130 Ohm 3w ceramic explanation

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130 Ohm 3w ceramic explanation

Post by davemojo »

Hi All,

On some build I see the requirement of using a 130 Ohm 3w ceramic
It doesn't seem to be so easy to find it in Europe since my resistors knowledge is limited I may need an explanation and what alternative solution

Is a metal Oxide 130 Ohm 3w the same? Why a ceramic, for heat dissipation ?

If I want to get that one as written on the guide where can I get here in EU?

Now a resistor is a resistor so possibly another type non ceramic may suite here for the 18Watt build?

Unsure I am moving from carbon composite to carbon film or metal film for all the other resistors needed

Other questions is it is possible to mix carbon composite and carbon film or metal film, I need to understand the requirements on a typical 18Watts build and how can I freely move between those resistors utilization

Thanks
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Re: 130 Ohm 3w ceramic explanation

Post by Bieworm »

hi

on what build do you see a 130R 3W resistor? And where is it used?
if it's the cathode resistor on an 18 watt then 130 Ohm is usually biased too hot. We use often 180 Ohm 5W. The higher the wattage , the safer.. so it's probably better to use 10W. Make sure you have some variations like 150 - 180 - 200 - 220 Ohm.

The carbon comp resistors are only beneficial (to a modest level) on the plates of the PI. As Josh pointed out earlier, you MUST use 1M MF resitors on the inputs. Those are pretty crucial. The other resistors you can choose-mix-blend between MF CF and MOx. Though it looks nicer when all resistors are the same brand and type.. apart from the wattage.
FWIW I use MF resistors on every path to a grid
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Re: 130 Ohm 3w ceramic explanation

Post by davemojo »

Bieworm wrote:
Thu 03/18/21 7:52 am
hi

on what build do you see a 130R 3W resistor? And where is it used?
if it's the cathode resistor on an 18 watt then 130 Ohm is usually biased too hot. We use often 180 Ohm 5W. The higher the wattage , the safer.. so it's probably better to use 10W. Make sure you have some variations like 150 - 180 - 200 - 220 Ohm.

The carbon comp resistors are only beneficial (to a modest level) on the plates of the PI. As Josh pointed out earlier, you MUST use 1M MF resitors on the inputs. Those are pretty crucial. The other resistors you can choose-mix-blend between MF CF and MOx. Though it looks nicer when all resistors are the same brand and type.. apart from the wattage.
FWIW I use MF resistors on every path to a grid
I'll be using on next build the MF resistors

3 questions actually
1) 130ohm 3W ceramic
I can use 5w or 10W fine but is a FM resistors why they call it ceramic?
Can you point me to buy one in some EU shop to see which equivalent match similar one?

2) aluminum electrolytic 50uf and sprague 50uf are the same similar what's the difference and why they call it like that, is just a brand Sprague atom?

3) I have a Sprague atom that is 250uf can i use it replacing what they call here 250uF 25V bipolar electrolytic?
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Re: 130 Ohm 3w ceramic explanation

Post by Bieworm »

1. The ceramic resistors are those white wirewound brick shaped power resitors. That white material IS ceramic.

2. Sprague atom caps are a brand of electrolytic caps

3. Yes. If the voltage rating is at least the same, which will probably be the case. But 250uf is not what's recommended for 18 Watt amps. We use higher capacitance, preferably 2200uf for better low end response. That is if it's about the power tubes cathode bypass cap... which you're probably referring to..

You should use the layouts from the download section on this site. Check the modern classic or the tremolo TMB documents... trust me, those are the superior versions of those 18 Watt builds
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Re: 130 Ohm 3w ceramic explanation

Post by TriodeLuvr »

I disagree regarding the use of metal film and carbon film for grid stoppers. The primary requirement of a grid stopper - if stopping oscillations is its actual purpose - is to reduce the Q and inductive reactance of the grid circuit. The spiral construction of film resistors degrades their effectiveness in this regard, and I have personally witnessed circuitry in which their use encouraged parasitic oscillations that did not exist when a carbon comp was used.

