Vacuum Tubes: Episode 1 - The Basics and the Diode

today I want to talk about something that's always fascinated me even since I was a little kid and that is that's vacuum tubes I just I think there's such cool looking pieces of technology and they have really unique shapes and they come in all sorts of shapes and sizes with different purposes and they emit these really cool blow and you can see that even with these right here that they're glowing this really cool orange as a kid I had no idea what any of that was what any of it did or any anything at all and lately I've been getting into it I've been starting to read a lot more about vacuum tubes I'm starting to learn a lot more about vacuum tubes and as you can see I have quite a lot of vacuum tube projects currently going on and so I thought it would be fun to kind of take you guys along with me as I explore and play with these vacuum tubes but there's always been a couple things that have really terrified me about vacuum tubes and that is the incredibly high voltages that they run it even as a kid I knew that you know vacuum tubes would run it over a hundred volts and that was dangerous I'm a bit accident-prone and you know I didn't really want to hurt myself so I kind of stayed away from them but recently I should have playing with them at low voltages and to my surprise vacuum tubes seem to work pretty well at low voltages and later on we'll take a look at how they do that and what's going on at the low voltages that I'm working at but first we kind of need to understand what is a vacuum tube and so the easiest way to do that is to take a look at probably the oldest most easy to understand vacuum tube ever and that is well the light bulb and I know what you're saying this is this is not a vacuum but hear me out there's a lot more in common with this than vacuum tubes then you might suspect I mean we all know that a light bulb is a vacuum right when we cry should it no longer works and if you were to somehow break the glass but leave the filament intact the second that you powered it up the filament would burn out immediately so that vacuum is necessary for the filament to emit the light and the history of vacuum tubes actually is connected very closely with light bulbs and that's because one of the primary principles that vacuum tubes operate on is called thermionic emission and it was discovered by several people independently while they were trying to discover why their light bulbs were failing early and why they were starting to blacken they were finding black deposits on the inside of the bulb trying to figure this out led to the discovery of thermionic emission and what thermionic emission is is when the filament inside the bulb gets hot enough it starts to throw off electrons and those electrons floating around inside the bulb are looking for a positive source to be attracted to and that is the basic principle behind vacuum tubes if we have the filament heating up and throwing off electrons if we can just stick another plate in there that's positively charged it can attract those electrons and then we have a circuit being made and this is actually how the first diode vacuum tubes worked so let's pop over to the bench right quick and take a look at some diode vacuum tubes that I have and the differences between them and take a look at how they work so first things first let's just take a look at the light bulb this is a really small light bulb that's intended for use in pinball machines it just happened to be one that I had laying around and they run a pretty low voltage I think this one's rated at about 6.8 volts or something like that so I have my little bench power supply here and we can go ahead and hook that up and and maybe get in you get a little view of how this thing illuminates so if we turn the bench power supply on you can see that we're pulling we're at half a volt or pulling you know really really low amperage but our like light isn't coming on and that's because it's rated for six folds so as as I start to bring the voltage up oh you can see we're starting to get a little bit of a glow out of it there and that's only at 1 volt 1 point 6 volts more voltage I pump through it the brighter and brighter it gets don't we get up to about 6 volts here I'm go ahead and stop at about six point three volts and you can see that's well that's that's pretty bright that's putting out a good amount of light and so that's that's a light bulb well we're all really familiar with how light bulbs work this is this is nothing really new here but let's take a look at what's actually going on here we just disconnect this that out of the side and then our a little light bulb there what we have is we have a filament that filaments actually made out of tungsten so that comes up and then we've got this little circular filament here and I'm putting a positive voltage into one side and putting the ground on the other side and and as the voltage gets up high enough that starts to glow and and put out light and this filament is actually almost identical to the filaments that are used in vacuum tubes the constructions a little different but the concept is pretty much the same and what we talked about was thermionic emission and so as this filament gets hot it starts to let off little electrons so the little electrons start to fly off the filament here and they don't really have anywhere to go unless we put an extra plate up here and we give it a positive voltage all right so if we give that plate a positive voltage now these electrons going to be attracted to that plate and that's how we create a flow but we have kind of an interesting situation here you can see I've got positive voltage here possible to chair and ground here and this has to run on a very specific voltage but we can run really high volts on this you know 100 200 volts or so on and