Thanks for sharing, I am also a service engineer was based in Harrow, then Milton Keynes, worked for Roland, Yamaha Line 6 and Alesis (mostly digital with some transistor circuits, since relocating to Brazil, I am called to repair guitar valve amps and authorised by Marshall, Fender, Bugera etc. I only have just over 35 years of experience but not a huge amount on valves. Thanks to your channel and Uncle Dougs, I have refined my knowledge and also learnt about substitution of tubes and their characteristics (ie. EL34, 6L6, 6V6..). You'll be glad to know I already knew 99% of what you said, but it's good to be reminded and I wasn't too sure on how the negative bias was derived. Unfortunately many amps don't have a bias pot, so you need to calculate the relevant resistors.
Stuart, I completed my first cap job on my Fender Concert today. I also replaced several resistors that were out of spec. I plugged it in with my variac and bulb set up. It no longer blows fuses, but I found the vibrato channel was still weak. I couldn't figure this out until I pulled the tube and one of the connectors came off on the tube. It must have been broken. I will replace this socket and see if that clears it up. It is your videos that Gave me confidence to do this and the ability to do it in a safe manner. The video on schematics has helped me greatly in understanding how tube amps work. I'll continue watching and learning while exercising my skills. Thank you so much for your continued tutoring. Mike.
It's me again ! hihi ! I'm a house builder and so frustrated that I didn't choose electronics when I was youger at school . Trying to understand and re-visiting this video and I must say that the way you explain things is really good so thanks for the second time ! Will watch them all and like them all !
Hi lou. I'm an electronics engineer and so frustrated I didn't become a builder5 - would have been minted by now!! :) I'm glad you're enjoyong the vids. Keep learning!
Extremely helpful!! I just purchased a Fender Bandmaster head Non-functioning, which is my first amp to try and fix. This AB763 is the exact same circuit in that amp also. Thank you for this!!
A useful automotive-themed mnemonic device for understanding the symbols for resistors and capacitors is that a resistor is like a series of speed bumps for forcing traffic (voltage and current, ie: electrons) to slow down and lose energy; and a capacitor is like an automated tollbooth gate mechanism that needs to be charged up (a handful of coins thrown in the basket) before it can let the current pass through.
Thank you so much! I will watch this many times I'm sure. I'm amazed at how much this opens my understanding and brings new questions at the same time.
I watch and listen to this before any DIY on my amplifiers, it helps keep my mind clear of clutter and gives me a bit of "Why" these components work, thankyou.
I am building up courage and confidence to "repair" my super twin reverb" also i have a twin reverb with several known issues . In my search in the last year this video is the most valuable in understanding how amps work. Thank you a bucket of tone for your generosity in educating people! Cheers!🎉
Hello Stuart, I'm a Japanese guy who builds his own guitar amps as a hobby. I found it helpful to remove the thin wire coating inside the reverb tank by melting it with the tip of a soldering iron. I don't want to put tension on the thin lines, so I'll try it next time.
I’m currently building a deluxe reverb with this AB763 circuit i have absolutely no idea about any of it but it was brilliant to learn a little and i am sure i will come back agin and again until it all syncs in properly so thank you very much indeed
Hello Stuart, great tutorial.... I changed my normal circuit on my Vibrolux reverb amp. I changed the .047uf coupling capcitor to a .033uf and changed the tone stack bass .047 uf cap to a .022uf like the super reverbs. I now enjoy the normal channel. It seems more open and not muddy . Very useful.
Found this really useful! I would find another walk through like this with a class A solid state amp really helpful as well. The way you explained everything was at the perfect level of specificity.
Fan-Flippin'-tastic! Solid Value in this video. I did pick up a little bit more with your video and I got reinforcement on what I learned before but maybe kind of forgot. Thank you Mr. Stuart. Much obliged.
Thanks for the great tutorial. You have a real gift for making all the seemingly complicated very easy to understand for the novice, without unnecessary waffle or condescension. It's much appreciated. I've subscribed and I look forward to diving into more of your videos. I'd really love if you could do the same breakdown with some guitar pedals. Cheers.
Very well done cleared up a lot of questions ....I have worked on my own and some friends' amps for years and schematics are a weak point. I have been doing a deep dive on them for a few months now and this was very helpful. Thanks and Regards
Hi Stuart. I've owned a few amps over the years (from a 200w Marshall stack back in the 70's to a Vox 2w [two w] Night Train now!) but never really understood what goes on under the bonnet. Your videos are fascinating and very easy to understand because of your style of presentation. Thank you.
