choice.

I'm thinking the beige body color and the vintage would suggest carbon film??

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Old 16th September 2011, 08:49 PM   #2
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5-band 1% carbon film resistors? I could be wrong, but I don't think they make 'em like that.
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Old 16th September 2011, 09:16 PM   #3
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They are 1% , likey metal film
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Old 16th September 2011, 09:20 PM   #4
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The double width last band is the give away. Blue body color is usually meant to mean flame proof. As modern metal film resistors do not contain carbon they are flame proof. Double width tolerance band means metal.
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Old 16th September 2011, 09:31 PM   #5
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Texas Components will make Vishay foil resistors in any value and tolerance that you need. Price may be higher than you are willing to pay however. Regards
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Old 16th September 2011, 09:55 PM   #6
Ron AKA is offline Ron AKA  Canada
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Thanks for the quick responses. On a check it appears 1% carbon film resistors are now about as common as hen's teeth. Anyone know if it was the same 30 years ago? If so along with the other clues it would seem virtually 100% certain these are metal film. Thought there might have been a cheap upgrade to reduce noise, but it appears not.
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Old 16th September 2011, 10:02 PM   #7
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Quote:
Originally Posted by Ron AKA View Post
Thanks for the quick responses. On a check it appears 1% carbon film resistors are now about as common as hen's teeth. Anyone know if it was the same 30 years ago? If so along with the other clues it would seem virtually 100% certain these are metal film. Thought there might have been a cheap upgrade to reduce noise, but it appears not.
Change the loading resistor to a dale RN65 type. That will be an improvement.
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Old 17th September 2011, 12:36 AM   #8
Ron AKA is offline Ron AKA  Canada
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Originally Posted by simon7000 View Post
Change the loading resistor to a dale RN65 type. That will be an improvement.
By the loading resistor do you mean the loading resistor for the amp (R7 in the circuit drawing at the link below)? Or the loading resistor for the moving coil (R1)?

Marcof PPA-1h Circuit Drawing

Yes, there appears to be differences in the types of metal films. See the figures near the end of the article below. However, finding the good ones in small quantities seems to be another matter. Sources for the RN65? Is that just a military designation for the Dale CMF?

Resistor Current Noise Measurements
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Old 17th September 2011, 12:43 AM   #9
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Quote:
Originally Posted by simon7000 View Post
Change the loading resistor to a dale RN65 type. That will be an improvement.
I agree with this.

They used carbon film resistors.
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Old 17th September 2011, 01:09 AM   #10
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Why would anyone do carbon-film in 1%? Take out one R and get a metal-film of the same resistance. Attach wires, measure at room temp. Put in oven to about 100 Deg.C, measure again and compare resistance. The mf should have less than 10% drift of the cf. E
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