Resistor Types

[AussieTim]

This question has probably been asked a million times but through trawling through pages and pages of posts I am non the wiser.
The build I am following (Trinity SIII) specifies all carbon comp resistors with a couple of exceptions
Every article that I have read says carbon comp is noisy, So the question is why use them?
I know that some people will say "that's because that's what the original had" to which I would reply that my dads old car originally had 1970,s tyres but today's tyres are so much better that you would not even consider sourcing the original type.
So is it the same with resistor types? Or is there another reason for using carbon comp I have read they withstand pulses well is this important? Or is it just nostalgic ****?
We all want to build great sounding amps but as we all know some people are not selling a bunch of components that anyone can buy at an electrical retailer they are selling MAGIC and claims of genuine components and how they you will effect your sound etc run rife. How many of these kits have purchased all their stuff from Mouser or Digikey and resold the same components at greatly marked up prices calling them special?
So the question remains what do we stay "vintage" with and what do we use a better modern component for
Thank you
Tim

[JMPGuitars]

So the question remains what do we stay "vintage" with and what do we use a better modern component for
Thank you
Tim

Take a look at my 36 watt build:
galleries/displayimage.php?album=lastup ... play_media

And this EF86 Lite:
galleries/displayimage.php?album=5&pid= ... play_media

There's only one spot I use carbon comp, I was once told it's the only spot that actually benefits from them. Whether or not it actually does, or actually sounds different, well, who knows. I generally stick to carbon film, and I've never really noticed a significant difference regardless of what I use in that spot.

Obviously there are those few other positions that require higher wattage, so I'll use WW, MF, or MO resistors depending on what I have or need.

Thanks,
Josh

[geoff 1965]

yeah i've looked into this myself and carbon comps claim to have a softer distortion so could make a difference using them for plate resistors i.e. phase inverter etc.
but in areas where the signal level is low like input,grid & cathode they can cause noise so i can't see the benefit of using them here.plus you have stability and tolerance to consider,i tried some allen bradley comps to be "authentic" but the tolerances were bad, 20% or more out.

[crgfrench]

Besides Thanksgiving, the only time I use my oven is for baking the Allen Bradleys, and it makes the whole house smell fantastic. So there's that...

[crgfrench]

There's only one spot I use carbon comp, I was once told it's the only spot that actually benefits from them. Whether or not it actually does, or actually sounds different, well, who knows. I generally stick to carbon film, and I've never really noticed a significant difference regardless of what I use in that spot.

I don't see why tone would benefit from CCs at the PI plate load resistors. It's not even in the signal chain.

Metropoulos has optional CCs at:

1) input grid leaks
2) input grid stoppers
3) preamp tube cathodes (not PI though)
4) volume pot wipers
5) TMB stack
6) NFB line

He does not have them anywhere else: nowhere in the PI section, nowhere in the DC filter and nowhere in the B+ line, including none of the plate load resistors.

[JMPGuitars]

I don't see why tone would benefit from CCs at the PI plate load resistors. It's not even in the signal chain.

Metropoulos has optional CCs at:

1) input grid leaks
2) input grid stoppers
3) preamp tube cathodes (not PI though)
4) volume pot wipers
5) TMB stack
6) NFB line

He does not have them anywhere else: nowhere in the PI section, nowhere in the DC filter and nowhere in the B+ line, including none of the plate load resistors.

what geoff said above, and then read this full article: http://www.geofex.com/article_folders/c ... oncomp.htm

Here's the most directly relevant part:
"The place to use CC's is where there's big signal - plate resistors, and ideally the stage just before the phase inverter. The phase inverter would otherwise be ideal, with plate resistors carrying the highest signal voltage in the amp, but phase inverters are often enclosed in a feedback loop. The feedback minimizes the distortion the resistor generates." - R.G. Keen

It was Graydon or Zaphod_Phil that originally told me about that. Essentially everything you listed from Metro is b.s. hype. Especially the NFB line that would counter the CC resistors. Since there is no NFB loop in these amps, where I use them at the PI plates is essentially the only place worth bothering...if you bother.

Thanks,
Josh

PS. "Old technologies never die - even if they should." - Kevin O'Conor (speaking about Carbon Comp resistors)

[crgfrench]

The audio signal does not pass through plate load resistors.

[JMPGuitars]

The audio signal does not pass through plate load resistors.

Does audio signal pass through plates? Do plate resistors affect the sound the tube produces?

Did you read the article? If there's no benefit to them being in other spots, and only added noise and potential problems, why would you use them? This isn't something R.G. made up. It's science, it's measurable, and it's repeatable.

[crgfrench]

I dont use them. I agree with Geoff they just add noise. I just dont see how they would benefit anything in the PI plate load resistor spot, which agrees with your own observation that you cant tell a sonic difference either.

[JMPGuitars]

I dont use them. I agree with Geoff they just add noise. I just dont see how they would benefit anything in the PI plate load resistor spot, which agrees with your own observation that you cant tell a sonic difference either.

If you want to understand, read the article I linked above. He explains exactly why it may benefit.

I didn't indicate whether or not I can tell a difference, only that I don't know because I never A/B'd them in a blind test.

Thanks,
Josh

[crgfrench]

The audio signal does not pass through plate load resistors.

Does audio signal pass through plates? Do plate resistors affect the sound the tube produces?

Did you read the article?

The signal passes through the plates but not through the plate resistors. So the value of the plate resistors matters, but composition of the plate resistors would be irrelevant.

Yes I read the article, thanks for the link. It seemed fine. Maybe not, like, "Gospel fine" but it was OK.

[JMPGuitars]

The signal passes through the plates but not through the plate resistors. So the value of the plate resistors matters, but composition of the plate resistors would be irrelevant.