@@stuartukguitarampguy5830 Probably closer to 100mW. Nevertheless with a good sensitive speaker and a decent enclosure it was loud enough to make my neighbors angry 🙂😠
I've had been interested pretty recently into electronics, specifically for amp construction and studying more deeply a Mesa/Boogie Mark IIC+ schematic. Stuart, I can't thank you enough for this video as it's shedding a light on what it seemed like pretty much rocket science so far as a newcomer 😂
Excellent presentation Stuart. Really enjoy your videos. Would be a blast hanging out with you in your shop for a few days. Thanks for sharing your knowledge. Looking forward to watching some more of your videos.
Would love to see you go through each half of the 12ax7's and what they do, cathode follower vs driver stage vs phase inverter(long tail vs cathodyne) ect. Thank you
Hey Stuart, just a fab video..Lots learned again...This explanation of the circuit certainly does remove some of the fog I have with regard to the schematic and it's reading. Thanks again for posting, keep em' coming..Ed..UK..😁
Thanks mate, that was really informative and well explained. I built a couple of 5E3 Fender Deluxe clones that wen really well and enjoyed the build. It's good to have an understanding of how things work. Cheers !!
Great video Stuart especially showing the part of the amp's actual circuit relating to the schematic. It certainly helps if you can read resistor values which helps you identify from the diagram which part of the amps circuit your looking at or trying to identify.
Thank you so much for all your videos Stuart! You have really helped me learn a lot. Your channel is worth its weight good (and I'd venture your channel has featured quite a few ac30s, so that's a lot!)
Thank you for the spot on amount of information here. I matched the rest of the schematic to the components .. I think 🙂. The 3 CAPS in the POWER amp, and the 2 series caps of the Power supply are in the "doghouse", is this correct? By showing us the Vibrato Preamp section, it was easy to deduce the pre-amp for Normal and Reverb (on a SuperReverb). Awesome, thanks again!
I really enjoy your videos. I am an "automotive technician," so I get the diagnostic process. Have you made a video of th ahop, or more specifically, your special and not so special tools? I have been able to pick up on a few watching your videos. Thanks for doing what you do . P.S. im especially interested in your magnified and lighted work glasses.
Not sure if you're still responding to this video. First, thank you for the video. I have some formal education ( 20 years ago) but no real world experience. For some reason I have become interested in tubes. I have watched several videos on guitar amps with tubes. One thing I can't wrap my mind around is how the plate voltage for the final power valve (6L6GC) is fed through the output transformer. The same transformer for the output to the speakers. It seems this would create noise problems for one. It seems the plate would be fed directly the 440 volts and the transformer would be fed the signal possibly through a cap to remove any dc voltage. Its hard to state the question accurately with no practical experience. Hopefully you understand the question. Thanks in advance for any response.
Hi Gary. I wonder why you think it would cause noise? Think of the output transformer primary as being the ''load resistor' for the output valve. That might help. The valve pulls and pushes current backwards and forwards through the primary winding. This is coupled magnetically to the secondary which is connected to the speaker. Think of a simple version. You have a primary, one side connected to the +ve of a battery, the other side connected to a push switch to ground. When you push the switch, the coil is energised, current flows through it, a magentic field is created, this 'cuts' the turns of the secondary. If the seconday is connected to a speaker, you'd hear a POP each time you pressed the button. The valve setup is just a bit more sophisticated than this.Does that help?
Excellent. As a mechanical engineer (!) But some (30 year old) electrical training, this is really interesting to understand whats happening in my valve amp. 1 question - whats the purpose of the 220k resistor after the pre-amp stage (after the coupling capacitor) ? In my simplistic head, doesn't that just lose some of the hard-earned increase in power just made in the pre-amp ?
Hi Mr. Stuart, your beginner tutorials are amazing. I have learned more about electronics and power circuits from your 3 videos about how tube amplifiers work than in all the hours of classes in school and university. I am a bit ashamed to say it frankly, but the truth is that mechanical engineer degrees in my country don’t go very deep into electro-engineering. Is there a possiblity that you make similar videos for transistor amplifiers like the ones you made for tube amplifiers? Cheers.
Thanks very much! It's the same for me. My degree in electrical engineering didn;t really do much on the mechanical side. Yes that's a good idea, I'll do one on transistor schematics.
Fantastic video. Thanks so much. It would be cool if you could explain in the input jack the low impedance and the high impedance inputs. Also, when we see connections to ground, is it really the amp ground or is the ground connected to the Neutral power supply cable?
