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carbon VS metal, resistors

bobbyonions

bobbyonions

AK Member
Hi all. I'm not trying to start any wars here, but I'm having a rough time deciding on what kind of resistors to put in my late 50's pilot SA-160 stereo amplifier (PP el34).
I'm looking for some input from folks who have a lot of experience restoring and rebuilding this era tube gear. I've read everything I can find online pertaining to this, and I'm just as confused as ever. This thread may generate many conflictiong opinions, but I'm hoping it will educate me a little and knock me off the fence one way or the other. Thanks, Dave.
 
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If you want to preserve the original sound of the amp as much as possible I would think replacing any resistors with their current equivalent would be the way to go. Carbon film will likely be a better choice than carbon comp, just make sure they are rated for a high enough voltage and equal or slightly higher wattage rating.
 
I use metal film resistors in all positions when restoring old tube gear, excepting high-power wire-wound types. There might be a *slight* loss of authenticity in sonic signature, but I'm sure it's small, and I'll be darned if I'm going to put myself through all of that misery to install components with such rotten provenance.
 
Thanks, there's two votes for carbon films right off the bat. That's kind of the way I'm leaning based on what I've read already.
The one thing keeps me considering carbon comps is the idea that the designers of this amp designed around carbon comps. If they tailored the circuit based on what they were hearing, than I can see a fair argument for sticking with cc if you can put up with the possible noise they introduce.
 
bobbyonions said:
Thanks, there's two votes for carbon films right off the bat. That's kind of the way I'm leaning based on what I've read already.
The one thing keeps me considering carbon comps is the idea that the designers of this amp designed around carbon comps. If they tailored the circuit based on what they were hearing, than I can see a fair argument for sticking with cc if you can put up with the possible noise they introduce.
Click to expand...

Not really, carbon comp resistors were pretty much the most commonly available resistors back then. Of course they also had wire wound resistors, but carbon film, metal film, tantalum film and other "exotic" resistors either didn't exist back then or were astronomical in price.
 
Carbon film on signal and cathodes, metal on plate voltages and power supply in general. carbon comps, drift and are noisy. Just because something is old school, don't mean it's better.:D

If you don't mind spending a few extra dead presidents, Parts Connexion has some really sweet Rs for like signal in spots and such.:music:
 
I found in certain circuits too much metal can cause an edginess that is fatiguing. I like to use them because the matching is so quick and easy, but don't use to many right in the amp circuit.
 
Metal film resistors on plates and power supplies are ok as long as the maximum voltage rating of them aren't exceeded. And I don't recommend them for grid stoppers either.
 
For Me,

I don't use metal based resistors on anything that's direct signal path related, an that
includes the plate load, I tend to stick to carbon film in most every position an sprinkle
in a few metal film, carbon comp and wire-wound where larger dissipation's are needed.

From my perspective carbon film is the resistor that's in the middle and imparts less of
anything on the signal, there good all around resistors, metal films tend to be the quiet
ones of the bunch but to me can get edgy in the wrong circuit/spot, carbon comp can
be noisy and impart an "vintage" tone into the mix that when to many are used is a bit
to much for my taste.
 
Are modern carbon comps any better quality than older carbon comps, ie less noisy/more stable? I've noticed there are several manufacturers available these days including ohmite. If they are no better than carbon film or metal film, and they certainly are not any less expensive, why are they still being made?
 
I can't say for sure if new ones today are better then the older ones, if I had
to guess I'd say, yah I'd believe new tech could make a better version, as to
why there still made is because of vintage pieces an the tone many are after.
(many vintage amp, plus guitar people swear by there carbon comp resistors)
(carbon comp tend to be high voltage tolerant and are non inductive as well)

I use a few carbon comp in new builds I do for a sprinkle of tone here n there
sometimes when I feel the need/want on a given setup/piece.
(another good use for them is grid stoppers)
 
Thanks everyone. I feel much more confident about how to approach this now. I know I'm in good hands here. I've been studying schematics, and comparing it to my gear for a few years. Within the last year it finally started making a little sense (I can at least identify and visually trace wiring against the schem, change caps, resistors, etc.). Just being able to confidently drain caps so I knew I wouldn't fry myself was a hurdle that took a while to cross.
I'm in a fun place right now as far a learning. There are a lot of dots that are starting to connect, bits and pieces of seemingly unrelated information are gelling into larger chunks of understanding. It's really encouraging.
I have a healthy stock of carbon films that I think I will use predominately throughout for now. There seems to be an overwhelming consensus supporting those in general, except for a few key spots where people tend to differ a little on their flavor. I'm still a little fuzzy on where those critical spots are in this amp, so CFilm for now seems fair and down the road I can play with some enhancements as I learn more.
Thanks for all your input. I have read tons of posts by most of you and have always been impressed with your thorough knowledge, skill, generosity, and no BS approach to what you do.
Special thanks to Jim (ab0ze) for going out of his way to help me with this over on my restore thread. I trying to think of something good to drop in the mail for you.
Dave
 
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Kegger said:
1:For Me,

I don't use metal based resistors on anything that's direct signal path related, an that
includes the plate load, I tend to stick to carbon film in most every position an sprinkle
in a few metal film, carbon comp and wire-wound where larger dissipation's are needed.

From my perspective carbon film is the resistor that's in the middle and imparts less of
anything on the signal, there good all around resistors, metal films tend to be the quiet
ones of the bunch but to me can get edgy in the wrong circuit/spot, carbon comp can
be noisy and impart an "vintage" tone into the mix that when to many are used is a bit
to much for my taste.

2:For Me,

I don't use metal based resistors on anything that's direct signal path related, an that
includes the plate load, I tend to stick to carbon film in most every position an sprinkle
in a few metal film, carbon comp and wire-wound where larger dissipation's are needed.

From my perspective carbon film is the resistor that's in the middle and imparts less of
anything on the signal, there good all around resistors, metal films tend to be the quiet
ones of the bunch but to me can get edgy in the wrong circuit/spot, carbon comp can
be noisy and impart an "vintage" tone into the mix that when to many are used is a bit
to much for my taste.
Click to expand...
These posts should be a sticky for everyone to read.
 
While I have the attention of some gurus;

After I finish with the pilot sa-260, I want to give my pilot sp-210 the spa treatment too. Are carbon films generally going to be the way to go in the pre as well? Thanks.
 
That's what I would use, with the only exception being where an extremely accurate (value wise) resistor would be called for that wasn't directly in the signal path. Just my opinion and YMMV.
 
bobbyonions said:
While I have the attention of some gurus;

After I finish with the pilot sa-260, I want to give my pilot sp-210 the spa treatment too. Are carbon films generally going to be the way to go in the pre as well? Thanks.
Click to expand...

Yes, carbon film is good, the only place metal is good to me is in RIAA EQ circuits (1%ers).
 
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