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Guitarist's Tech Workshop

Lesson 8 of 18

Electricity Basics

Kurt Bloch, Ben Verellen

Guitarist's Tech Workshop

Kurt Bloch, Ben Verellen

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Lesson Info

8. Electricity Basics


  Class Trailer
Now Playing
2 Problem Areas of Maintenance Duration:14:08
3 Proper Stringing Techniques Duration:04:31
4 Proper Standard Rock Setup Duration:34:10
6 Proper Drop Tuning Setup Duration:39:49
7 Electronic Maintenance Duration:22:11
8 Electricity Basics Duration:24:06
9 Reading a Schematic Duration:06:53
10 Using a Multimeter Duration:10:20
14 Preamplifier Circuit Design Duration:28:25
15 Power Amplifier Circuit Design Duration:10:36
16 The Phase Inverter Duration:03:58
17 The Power Supply Duration:15:03
18 Final Q&A Duration:08:44

Lesson Info

Electricity Basics

This place to start talking about guitar amplifiers and to ban specifically is to just break into some real basics about electricity and how they work in the guitar amplifier, so I don't really know how much everybody's going to know about this stuff, so some of this might seem really simple and redundant, but I'm just going to start with the simple stuff anyway, and maybe some of the stuff is too nerdy as well. So be forewarned. Um, so electricity basics. So voltage voltages, the potential electricity to flow between two points. So if you have this place is more positively charged in this place they're attracted to each other, and if you give them some path for electricity to flow between the two, it will do that and that sort of ah to be thought of his potential, you have this potential for two things to flow and that's sort of the driving force behind most of this this and stuff. So a couple of distinctions between two different kinds of voltage that crop up and guitar amplifiers. T...

