Loadlines

[Nick]

Ok, its been suggested that we have a go at describing load lines. The link suggested

http://diyparadise.com/tubeloadline/tubeloadlines.html

Does a good job of describing them, but does miss out some of the interesting things that can be got from the lines (Ra, gm, mu, expected distortion and so on).

If we did have a go at this, what would people want?

Maybe a set of lines, then a description, then any questions, then more descriptions. What peeps views on this?

Or should we go further back and start with the basics, current, voltage, resistance, capacitance, inductance?

[Darren]

Could I suggest we have sections and make it a permanent reference for the different areas/aspects?

Wiki has some interesting write-ups perhaps link to such places as well?

[david C]

thanks Nick
from my point of view it would be nice to have an overview of the basics, it would then put it all into context

[Nick]

Yes, I was thinking about using links to Wiki to provide more detailed info.

What would make me bad at this is that I will just witter on, and not notice if its making sense.

Also there is a danger that I will end up doing what the steriotypical brit does when oversees. I will forget that people find maths a problem, and assume that by shouting it will somehow make it easyier to understand.

I am not sure just how much I can explain without falling into maths, my fault I know, but that doesn't help. Maybe we need our local professional educator to show the way? How can I explain Ohm's law and simple circuit analysis without maths Steve?

[Darren]

Thinking about it, perhaps not in the same line as other sections here.

I think it ought to be locked to general replies, otherwise the real info would soon be lost and threads do tend to wander off subject.

Maybe appoint some editors?
Difficult I suppose.

[Darren]

How can I explain Ohm's law and simple circuit analysis without maths Steve?

Maybe, use water as a metaphor? I always found that helped myself in the begining.

I'm only speaking out loud, if I'm off track just say. I won't sulk too much

[colin.hepburn]

Hi All

Well for me it would be better and more helpfully to start again back at the basics
I have found this spreadsheet that I thing would be helpfully but doesn’t explain things but it sort of works it out for you OK this isn’t teaching you but may help
Tube data Most used Tube formulas version 1.0

Here on the download page http://www.platenspeler.com/download/uk_index_body.html

[Nick]

Maybe, use water as a metaphor? I always found that helped myself in the begining.

Yes, I think that can help.

[Cressy Snr]

Maybe we need our local professional educator to show the way? How can I explain Ohm's law and simple circuit analysis without maths Steve?

Hi Nick,

You can't.

In my experience in schools it is not the maths itself that bothers most people. After all 99.9% of the stuff we need for valve circuits only involves the four basic operations, ie addition, subtraction, multiplication and division.

The formulae for ohms law, gain, distortion etc are simply things that need to be learned, remembered or looked up if the person has forgotten them.

However when it comes to the application of those abstracts to real life problems, that's where the trouble starts. For example I can just about remember the formula for solving a quadratic equation and have nicked an image of it below

What the hell am I supposed to do with it though? I don't even know what the terms refer to and this kind of "sticker shock" is, in a sense, what beginners to valve electronics are up against.

What I think people need to be shown, is how to apply these rules to practical problems that will give concrete results; for example

" this is how you draw a loadline for a valve with an anode resistor using those ohms law equations"

"now you have drawn the line, this is how you interpret it"

"This is how the loadline for a valve with a transformer or choke load differs from the above, here is how to draw one of these. The principle is the same but you start from a different point"

"Now we can draw proper loadlines, here is how to design for low distortion in a preamp, input or driver stage"

Why do we need an output transformer?

What is turns ratio and how does this cause reflected impedance?

"Now we are going to make what we just learned above useful by using what we now know to design a power stage for a popular valve by showing how our knowledge of how to do loadlines can enable us to choose the right TX for the job"

It could be set up as an FAQ section with no replies allowed except peer review by PM.

All SE of course to start with.

I think that by working gently, in the order I have outlined and putting links for further reading at the end of each section, the panel could help other less experienced members get to grips with the basic stuff.

On the question of what is current, voltage and resistance.