@@stuartukguitarampguy5830 Hi, thanks for your reply. Is it normal to have circuit that just dumps a massive amount of current to the ground as part of normal operation? The giant smoothing capacitors with the 400 volts rating in series, are acting like some sort of high pass filter right? The AC signal starts becoming like DC to feed the voltage of the power tubes but the high frequencies are constantly sent to ground. I suppose this is normal, but still somewhat surprising as sending signal to ground is normally we intuitively see happening as a safety mechanism when something shorts and connects a voltage source to the metal casing. Still too much of a ignorant in respect to electrical circuits, it's what it is.
@@ertreriHi It's a bit hard to explain in short reply. Maybe the mest way is to consider a battery connect to a lamp. So the positive goes to one side of the lamp and the negative to another. The amp lights. WHere is the current from the positive terminal (which goes through the lamp) being 'dumped' to? It's dumped to the negative side of the battery, right? Now if I happen to also want to connect that negative terminal to my metal case and also the mains ground, nothing changes. No current is being 'dumped' to ground in that case. It's the same with mains powered gear. That's the best I can do without a coirse in electrics! Keep studying and learning.
Really great explanation! Would you be willing to make a video how guitar schematics map to the actual circuit boards? That's what I conceptually don't understand because the board obviously looks nothing like the schematics, even though it follows it (I guess) :D
Hi. The problem with that is that it varies from amp to amp, there is no standard tranlation. It's not usually too difficult to follow though. E.g. find V1, then find pin 2, ah... there's the 100k resistor which is on the schematic etc. The layout is usually fairly logical.
Good presentation Stuart! If you want to give yourself a headache, track down a schematic for a Fender Super Twin Reverb amp. They were only produced from about 1976 thru 1980 or so. 180Watts RMS, 395 Watts Peak. Six 6L6CG power tubes, and a couple of unusual tubes in the circuit. (6C10 and 6CX8). If you want to see photos of the inside of mine, let me know.
@@stuartukguitarampguy5830 Hello Stuart. I have that schematic. I actually printed it out on four letter sized pieces of paper and taped them together. I showed "Uncle Doug" how to set up the printer to accomplish that. It comes in handy for complicated schematics where you want a hard copy to make notes on.
@@miguelrichartmellado2834 Yes, 2 x 12 combo. Mine has the UTAH speakers with the large square magnets. Very heavy. I built a head cabinet for the chassis, and left the speakers in the original cabinet so it's easier to transport.
In this video, the guitar input circuit looks interesting. The input signal seems to be going through resistors to the preamp grid, but there's also a path for both inputs 1 and 2 that appears to be grounded. Is this intentional, or are the ground wires supposed to connect to the jack's ground lug instead of the hot connection? it is hard to imagine a short to ground from the hot would make any sense. thanks
I think what you're seeing is the fact that when the guitar lead is UNPLUGGED, the hot contact is grounded. This is to stop the amp humming. When you plug in, this ground connection is broken.
@@stuartukguitarampguy5830 Thanks, that was most definitely not obvious. While a direct short to ground on the hot input during normal operation wouldn't necessarily damage the circuit, it's not a typical design choice for a couple of reasons: 1. **Potential for Ground Loops:** Even though the hot isn't connected to a power source until the guitar cable is plugged in, a direct short to ground on the input could create a ground loop if there are other grounding inconsistencies in the circuit. Ground loops can introduce unwanted hum or noise. 2. **Unexpected Behavior During Troubleshooting:** If a technician were troubleshooting the amp without a guitar plugged in, a direct short to ground on the hot could lead to unexpected behavior, making it more difficult to diagnose the actual problem. In a well-designed amp, grounding the sleeve of the input jack is the preferred method to minimize noise when no cable is plugged in. This avoids potential ground loops and unexpected behavior during troubleshooting. Would you agree?
On the high tension rectifier, are there three diodes stacked in series to allow for a lower voltage rated diode to be used to withstand the 440V B+? ( Im thinking along the lines of three 250v diodes could withstand 750v in series...)
Hello, great vid, I am looking for the best place to get a schematic for Peavey valveking 112 version one, that shows the valve positions V1, 2 and 3 so I can experiment/try different pre amp tubes, any pointers would be appreciated.
V1,2,3 are all 12AX7 (ECC83). LEave V3, that's the one nearest the power tubes and is the phase inverter. V1 is nearest the input jack. There's not a lot you can experiment with really. You won't hear any difference between valve makes. All you can do is reduce the gain but putting a 12AY7 in the V1 position. What are you trying to achieve?
@@stuartukguitarampguy5830 Thanks very much for replying Stuart, I was after exactly what you said, I have a HRDLX I got an amp tech to swop out the original Caps, I put a ecc81/12AT7 in V1 and changed the speaker for a TREX and bingo, sounds great i'm into SRV. I can find schematics for the fender but nothing decent for the valveking, so I wanted to know which was V1, you answered that and I am very greatfull, what do you think of the 12AT7 in V1 on the Peavey ?