he most common time you talk about bolted when you think about it is a d c voltage direct current. So a common example that is a battery, a nine volt battery and you just over the course of time. That battery is nine volts it's, always nine volts from those part and, uh, and that's ah voltage, a type of voters that is used in guitar amplifiers as well, like any small device that would run off a nine volt battery tube, amplifiers typically run off of very large voltages, but d c voltages um, and then the other type of voltage that is important to talk about is a c voltage alternating current so that voltage over the course of time fluctuates, has some change. And the most common example of that is the power that comes in from the wall one hundred twenty volts a c and that's used to power everything obviously, um and but a c shouldn't just be thought of as a perfect sign e so it'll real smooth curve like that that's what the wall power that's coming in looks like a sea voltage khun b other values of signing sort of voltage or can also be a simple is something like the voltage that comes out your guitar when you pluck the string and it wiggles back and forth over a magnet that induces a voltage that is a sea it's fluctuating. And so all the fundamental behaviour of a c has to be thought of not only for the sources they're supplying, and but also the signal that you're sending through it um so this is about is math is this whole thing is going to get and I apologize, but a little bit has to be inserted. And it's it's real basic. I just want to talk about two equations that air important. So if you took a voltage, say, a nine volt battery or really any voltage and applied across a load of a resistor resistors just this device that's designed to impede the flow of electricity. But it is a path it's, a path for this positively charged area to get to this negatively charged area through the resister. So once you have that load across, the voltage source current will flow, and that current is dictated by this equation. Voltage equals current times resistance. So if you knew you had a nine volt battery and you knew you had some resister, you could then solve for the amount of current that has been flowing through the resister, um, a little bit algebra, you just would take this voltage and divide both sides of the equation by resistance, and then current with an equal voltage divided by resistance. Sorry, some math had to be done that will be handy and explaining some other stuff later. Another important one to consider is power. So power is it's, the work that's being done by this process in this case, and so the equation to solve for the power through a load like this resistor and the picture here would be the multiplication of the current through the resister times the voltage across that resistor so just some real basic stuff just to keep in mind and again sorry if that's obvious information to everybody or also sorry if that's too nerdy annoying to stare it I was going to jump right into some basics about the vacuum tube um I'll just go ahead and grab a tube out of this amplifier so I can kind of show you what's going on um a tube is just a glass sealed vacuum so there's no gas in here there's relatively nothing whatsoever except for some little metal electrodes that air residing inside the tube and so a long time ago you know about one hundred, one hundred twenty years ago they figured out that if you stick a piece of metal inside the sealed vacuum tube and you apply some voltage to it a c voltage in this case to heat it up much like a light bulb. That voltage will cause that piece of metal to boil off a cloud of electrons a cloud of negatively charged ions that just floats around in the tube so in this picture you can kind of see the cathode here is the name of that electrode that would boil off the electrons so you heat it up and it spits out of cloud of electrons that float around aimlessly in this vacuum, they don't have any destination until you apply ah positive voltage to another piece of metal inserted inside the tube that one's called anode or the plate. So basically, at that point you stick this positive charge on this piece of metal, and now this cloud of electrons that before had no destination are now attracted towards that positive anode, and they shoot up towards this has called the tube dialled in this case where you just have the two electrodes inside the sealed vacuum, and these are handy devices used for power supply rectification, which we'll get into later. But the basic idea is that you stick a positive all to john it electrons flow towards that you have current, you stick a negative voltage on it are no voltage, and again, you have no current. Those electrons are no longer attracted to the plate, and they just continue to float around aimlessly. So that was the kind of inception of the electron tube and then they figured out a new idea they could add into that mix where if you took that same kind of enclosure and then inserted a third electrode called the control grid into that mix, now you have this other piece of metal in there that you can apply different voltages, too and so if you were to stick a negative voltage say on this control grid negative with respect to the cathode the cathode boiling off these elections the plate is positive they want to shoot toward the plate but if you have this control grid that you then stick a negative voltage on it will impede that flow and the whole trick with the tri owed which is the name of this device with the third electrode inside try owed three electrodes it's kind of like that name came from so sticking a negative voltage on that control grid. Now you can actually manipulate the flow of electrons toward the plate and the real trick with amplification specifically you take a real small signal say from a guitar or really any source and wiggle it you know, pluck your guitar string it waves back and forth makes a little voltage happen put that voltage on this control grid and now you have this little tiny signal that's manipulating this larger flow of electrons from the cathode to the plate so that large current that you've now got control over you stick that across a load like a resistor and that resister has this was current shooting through it mohr unless with response to your signal and that that current spinning through that resister induces a voltage because now you got that equation we were talking about voltage equals current times resistance that current you're creating across that resister that you might have is the load for this tube is now got a large voltage exactly reflects the signal that you put on to the control grid but it's bigger so it's amplified that's amplification essentially how it works and then just another important tubes tied to talk about well concerning ah amplifiers is the beam touch road so this is really a similar idea to what you have for the tri owed but there's some additional tricks inserted into this mix. So now you still got the control grid it's still there to control the flow of electrons from the cathode to the plate but in addition you inserted thiss ah fourth electrode called the screen and the screens purpose there is too apply it sits closer to the control grid and you apply a positive voltage to that and it just helped guide the electrons toward the plane. So it's it's not the most important thing to think about, but it is a different device than the tri owed. And the real importance of it is this is the technology that's used tio make the tubes the vacuum tubes that do the job of making your speaker wiggle so it's just a more efficient way to get current into a load through a vacuum tube it's just a different type of tube that does a similar thing but more effectively for the purpose of making power translate to a speaker so continuing on with vacuum tubes it's important when you're thinking about vacuum tubes to be aware that there's pins that stick out of the enclosure of the seal vacuum tube and those pins are connected to the electrodes I've been talking about and there's many, many different types of vacuum tubes and they all comply to the tubes differently so each different tube type will have a different pin out and so people talk about tube swapping you know, dropping different tubes into an amplifier to see how they sound see what they do an important thing to keep in mind is that those pin outs are different for each different tube type so you have to do a little bit of research and google is pretty handy for finding out exactly what's on there and you could just look it up on all the information is on the interweb so this will be here on the right hand side is a diagram of the tube as we were looking at those pictures before and you can see these numbers applied to each of the electrodes within a tube over here you have the pen out of the tube and going around from this little notch that indicates the sort of place to start the counting pin one two, three four five six seven eight in this case and then you can translate to the schematic version of what the tube is over here and so that's just something that you want to keep in mind if you're doing to swapping and kind of have a look and see what's what? Make sure you don't make something blow up wait to learn the hard way just you know, see if it blows up um so that's kind of just real basics about to lose a lot more to talk about that, but so just some more, um, devices involved electricity in general, the resistor is the most common one and as you said before, it's ah device whose purpose is to impede the flow of current and resisters are used for all different kinds of things, just some important values to consider when you're talking about resistors, obviously, the resistance the amount of impedance that, uh, resister will present to the potential flow of current is the most important one to consider, but there's some other ones as well. So you need to know exactly how much power you expect this resistor to dissipate if you're going in and replacing resister from an amp say in this particular position an amplifier. You know, if you do the research or measurement and find out that that resistor is going to be dissipating about