Let's design an build a vacuum tube amplifier from scratch

a blank piece of paper well that can't be any good can it hey what's happening guys today we're gonna start to design our own vacuum tube amplifier I'm designing a frieze as an instrument amplifier with an electric guitar but you could also use it as a hi-fi amplifier yeah same principles exactly it's going to be a very simple amplifier it's going to have one preamp tube which has two stages and a power amp tube so today we're going to talk about designing the signal chain and it's relatively simple it's gonna look something like this well let's put so we're going to have our input and our input is going to go into stage one preamp and then it is going to feed into let's go triangle for volume our volume control which will then feed into stage two of the preamp which will feed into the power amp which will feed into the output transformer which will in turn power the speaker so there's a simple block diagram oh yes also there will be a power supply which will go to all this but today we're only going to be talking about the signal path let's go over the computer and draw some schematics alright let's get started and the first thing that we need to look at here is going to be our preamp and that is the 12ax7 we have two sides of it so imagine drawing the line right there where it says pin 9 is right straight up the middle so you basically have to try ode type vacuum tube amplifiers here so here is our plate which is another word for the anode this is the grid this is the cathode and this down here is the heater filament alright so over here we have our standard quarter inch input jack so we're going to need nope not a passer but a resistor put in between them and we're going to use 68k which is what fender used on all their early tweeds and then that connects to there and we connect that to the screen so that is the input well let's work around on there just so everybody knows what we're talking aboot for those of you on Canadia there we go see a plug your jack into here this is the tip this is the sleeve the tip goes through this resistor here which is known as your grid stop a resistor because it is going right here to our grid okay then we have our cathode and this is where the electrons are going to fly off of so we're going to take another resistor and then this resistors just called our cathode resistor and we're gonna bring it down here like this if for the cathode resist force me is 1.5 K and it also goes to ground so that resistor will prevent the cathode from running away and then we're going to use a bypass on it as well and that is going to be a capacitor in parallel to it and the passer we're going to use is a 25 micro farad at 25 volts like I said that is going to run in parallel now we also have to deal with our plate on this side and that's where the B+ or the high voltage comes from and it is also where our signal is going to feed out okay so we're going to come over here what's been a move over a little bit and we're going to use another coupling capacitor coming out of here and this is going to be a point O 2 micro farad at 600 volt this is your high voltage capacitor you need to have that then that's going to come over here and go to our plate and if we wanted to what we will we'll add in our plate voltage over here okay so now we've come out of here this is our signal coming out of the plate and we need to feed it back into the grid on this side but this is where we are going to add in the volume and the volume is a one MIG potentiometer just like that and it also flows the ground here we rotate that there we go and that is going to feed in to the grid over here and then when we take our cathode again we're going to do the same thing we did down here so we're going to put in another resistor same thing for this cathode this is also 1.5 K and it flows the ground to our catheter and I'm just going to copy this guy was to come in there like that and that's our bypass on that cathode as well so now we take our signal out of this plate which has been amplified so we have our very low signal coming in from the guitar goes through our grid stopper resistor and into the grid of the first side of our preamp it regulates how many electrons flow from the cathode to the plate they come out of the plate through this coupling capacitor into our potentiometer and into the second side are you with me so far good so now we're going to flow out of there to our main power amplifier which in this case is going to be a six v6 tube okay so as you can see I just throw a 6v6 tube on here and now we're going to need another one of these coupling caps here which is going to go over here to that grid so we're going to come out of here yeah oops don't like that like this good that's better so now we have our completely amplify signals been amplified twice here in the preamp and it now comes over and starts to feed the power amp and again we are going to need a resistor for its cathode and in this case we're going to use a 470 ohm resistor and of course we are going to bypass it as well here and it will also float notice how everything goes to ground okay so now that that is all put together we then have our signal coming out of here this is the the plate here our signal is going to come out of the plate and it is going to go through our output transformer so that is the next thing we need all right so I've just put a little transformer here now we are going to come out of here and there'll be no coupling this time and we go directly into our output transformer and then the other side of our output transformer is going to go to our beat Plus which is our power supply part of the circuit which we haven't tackled yet now these two here a part of the screen and they will also go to our power supply we haven't tackled them yet either so now we need to put in a speaker which is going to attach over here as such our speaker attaches to the backside of our output transformer and basically you can now see the signal path through here except for one little thing which is if we wanted to use a feedback resistor negative feedback and you could get our negative feedback by tapping into this point right here and feeding back to this point over here on the cathode side of this the second side of our preamp of the 12ax7 I don't know if I'm gonna add that in or not what do you guys think should I put negative feedback in here or not I don't know all right so we're gonna cap it here for this this is the intro to art amplifier vacuum tube amplifier design and just to say you don't have to put a speaker or a guitar plug here put a cut you can put RCA plugs here and you know make this a hi-fi amplifier as well in the next part we will look at adding in the power supply to this which will finish out all of our unused connections alright alright before we finish up just a really quick primer on tubes in case you're not familiar with them this is the anode or what's called the plate this is this is my computer starting up this is the cathode and this is the grid you apply your high voltage to the plate in this type of amp you ground up the grid this is just these are your filament wires they just heat up the tube to make it work properly and your signal goes into the grid so what's happening is electrons are jumping off the heat cathode and attracted to the positively charged anode and by controlling the grid which is a lot like a chain-link fence where you can vary the width of the links we can control how many electrodes are allowed to jump through and then we take our signal off of that point there hope that helps all right that's it for today like I said the next part we are going to put together the power supply for our amplifier thank you for watching I hope you're keeping safe feels please feel free to like share comment subscribe wash your hands don't touch your face that's it I'm out peace I want to thank you all for watching and spending time with me today the 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Channel: learnelectronics

Views: 154,905

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Id: 9AABLml-ERE

Length: 16min 10sec (970 seconds)

Published: Fri Apr 17 2020