Another aspect of this is that a series grid resistor conducts an almost infinitesimally small amount of current in normal operation, only what is required to impress the signal voltage across the internal capacitance of the tube. This leads to two conclusions; first that the resistor does not contribute audible noise to the signal, and second, its value is only significant in terms of reducing the Q of the grid circuit and (as a secondary purpose) creating a response contour that attenuates higher frequencies. Neither of these functions is critical as regards the resistor's value; large variances in terms of resistor tolerance have little practical effect. A 10K 5% resistor that drifts to 12K (+20%) will not materially effect the result.

Just to be clear, I understand that the term "grid stopper" is used differently by guitar amp aficionados than by those working in other areas of electrical engineering. Guitar amplifiers are typically filled with tubes that have little propensity to oscillate, but which may exhibit relatively high values of Miller capacitance. Therefore, the resistor is not needed so much to inhibit parasitic oscillations as to tailor (attenuate) the high frequency response of high gain circuits using high-mu triodes like the 12AX7.

The bottom line is that carbon comp resistors are the most appropriate for this purpose, despite their potential shortcomings in other applications. At best, they are the most effective for preventing parasitic oscillations. At worst, they do no harm.

Jack
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Re: 130 Ohm 3w ceramic explanation

Post by JMPGuitars »

TriodeLuvr wrote:
Thu 03/18/21 1:11 pm
I disagree regarding the use of metal film and carbon film for grid stoppers.
I'm going to test this. I use a 10K MF in my tube tester on the grid to combat PO, and it works. BUT I want to see if there's a measurable difference using CC.
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Re: 130 Ohm 3w ceramic explanation

Post by TriodeLuvr »

I don't think there's a simple way to objectively quantify the advantage of carbon comp for this purpose. For one thing, the propensity of a particular stage to oscillate depends on both the tube type and the layout. And then there's the issue of measurement. I've seen parasitics that only appear on a fractional portion of the waveform, a phenomenon I attribute to the instantaneous change in loading that occurs over various points of the signal. I have occasionally been able to see this with a high frequency scope, but it's much more likely to be detected with a spectrum analyzer. For purposes of verifying cleanliness across the wide range of tube types and circuitry we use, a SA good to at least 1 GHz is required. Even then, the results only speak to the specific circuit under test. It's simpler for most builders just to use the carbon comp at the grid and not worry about this aspect of the design. Again, it does no harm. :)

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Re: 130 Ohm 3w ceramic explanation

Post by JMPGuitars »

TriodeLuvr wrote:
Thu 03/18/21 9:53 pm
I don't think there's a simple way to objectively quantify the advantage of carbon comp for this purpose.
Ah, but there is.

This is what an oscillation looks like on a tube trace:
EL34M.jpg
No matter what test I did, I couldn't get a smooth trace without the grid stopper. Granted there were other modifications as well, but the grid stopper made a difference.

Here's a more intense trace with the CMF resistor in place:
EL34 MF Grid Stopper.jpg

I will test this by doing the same test with both resistor types, and no grid stopper resistor, and see what the results are. If the grid stopper resistor and it's type have an affect on the PO, the results should be obvious enough.

Thanks,
Josh
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Re: 130 Ohm 3w ceramic explanation

Post by davemojo »

You guys are very technical on electronics
self method studies can be very challenging over just a simple book

I was wondering about online courses or with some simple words where can I study and get the right level of knowledge online or via which possible training if any exist? Of course not a general electronics training my purpose is to build Good Amps for myself and possibly who knows opening some little private local business in the future

In other words I am fascinated since building stuff has always been my number one thing in life. I have been playing music for a little while now, but I am very handy on building all kind of things. I started with computers long time ago I am actually HW specialist for Dell but understanding about Amps and electronics is not quiet the same thing

Surely the old Amp from the 60s were made with carbon composition and not MF

So are we talking about a better modern way to get a better sound? The Amp of that time were noisy that is for sure the idea of recreating a vintage amp is great.