of a lot of energy, a lot of power, you would make sure you you're replacing that resister with the correct wattage handling resister so they respect for that you look him up and they tell you how much resistance how much power can handle um and those are the two main ones to consider and resistors that really just they get larger when they can handle more power it's just a major of how much heat the thing khun dissipate um there's lots of different types of resisters they're made from metal oxide they're made from metal film they're made from carbon film carbon composite there's a lot of debate about the sonic benefits of each of these types of resistors and I don't delve too much into that that's sort of world of kind of cork sniffy this resistor has that certain something this was mr type has I mean there's there's something to it for sure but the most important things to consider our what does this resistors value and how much power can it dissipate and then from there once you've got things working, then if you want to go drop in different types of resisters in to do, um, that sort of experiment by all means, but I'd say the design of a circuit is much more important than the type of component that you're placing in it that's that's my personal opinion okay, another important component that you'll see many oven an amplifier, the capacitor so the capacitor is a device that stores charge is kind of the typical description of what a capacitor does, but capacitance is a phenomenon that exists between any two conductive materials. So you've got a piece of metal here and a piece of metal over here there is capacitance between them it's just a physical phenomenon it's it's magic you know it's just a weird thing that kind of like gravity I guess you might describe, you know, gravity, you can't prove that exists until you drop something and it's the way you describe what you're experiencing when you see that happen capacitance is like that, and I think that the best, most useful way to think about capacitors when you're talking about back into pamela fires is you can think about a capacitor as a frequency dependent resister. So where a resistor applies a certain amount of resistance to no matter what you throw in it. If it's a d c source going across a resistor, it sees how x amount owns whatever the impedance is. If you apply an a c sourced to that resister it's still the same amount of owns if that a c sources wiggling very slowly or very fast, it makes no difference, but a capacitor is not like that a capacitor presents a varying impedance, depending on how fast what you're putting across that wiggles so d c like a source that enable battery will not get through a capacitor it blocks it very slow moving signals they're slow moving a c signals will see a capacitor as a large large resistance at a brick wall in some cases or just a very large resistance and a very fast moving signal across that same capacity if it's wiggling fast enough for a given capacitance it will see that same device as a short or as a very small resistance and that's a tool we can use for lots of different things within an amplifier again there's lots of different types of capacitors there's a little bit more consider they don't rate them for power but you do need to consider voltage so if you expect to see a certain amount of voltage across the capacitor you need to make sure that the capacitor is rated for at least that amount of voltage and a lot of people say be a bit conservative maybe rate a capacitor for twenty percent larger than you expected to see and its most high voltage scenario uh another important thing to think about capacitors is some capacitors are not polar meaning that there's two terminals coming out of the capacitor and it doesn't matter which way you flip it when you apply it into a circuit but there are other capacitors that air called electric electrolytic capacitors that are polarized and it becomes important which side you apply a positive voltage which side you apply and negative voltage. So you have to be aware that if you're replacing the capacitors say or designing something you need to know which side of of the capacity is going to see a positive voltage with respect to the other side and let's see moving along. Another important component that you see in amplifiers is the induct er and the induct er much like capacitor is the first thing to say that it is again it's just a physical phenomenon it's not it's a device that does inducted swell but induct ints itself is just inherent it's inherent phenomenon with any wire you have with a current through it if you stick a current through a wire, it spits out a magnetic field that if you were to try and change the direction of current through that wire that field opposes that change in current that's attempting to happen. And so they figured out that if you take this wire and coil it up like you see in the picture here that coil wire now exhibits better inductive meaning it's even harder to make the flow of current change directions across that that in dr and now if you take that coil of wire and stick it around a magnet now the magnet even further amplifies how much induct ints that device has and there's lots of different ways that these crop up in amplifiers but again similar to the capacitor the way to think about induct er that's useful in my mind is the doctor is basically another frequency dependent resistor and in this case it works the opposite way so where is a capacitor would see low frequency signals that air wiggling very slowly as a very large resistor the induct er sees very low frequency signals and d c as a short they can shoot right through it but very fast wiggling signals they hit that in doctor like a brick wall so they're kind of two sides of the same coin and again used for lots of different things within an amplifier if you take that idea about inducted it's a step further take two coils of wire wrap him around the same magnet. Now you have what's called the transformer and works the same way except that magnetic field that spit out by one coil of wire around a magnet that magnetic field find its way into the second coil and that second coil now develops a voltage that can be taken off and used elsewhere if you have a certain amount of turns around this magnet on one side and apply a voltage to it and you have a second coil that has a different amount of turns across that magnet that turns ratio between what's called the primary beside you're applying the voltage to and the secondary the side that's coming out of the other end of the magnet now you khun dictate whatever vaulted you want to see this only applies to a c again in doctors d c shoots right through but a c is the thing that spits out the magnetic field that makes this coupling between a primary side of ah transformer and a secondary side of a transformer it's a really good diagram but uh but the basic gist is transformers are very useful within ah amplifiers for a couple of different purposes the main one, as you know, the way you see transformers used all over the place for a power distribution or any other device that needs a power supply is the power transformer. And so every guitar amplifier has a power transformer, even solid state amplifiers. And the idea here is that you take a sea maine's voltage one hundred twenty well, stacy from the wall and you stick it on this magnet across this coil of wire and it spits this flux into the magnet which then couples into a secondary winding that secondary winding then supplies the voltage is that the amplifier needs, you know, amplifier is going to need many different voltages for different purposes so you might stick one hundred twenty volt the wall gives you across this transformer primary and you might have two or three different secondaries and they all have different purposes so, for example, to make that tube phenomenon happened where it heats up, in boils off that cloud of electrons. You have what's called the filament, the filament it's like a light bulb filament. It just heats up the cathode to spit off that cloud of elections, but that filament only needs six point three votes a c. So you've got on the primary side this one hundred twenty volt say. See, you need six point three bullets a c so using that turns ratio from the primary side to the secondary side, you can dictate what bolted you get out of the secondary and therefore have a source for this voltage to heat up all of your tubes. But then you also need ah high voltage d c battery to make to balance work and that's. What makes the tubes have ah, like a battery to work off of, and that needs to be a very, very large dc voltage. Say, on the order of five hundred bowls, so you've got one hundred twenty both a c coming in you need. Five hundred bullets d c on the output well how to make a d c we'll get into that later but just you know you're going to need something much larger a seaside so you have another coil of wire on that secondary that's going to spit out that large voltage that you need and it's that induct ints across the magnet and the couple in between the two coils that makes that happen nerd herd and the other really important place that transformers air seen within a guitar amplifier is what's called output transformer and it's a completely different deal so the power transformers job was to make aa battery for your amp to make the tubes heat up basically to make the thing function to give it the supply it needs to operate the output transformer on the other hand, is actually dealing with your signal the single that your guitar is is creating and the single that your amplifier puts out and specifically it's designed to translate the guitar amplifier to your speaker and there's a lot more to talk about that we'll get into that later but just important to consider that this is a this is a tool used to uh move to propagate your guitar signal so the a c signal that's finding its way into this magnet is not a power supply a c this is your guitar signal on dso there's lots of things to consider concerning output transformers to make sure that they sound good. It's a little bit more of a important component as faras, you're the sound of your aunt.