well that would just fry our little filament and so what happens is that we create two separate loops here alright so we have our filament loop and then this is the little power supply over here on the filament and then coming off of this we have another loop and then we you know within this loop we can put our load or whatever and it goes all the way back around alright so because we have two separate loops and these loops don't actually ever share anything except for this one little point right here the voltage from this loop never actually makes a complete circuit through the filament as a matter of fact all it's ever doing is just borrowing the filament to let electrons leap up this way alright now what's really really interesting about this is that it's the heat that is required for thermionic emission to work so this has to be hot for the electrons to come off of it all right and so if there's a positive voltage up here the electrons go to the top but what if we take this positive voltage and we change it to a negative voltage and we put a positive voltage down here instead well what this is trying to do is it's trying to make electrons go in the opposite direction but because this plate is not heated up those electrons aren't leaving the plate so that means that currents not going to move in that direction and and what this is is a diode plain and simple and we remember our basic electronics a diode is essentially a one-way it allows current to flow in that direction but not in that direction and in that same way the current the electrons are allowed to flow in that loop but they're not allowed to flow in this loop and so this is a diode and if we put all of this in a big vacuum enclosure well we have our very first vacuum - and it just so happens that I have a couple of vacuum tube diodes that use this same layout that we can maybe experiment and play with a bit so the first diode is the 56:42 vacuum tube diode and if we pull out the datasheet here we can see that there's a whole lot of information going on here but if we look at the second page we can see that the layout of the diode is well it's pretty much exactly what we drew we have our filament down here and we have our plate up here now the plate is designated with an A and that a means anode but a lot of people refer to it as plate and the plate is a little easier for me to keep track in my head so I tend to use plate but you know they're the same thing and you can see that this is this is laid out pretty much exactly the same way so if we take this and we hook it up to its own separate power supply and then we run off of here with a big positive voltage here and a negative voltage down here or our ground down here we can create a diode you know this is this is our load here in the middle now what's interesting about this is I mean you can see it's called a half wave rectifier and well half wave rectifiers are mainly used for turning AC into DC because you know we allow it to travel one direction but we don't allow it to travel the other way so the sine wave of AC can get cut off so AC kind of comes positive and then negative and then positive and so on but because we have a diode there everything down here can't transmit because the diode is blocking it so now we just have our ground here and our positive up here you get a lot of ripple but that's what capacitors are for now the interesting thing about this particular diode is that it's designed for extremely high voltages so you can see we have our our sine wave input here which is a VN with an RMS of 3.6 Q Holt's good lord that's a lot remember how I said I don't like to hurt myself well 3.6 kilovolts is a great way to hurt yourself really badly we can see that actually the max over here is 10 kilovolts good lord alright so that that's that's that's a lot of voltage we're not gonna play with that mostly because it's dangerous but also because my little DC power supply here has a maximum of about 30 volts so let's see what we can do with just 30 volts on this little 56-42 back into so we'll slide this out of the way and we'll take these and scoot them over here and we'll bring over my breadboard here alright so for now we'll just kind of ignore what's going on on the back half of the breadboard and we'll just take a look at these two tubes here and actually I'm really only using one two and that's because if we look at our data sheet here it gives us a little bit of information about the filament and our filaments looking for 1.25 volts which is pretty low and it needs to be a completely isolated power supply from the main supply that we're using for our primary circuit and so I just decided to use this little double-a battery holder that I have here but doublea's put out 1.5 volts and these two doublea's are connected in series so that's three volts and so by running these in series that creates a one-and-a-half volt drop across each one and one and a half volts is a little higher than the 1.25 volts so we're over volting the filaments a little bit but we're not gonna run it for very long so I think it'll be okay and so we have you know the tube here with the filament set up on 1.25 volts and then I have some LEDs over here to kind of demonstrate how the diode effect is is working and so the way this is set up is that this switch right here feeds into the plate on the top and it can feed an either a positive voltage or ground and then coming out of the filament on the bottom and just like in the diagram that we drew earlier the wire comes off of the filament runs over here and crosses over to these two diodes and then the two diodes go through a resistor into another switch and that little switch allows the diodes and resistors combo to either be connected to positive or to ground now what this has done is that it's allowed me to create a way to visually see if a diode is