Yes I read the article, thanks for the link. It seemed fine. Maybe not, like, "Gospel fine" but it was OK.

As per his article, and plenty of others, as well as public opinions of many amp nerds... In the correct position (in this case the PI plates), the carbon comps can add desirable distortion, or alter it in a likely pleasing way. The PI contributes to the overall distortion in these 18watt amp circuits. Knowing those things, you can see that specifically in that position it can impact the distortion tone that the PI produces (for better or worse).

Whether or not it's a huge impact, or even really noticeable, is another discussion. I do know that the amps I've used them in at the PI plates sound good. But to the point of the topic, I wouldn't bother with them anywhere else.

Thanks,
Josh

[geoff 1965]

i agree with Josh and RG's article in that the composite "mojo" is mostly hype,and his last words on the subject are "the effect is real,though slight"so in answer to Tim's question if you want a hiss free amp and accurate tolerance then use good quality carbon films and you could do a comparison test with the phase inverter plate resistors to see if the breakup sounds softer with comp's.in fact i'll have to try this myself now to see how much of an audible difference there is!

[crgfrench]

Here is the downfall of Keen's article:

He begins be defining "resistor distortion" as follows:

...if you put a 50V DC level across a CC resistor and a 100V sine wave superimposed on that, the sine wave will be measurably distorted by the resistor itself. We have resistor distortion.

The distortion is pretty much pure second harmonic. In small amounts, you can't hear second harmonic as distortion, only a certain amount of "sweetening" or liquidity to the tone. That's what carbon comp resistor mojo really is - the resistors are distorting, but in a way our ears like.

Fine.

And he concludes:

...The place to use CC's is where there's big signal - plate resistors, and ideally the stage just before the phase inverter. The phase inverter would otherwise be ideal, with plate resistors carrying the highest signal voltage in the amp...

And I think, Josh, you are relying on this argument. Fine.

Let me point out Keen's error:

There is no sine wave superimposed on the plate resistors in a tube amplifier.

All the plate resistors see is DC. The audio signal AC waveform goes from the plate to the coupling cap and forward on through the signal chain. It does not go "backwards" through the plate resistor and into the B+ line.

So it is impossible for the plate resistors to contribute this "resistor distortion", or second order harmonics, to the audio signal.

Keen just came to a wrongheaded conclusion.

[geoff 1965]

it must have an effect though on the tone of the distortion as the article says,yeah the ac signal does'nt pass through the plate resistor but it feeds off the plates high voltage which has passed through the resistor.i would imagine there is a difference between 240 vdc going through composite material than film,in the same way as using quality filter caps affect the tone of the high voltage B+,am i right in thinking this?

[crgfrench]

Without AC running through the resistor along with DC, there is no "resistor distortion". The whole idea of resistor distortion adding a second order harmonic requires that the resistor is in the audio signal path. And plate resistors are not in the audio signal path.

[crgfrench]

I just noticed that Danny Russell uses CCs in one spot only: the PI grid leaks. Hmm... Greta Van Fleet plays these.

Alice in Chains plays Meteopoulos, I feel like George isn't slinging "BS hype". He is a professional builder and amp tech. That said, I wouldn't use them in the input section where he indicates.

Who plays Keen's amps? I can't seem to find his builds anywhere.

[Daviedawg]

Gawsh. I missed all this while I was asleep.

A long long time ago I was told by a radio engineer who worked to keep all the BBC transmitters in Scotland on line and up to scratch (when they were valve receivers and transmitters) that every single thing in the circuit has an effect on the quality of the signal. He would know spending his working life fixing big hifi stuff with what was in the van as it were.

There are a lot of CCs in my 18 watt. I have no detectable noise from them. Whether they have a beneficial effect is totally subjective. But I like the look and I am happy with the tone I have. No science involved just lore.

They came by the bag load and I selected the closest values. But then I did have to swap out a couple when I had hiss soon after the build. So there is basis in the noise issue but it is not hard to resolve. And not all CCs cause problems. Except that in itself is a problem which commercial ampmakers have to consider. Whether you need or wish to bother is doubtful.

As a hobbyist I have time to take an empirical suck it and see what happens approach.

Dd

[JMPGuitars]

I just noticed that Danny Russell uses CCs in one spot only: the PI grid leaks. Hmm... Greta Van Fleet plays these.

Alice in Chains plays Meteopoulos, I feel like George isn't slinging "BS hype". He is a professional builder and amp tech. That said, I wouldn't use them in the input section where he indicates.

Who plays Keen's amps? I can't seem to find his builds anywhere.

This is a terrible argument. GVF is the worst thing to happen to rock and roll in at least 20 years. Their sound is TERRIBLE. If GVF played one of my amps, I'd be embarrassed. In case I'm being too vague here, I can't stand them.

Jerry Cantrell plays Friedman, Marshall, Fender, and Mesa. And even if he does happen to own one of those Metro amps (which I'd be a little surprised) it doesn't prove anything regarding the position of CC resistors.

I'm a pro builder and an amp tech. That doesn't mean I haven't bought into any hype. It doesn't mean he hasn't either. Maybe he believes the hype, that doesn't make it real. A good build quality of a good circuit with good components will sound good regardless of the resistor type...though metal film might sound too sterile. Or is that hype too? I don't know, a lot of people use MF. Now I want to build an amp with mostly MF and see if I can tell the difference or not.

Here's Aiken's perspective, and certainly more on topic for this thread:
http://www.aikenamps.com/index.php/resi ... -it-matter
http://www.aikenamps.com/index.php/technical-q-a

Thanks,
Josh

[crgfrench]

Well, there you go. It's all subjective. That's why its art after all. Peace!