Class Description

Performing a proper setup for your guitar can seem like a dark art requiring a copper chalice filled with incense. Reading a schematic of a tube amplifier can seem like you’re staring at ancient Sanskrit. Guitar and tube amp masters Kurt Bloch and Ben Verellen are here to help.

In this two-part workshop, Kurt and Ben will show you exactly how to get the best sound out of your gear.

In part-one Kurt will teach the basics of setting up your guitar – you’ll learn about:

  • Truss rod adjustment
  • Bridge and nut adjustment
  • String gauge and playing style
  • Guitar maintenance and upkeep
  • Guitar electronics and pickups

Part-two is your primer on tube amplifiers. Kurt and Ben will explain how they work and show you how to keep them sounding great. You’ll learn:

  • Tube biasing
  • Block diagrams and understanding schematics
  • Basic amplifier maintenance
  • Capacitor, resistor, and transformer replacement
  • Speaker repair and power-matching

Kurt Bloch is not only Gibson Guitar’s in-house guitar guru, he’s a legend in the Seattle music scene. He plays in The Fastbacks and Young Fresh Fellows and has a producer credits for his work with The Presidents of the United States of America and Tokyo Dragons. Ben Verellen started Verellen Amplifiers in 2000 and now has a full-time staff churning out hand made custom tube amplifiers for some of the most respected artists in rock and metal. He also fronts Helms Alee, a rock band based in Seattle.

Don’t get caught with crappy tone and blown out speaker – let these two masters show how to take care of your gear and get the best possible sound.


Patrick Marc

This is a fantastic course. I was forever looking up Youtube videos on how to set up all of my guitars for different things, and opinion varies wildly on-line, so it's really great to have these videos detailing the entire process in clear and easy terms. The information on the amplifiers is intensely interesting too. Fantastic!

Alan Williams

Excellent course. Slow start with the guitar set up but Kurt knows his stuff so worth watching it to the end before deciding you don't like it. I came across valves (tubes) at the age of 12 (I'm 66 now) and it was a great refrresher for me. Ben really knows his stuff but he can put it into layman terms that are easy to understand. I definitely recommend this course.

Andrew Synowiec

I bought this course for the amplifier section and skipped straight there. It's fantastic. Right at the perfect level for me, a newbie DIY-er with a few pedals, a kit amp and an Electronics 101 course under my belt. Well done! I'll update my review if I have time to watch the guitar section.