Metal Film or Carbon Film Resistors in Marcof PPA-1h ??

Ron AKA · 16th September 2011, 07:36 PM

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??

Rodeodave · 16th September 2011, 07:49 PM

5-band 1% carbon film resistors? I could be wrong, but I don't think they make 'em like that.

ticknpop · 16th September 2011, 08:16 PM

They are 1% , likey metal film

simon7000 · 16th September 2011, 08:20 PM

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.

john dozier · 16th September 2011, 08:31 PM

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

Ron AKA · 16th September 2011, 08:55 PM

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.

simon7000 · 16th September 2011, 09:02 PM

Quote:

Originally Posted by Ron AKA

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.

Ron AKA · 16th September 2011, 11:36 PM

Quote:

Originally Posted by simon7000

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

Steve Dunlap · 16th September 2011, 11:43 PM

Quote:

Originally Posted by simon7000

Change the loading resistor to a dale RN65 type. That will be an improvement.

I agree with this.

They used carbon film resistors.

mickeymoose · 17th September 2011, 12:09 AM

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

16th September 2011, 07:36 PM	#1
Ron AKA diyAudio Member Join Date: Aug 2011	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??

16th September 2011, 07:49 PM	#2
Rodeodave diyAudio Member Join Date: Dec 2004 Location: in the alps Blog Entries: 1	5-band 1% carbon film resistors? I could be wrong, but I don't think they make 'em like that. __________________ Gravity - Making the G since 13.7 billion B.C.

16th September 2011, 08:31 PM	#5
john dozier diyAudio Member Join Date: Dec 2010 Location: columbia sc	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 __________________ Evil looms. Cowboy up. Kill it. Get Paid.

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16th September 2011, 08:16 PM	#3
ticknpop diyAudio Member Join Date: May 2005 Location: toronto	They are 1% , likey metal film

16th September 2011, 08:20 PM	#4
simon7000 diyAudio Member Join Date: Nov 2008 Location: Oakmont PA	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.

16th September 2011, 08:55 PM	#6
Ron AKA diyAudio Member Join Date: Aug 2011	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.

17th September 2011, 12:09 AM	#10
mickeymoose diyAudio Member Join Date: Nov 2008	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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