functioning now LEDs are just diodes and so we'll slide this out of the way here for a second and so essentially what we have set up is that we have you know the filament set up on its own voltage source here that's going to be 1.5 volts and then coming off of the filament so that way and then above the filament we have our plate now each one of these goes into a switch and one of these switches goes to plus 24 volts and that's what will bump that up to and the other one goes to ground and then on this side we have it comes down and then we split and on one side we go through a little LED and on the other side we go through an LED but we go through it in the reverse direction and then these two come together and go through a little resistor to another switch and then that switch is connected to ground as well as 24 volts so if the diode were not functioning if we had 24 volts coming through here pass through here would pass through this LED light that led up go through our current limiting resistor so we don't burn the LED to the ground and then go to ground alright but if we were to switch the switches if we were to pop this switch over to ground and pop this switch over to 24 volts you know pop those like that pop that one like that that 24 volts could theoretically if this diode didn't exist could travel up through this current limiting resistor through this led to illuminate there through here and to ground this way all right now remember electrons travel in the opposite direction of what we think of as conventional current flow so if we have a if we have a positive voltage up here and we have our ground down here we think of current as flowing this way but the electrons are going to be flowing from from our ground towards our positive okay so when this is at 24 volts the current we think of is coming out of here flowing through here flowing through our led into ground but in reality the electrons are coming from our ground passing up this weighing and making their way back up to the 24 volts that's very important because our heater is what emits the electrons alright now if the diode didn't work as we said earlier we could we could flip this 24 volts down here and this LED would illuminate so that's what we have set up here so if we bring this down and the first thing we'll do is that we will flip this little switch right here to turn our heaters on and then we will take our power supply here and we'll connect it up to the poles here like so and like so all right and then we'll turn our power supply on here and well go ahead and just bump the voltage up to about 24 volts that seems to be a voltage that I have good luck with running vacuum tubes that's a pretty low voltage but it seems to work really well for our purposes now the yellow LEDs I have here are essentially the same setup as our two diodes and or essentially as our one diode and our two LEDs over here except that I've eliminated this diode and just run a little jumper wire there so right now you can see that we come in through positive here our positive comes in here goes through our switch through here and to our LEDs here now it travels through this LED through the ten thousand ohm resistor here into the Senate pen out of the right pen into ground now if I flip these pins and opposite directions you'll see that the other LED has lit up and that's because now the positive voltage is coming through here up the center pen through our 10,000 ohm resistor through our LED through into the center pen and then back over the ground here now we should be able to do the same here now you can see that there's Wohlers no LEDs lit up but if I switch these switches this way I you can see that we have an LED lit on that so what's happening is the positive voltage is coming out here out the center pin of our switch up to the plate now that is this area right up here all right coming out of the bottom where our filament is we come over to here through our LEDs through our 10,000 ohm resistor into the center pin of the switch out of that into being negative but if I flip these again well now we're doing the opposite we've got positive voltage coming in this way through our 10,000 ohm resistor through an LED that should be lighting up but isn't and then over to our filament and then our plate at the top here is getting our ground so our diode is actually working here conceive it when we pop this over to ground here and we pop this one over to 24 volts here there's no flow because our diode is completely blocking the flow this way but it allows it to flow if we have 24 volts at the top and this high ground here so our diode our diode is working which is amazing because it's operating at just 24 and a half volts and we can actually just drop that down to 24 volts even it yeah it seems to work just fine with no problems there so that's amazing so this this diode does as we pointed out was designed for on the order of kilovolts and yet it seems to be working just fine here now what's going along with this back half here this is a diode but well you can see it's dramatically different looking and these diodes up here and that's because this diode is actually constructed a little different length news and to to understand what's going on there let's well let's let's take this out of the way and take a look at the paper here again so we'll just turn our power supply off pop our power cables out here turn off our our little filaments today I'm gonna go ahead and just slide this thing out of the way now with our previous setup you can see we had a isolated power supply for the filament all by itself and then the filament and the plate were the only two elements inside of the tube now this tube is a little different this is actually a 6a l5 and you can see well you can see right off the bat this layout here is it's very different looking mmm we can also