Thanks
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Re: 130 Ohm 3w ceramic explanation

Post by TriodeLuvr »

I'll say again, the situation is much too variable for any single test to be meaningful (and certainly not conclusive) other than as it applies to the specific tube and layout. The need to eliminate inductance at the grid is a concept well understood among RF engineers, and I have witnessed the empirical results. I can also tell you that the trace you see of the oscillating tube is not representative of all oscillating tubes. There are simply too many variables. It's probably difficult to persuade a 12AX7 to oscillate, but the carbon comp at the grid remains good engineering practice. You know, this situation isn't too different than the ground bus soldered onto the rear of the pots. The fact that it doesn't create a problem in one particular amplifier does not create a model for success.

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Re: 130 Ohm 3w ceramic explanation

Post by TriodeLuvr »

davemojo wrote:
Fri 03/19/21 10:53 am
The Amp of that time were noisy
Well, no. Amps of that time are noisy now. I was around when amps from the '60s were new, and whatever noise was present generally came from the tubes themselves. Components degrade over time though, and tube circuitry needs more regular service than solid state to maintain good performance.

I'm not sure the best way to learn basic electronics as it applies to guitar amps. I built my first tube circuit around age 12, then obtained a ham radio license a couple years later. There's a huge amount of basic electronics theory pertaining to tubes and passive components in older ARRL (ham radio) handbooks. You should be able to pick one up at a reasonable price on the 'Bay. Look for a 1964 edition or earlier for good tube theory. There's quite a bit of good theory specific to guitar amps at Valve Wizard and other sites. However, you need a more generalized understanding (such as found in the ARRL Handbook) in order to grasp the more advanced principles presented there.

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Re: 130 Ohm 3w ceramic explanation

Post by JMPGuitars »

TriodeLuvr wrote:
Fri 03/19/21 10:57 am
I'll say again, the situation is much too variable for any single test to be meaningful (and certainly not conclusive) other than as it applies to the specific tube and layout.
We're talking about the theory regarding which resistor type is better for blocking PO. I know which tubes I have, and what test conditions are more susceptible to PO with them. Multiple tests will be done with each relevant variable in a controlled environment.

Creating a controlled and repeatable test is science. Getting repeatable results is science. Generalized statements, and "empirical" experience is anecdotal evidence, and doesn't outweigh what is measurable, and is certainly not more meaningful.

The simple fact is that if your statement is correct regarding CC resistors being better at blocking PO, then it will be seen in the results of these tests. If it doesn't perform better in these tests, then it simply isn't better. I'm going in with an open and curious mind. We'll see what happens. Assuming I can get the tubes to oscillate. 😉

Thanks,
Josh
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Re: 130 Ohm 3w ceramic explanation

Post by TriodeLuvr »

I just want to mention another site that can be really useful for learning, once basic electronics is behind you. It's called "Fun with Tubes," and it's operated by a guy named Max Robinson. I've had a few conversations with Max in the past regarding tone controls, and he's a really smart guy. His site has only a smattering of guitar-specific theory, but it's a gold mine for generalized tube-type audio circuitry and explanations. It's definitely worth bookmarking and exploring when you have time.

https://www.angelfire.com/electronic/funwithtubes/

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Re: 130 Ohm 3w ceramic explanation

Post by davemojo »

TriodeLuvr wrote:
Fri 03/19/21 10:44 pm
I just want to mention another site that can be really useful for learning, once basic electronics is behind you. It's called "Fun with Tubes," and it's operated by a guy named Max Robinson. I've had a few conversations with Max in the past regarding tone controls, and he's a really smart guy. His site has only a smattering of guitar-specific theory, but it's a gold mine for generalized tube-type audio circuitry and explanations. It's definitely worth bookmarking and exploring when you have time.

https://www.angelfire.com/electronic/funwithtubes/

Jack
Thanks Jack I followed already a lot of youtube theory about guitar amps and circuit.
I bought a book last year the basic principal of Circuit with full explanation of how a circuit with tubes works, resistors and capacitors explanation and I got addicted already.