I think people are going to have to do a bit of homework and read up on these themselves, by following some links. This will give them the tools needed to understand the design walkthroughs. Otherwise it is all too easy for the tutor to get bogged down with fundamentals and achieve nothing worthwhile with the students. The students need to think of it as the required, essential preparation that will allow them to do the good bits.

Steve

[Nick]

Thanks for that view steve, I think you are right, but to take up a point, maybe it might show a problem.

On the question of what is current, voltage and resistance.

The problem is that once you understand those three terms, then the rest should fall into place. Maybe thats a result of my equivilant to dyslexia. I can't remember things, never have done. But I can work them out, I could do maths and physics at school, coz you didn;t need to remember, you could always derive the equations. Couldn't do chemistry, as that needed memory.

Now my point with this reference to my schooling, is that if you know what E, I and R are, and their relationship in Ohm's law, it all can be worked out. Once you add both of Kirchhoff's laws to that, just about any DC circuit can be analysed.

My question is should we start with that, as IMHO, once they are understood, then the rest, especially load lines fall into place, but without them, its all guesswork.

Example question: Why does the slope of the tangent to the grid curve at a chosen operating point equal the plate resistance? Answer, cos its just Ohm's law. But I am not sure how clear that will be untill its understood that resistamce is just the third part of any relationship between current and voltage.

I hope you see my point.

[Cressy Snr]

I can see your point Nick and there is, I think, a way around the problem.

Set up two threads; one teaching the basics of electricity, Ohms Law and Kirchoff's laws with suitable links to easily digested articles (no point re- inventing the wheel if someone else has already done the donkey work) sorry about the mixed metaphors

The other thread can be the practical valve electronics stuff with a disclaimer that if the reader does not understand the fundamentals then they ought to start with the first thread before trying to design anything on their own.

By splitting the advice into two bits, distinct and logical stops along a route to understanding are being created for the student. That way the learner is being provided with exactly what they have to know about, in order to progress from the first level to the second.

Steve

[Nick]

Ok, good idea, I will start to put a first draft together.

Even though its a forum, we can still alter the text, by editing, and removing posts suggesting changes after the changes have been put into place.

If you see what I mean.

[david C]

the problem I have is I can follow a circuit and build an amp or whatever but in all honesty cannot tell you how it works, if I had to modify the circuit I would be lost, for example I don't know how to float the heaters or why I should have to,

I have great admiration for Steve and Andrew as they seemed to have grasped the principals, that's what I want to understand,

simple maths like ohms law are not a problem

[Darren]

David, I think this is the sort of thing that will be covered, eventually.

Floating the heaters is just about not grounding the negative side.

Easiest way to think of it is to imagine you are heating with a 6V or 12V battery. Connect the + & - from the battery and don't ground the neg with the rest of the circuit. ie leave it floating.

All you really need to know to make a valve operate is it working range.
ie, B+, bias voltage and ma draw. You'll find that from such sites as Duncan Amps http://tdsl.duncanamps.com/tubesearch.php
I would suggest downloading TDSL from the same site.

With load lines you can take a deeper look into the valve characteristics and begin to design your own circuits by having a better understanding of what you are likely to achieve with each valve stage. You can also look at the data graphs and maybe pick a different set of operating conditions to suit your particular requirements.

Paul barker did once teach me how to read load lines, and it wasn't that hard to grasp. But I freely admit that is not how I build amps these days. I simply look up the operating data and and slap a string of valves together to make an amp.
Despite the fact I have built many amps now, I feel I still only have a grasp of what's going on. But I do only build simple circuits.

Some of us have very different ideas on how to build our circuits, I'm very much a minimalist. Less is more sort of thing. Others like the challenge of complicated ideas to tax themselves with and no doubt find this very rewarding.

I certainly look forward to future tuitions and to gain a better understanding.

[Nick]

simple maths like ohms law are not a problem

Ok, thats great, all you need to to be confidant and learn how to apply that simple maths.

A lot of whats involved is just being about to see through what looks complicated and break it down into simple parts that each individually can be understood, and from, that understanding the complex comes.

Maybe we should start with simple definitions, DC circuits, Ohms law, work onto Kirchoff and see how that goes?

Its AC where it gets harder to avoid maths, but lets see how it goes.