see that our heater voltage our filament voltage is quite a bit higher you can see that you know the 6a l5 has a heater voltage of point three volts so what's exactly is going on here there's a lot more busyness going on in the middle here as well well when they were developing vacuum tubes they kind of discovered that using a directly heated cathode on the bottom which is what our filament was acting it's using a directly heated cathode was not very efficient so they found that they could really bump up efficiency if they used in indirectly heated cathode so you have your your filament coming in like this and then above the filament you have your cathode now the filament gets really hot and it heats up this cathode and this cathode plate gets so hot that it starts to throw off electrons just like before but it's indirectly heated so that makes life a little easier and then of course up top just like before we have our plate that would put a positive voltage on this plate and you know we can run our cathode down here and hook that up to our ground and we have the exact same effect as before we have our exact same diode except that it's now indirectly heated and well we can now create a power source that shares the ground all right so we can we can actually just hook you up to there and then have you come over to you know plus six volts and this makes it a little easier to design the power supply and and other things so you'll notice that in my setup here I'm not actually running a completely isolated power supply I have a little converter that will drop the voltage to six point three volts from 24 volts to make to heat the filament without exploding it but we can pretty much just hook the filament ground up to our regular power supply ground and it doesn't really cause a problem as long as we have a dedicated 6.3 volts coming in all right and so this little tube that we have on there is a you know as we said the six a l5 and you can see that in our little diagram here we have we have our heater down here at the bottom and then we have actually two cathodes and two plates so this is a twin diode there's two diodes inside of of this single tube and that makes it really good for you know rectum rectifying AC and DC as well but also these operate on much lower voltages that's all relative to the previous diodes that we were using I mean you can still see that the the peak inverse plate voltage that's you know going in the opposite direction is 330 volts and the AC plate supply voltage per plate it's about 117 RMS so this this vacuum tube is expecting you know to deal with AC mains AC power so that 120 volts that's coming out of the wall that's that's what this is designed to rectify and deal with but that's still a lot higher than what my little DC power supply is capable of but the other ones worked and they were expecting on the order of kilovolts so let's let's see if this little 6a l5 will work as well now I'm only using half of the diode itself there's there's twin diodes I'm only using one in this in this example so you can see here that that pin 3 and pin 4 our heater you know I have that running out the back here and that runs into my little converter here that's going to drop the 24 volts that's on this rail down to 6 volts for the heater and then you know we should we share the negatives with everything and then just just like before we have it set up so the the plate is you know we can see the plate here is going to be pen 7 and then the cathode that equates to that plate is going to be pin 1 so we're you know we're using the the extreme edges of this 7 pen so pen 7 is going to be all the way over here on the right and then pin 1 is going to all the way over here on the left and just like before we've got positive and round coming into our little switch we got positive and ground coming into our little switch over here and the LEDs are set up exactly the same so theoretically if the diode wasn't functioning we should get one LED lit up in one direction and the other LED lit up in the other direction but if the diode is functioning correctly we'll only get one LED lighting up so let's let's go ahead and hook this up and see what happens we're positive up there we'll hook our are negative up there we'll go ahead and turn our power supply on the the heater is starting to warm up now in the current arrangement that we have set up remember pin 7 is the plate and right now our our switch is set over to hook the plate up to negative this switch is set up to hook the LEDs to positive and while the LEDs are not illuminating because well we're trying to flow in the wrong direction through the diode so if I flip this de positive and I flip this to negative oh hey there we go we got an LED lit up alright check that out so what we have is we have positive coming in to this switch out of that switch into the plate and then we have the cathode on the bottom coming out going through our LEDs through our 10,000 ohm resistor and over to our ground over here so there we go you can see that you know just at a little under 24 volts there we have a diode that is well diving it's doing what it's supposed to do it's preventing flow in one direction and allowing flow in another direction and well that's that's the basics behind vacuum tubes now these are just diodes and dye is indicative of how many elements are inside there which is just you know two elements essentially we have our our cathode and our plate but there's a lot more vacuum tubes and they have a lot more purposes and uses than just diodes and next time we'll take a look at that next time we'll get into the triode and kind of see what they do with that and how those right

Channel: Usagi Electric

Views: 121,080

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Id: rY-a6UUhvhY

Length: 28min 39sec (1719 seconds)

Published: Sun Jun 28 2020