I have seen Josh layout it is a lot simpler than the one I am following, the Stewmac, which uses the technique of soldering over the pot, and I agree is not good practice.

The current build I want to finish as it is, I will add the bleeding resistor on the filter Can a 220K 1 Watt to ground, as the only different part not listed on the Stewmac project .

My next build is 1x Celestion greenback 18Watts This one for my guitar, yes I still play guitar even if my main instrument is Organ /Keyboard.

hurray
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Re: 130 Ohm 3w ceramic explanation

Post by davemojo »

So this is how far I went with Turret

Is missing the 50uF 50V Sprague Atom between the 10nf 630v yellow Dijon and the 820 Ohms .5W resistors this is about in the middle of the turret board. i'll add it as soon as i get it on Monday since there was a mistake and i had a wrong one.

I am about to add 130 Ohms 5 watts resistors (ceramic) is the white one in picture, that is the one I meant and I believe is correct one, however I am getting on Monday an 150 Ohms 10 watts ceramic resistors.

This is for the Bias correct?
What happens if I follow my layout that says to add a 130 Ohms 3 Watts and instead I put the one in picture which has same Ohms but 5 Watts, is actually better since there are less chances to overheat?

If I add the 150 Ohms instead 10 watts, changing it with an 150 Ohms will cause issues, or is still better?
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Re: 130 Ohm 3w ceramic explanation

Post by JMPGuitars »

5W or 10W doesn't matter.

The only thing that matters is that you bias correctly. You can use this calculator to determine that: https://robrobinette.com/Tube_Bias_Calculator.htm

You want to bias the tubes between 75 to 85%. Assuming a typical transformer, you probably need 180 ohms, but you can measure and determine that later.
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Re: 130 Ohm 3w ceramic explanation

Post by davemojo »

JMPGuitars wrote:
Sat 03/20/21 7:30 am
5W or 10W doesn't matter.

The only thing that matters is that you bias correctly. You can use this calculator to determine that: https://robrobinette.com/Tube_Bias_Calculator.htm

You want to bias the tubes between 75 to 85%. Assuming a typical transformer, you probably need 180 ohms, but you can measure and determine that later.
Thanks Josh, I will check on that too.

So I bet that if the Stewmac build (Let's leave aside if is a crap building option :lol: ) but I would assume that if they made that build with in mind the consideration of correct Bias so it would mean that 130 Ohms 3W suggestion should be the correct Bias based on that build?
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Re: 130 Ohm 3w ceramic explanation

Post by JMPGuitars »

davemojo wrote:
Sat 03/20/21 7:54 am
Thanks Josh, I will check on that too.

So I bet that if the Stewmac build (Let's leave aside if is a crap building option :lol: ) but I would assume that if they made that build with in mind the consideration of correct Bias so it would mean that 130 Ohms 3W suggestion should be the correct Bias based on that build?
Nope. For one thing, most of the kits around are based on dated variables. For example, source AC was lower 40 years ago, but they still just copy the same components and values. Higher source AC = higher voltages in your circuit.

Don't trust the kit, trust the math. Do the math and adjust the kit.
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Re: 130 Ohm 3w ceramic explanation

Post by zaphod_phil »

JMPGuitars wrote:
Sat 03/20/21 8:32 am
For one thing, most of the kits around are based on dated variables. For example, source AC was lower 40 years ago, but they still just copy the same components and values. Higher source AC = higher voltages in your circuit.

Don't trust the kit, trust the math. Do the math and adjust the kit.
Hear, hear!!
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