@@ronnocm8633 I have the schematic for the VK if you want it. At the end of any video you'll see an end graphic with my email on it, contact me via that. I prefer an 12AY7 to the ECC81 if it's a gain reduction you are looking for.
STUART, What are grid leakage and grid stopper resistors used for? the grid leakage is leaking the AC peak to peak voltage to ground which I'm guessing the term leakage means a voltage drop? and the grid stopper is stopping what? the AC peak to peak voltage from going into the tubes grid. The terms Stopper and Leakage I'm confused about why they are calling them stoppers and leakage and what they mean by them
Hi Wayne. These are archaic terms and not very helpful really! The 'grid stopper' is in series wih the grid. The grid has a capacitance to ground, so with this resistor you have a low pass filter. 'Low Pass' means 'High Rejection' - so it's rejecting (attenuating) high frequencies such as radio frequencies. Without this that amp would becoame a passable radio receiver. Think of it maybe as STOPPING the high frequencies. The 'grid leakage' resistor is conected from the grid to ground. It provides bias for that valve (basically without it there's no path to ground from the grid - it would be 'floating'. ) A downside of this resistor is that it attenuates the signal from the previous stage and hence reduces its level. I hope that helps.
@stuartukguitarampguy5830 thanks for the help and information. I was confused why they call those resistors grid stop and grid leakage. I get what your wrote it helps out
@@stuartukguitarampguy5830 I think the Tubes Grid is "leaking" positive DC voltage that is why you need to connect a "pull down/leakage" Resistor to pull down the grid leakage voltage to ground 0 volts. If no Grid leakage resistor the grid is Floating which can cause oscillations, unstable issues, noises.
@@waynegram8907 That's true but it's not the best way to look at it. A better way is just to say that the grid needs a bias voltage on it so that the cathode can be negative with respect to it. The bias voltage in this case is 0V and the grid resistor ensures this.
@@stuartukguitarampguy5830 What do you mean by the Cathode can be negative with respect to the grid at 0 volts? The Cathode would have to be BELOW 0 Volts -10vdc to -30vdc?
@@stuartukguitarampguy5830 peavey amp.. my first real badass amp I got around 2001 and it just died... dont know why... not places around me that fixes them... had a guy looking at it... he does some stuff with amps... its got him stumped... I have another one, but thats my baby...
When a newcomer to all this, this is exactly the content you need. Very instructional and thank you Stuart
Thanks Howard
Thanks for sharing, I am also a service engineer was based in Harrow, then Milton Keynes, worked for Roland, Yamaha Line 6 and Alesis (mostly digital with some transistor circuits, since relocating to Brazil, I am called to repair guitar valve amps and authorised by Marshall, Fender, Bugera etc. I only have just over 35 years of experience but not a huge amount on valves. Thanks to your channel and Uncle Dougs, I have refined my knowledge and also learnt about substitution of tubes and their characteristics (ie. EL34, 6L6, 6V6..). You'll be glad to know I already knew 99% of what you said, but it's good to be reminded and I wasn't too sure on how the negative bias was derived. Unfortunately many amps don't have a bias pot, so you need to calculate the relevant resistors.
Great to hear from you and thanks for shating. I went to Recife once!
As a guitar player I really enjoy you walking us through these amps
Thanks Mario!
@stuartukguitarampguy5830 wow...your so smart...and the way you explain is so good..
Stuart,
I completed my first cap job on my Fender Concert today. I also replaced several resistors that were out of spec. I plugged it in with my variac and bulb set up. It no longer blows fuses, but I found the vibrato channel was still weak. I couldn't figure this out until I pulled the tube and one of the connectors came off on the tube. It must have been broken. I will replace this socket and see if that clears it up. It is your videos that Gave me confidence to do this and the ability to do it in a safe manner. The video on schematics has helped me greatly in understanding how tube amps work. I'll continue watching and learning while exercising my skills. Thank you so much for your continued tutoring.
Mike.
Excellent well done Michael.
It's me again ! hihi ! I'm a house builder and so frustrated that I didn't choose electronics when I was youger at school .
Trying to understand and re-visiting this video and I must say that the way you explain things is really good so thanks for the second time !
Will watch them all and like them all !
Hi lou. I'm an electronics engineer and so frustrated I didn't become a builder5 - would have been minted by now!! :) I'm glad you're enjoyong the vids. Keep learning!
@@stuartukguitarampguy5830 Haha ! That is funny ! I love the vids ! Take care !
36:41 The choke and the first 20u/525V capacitor form an LC filter, applying a stage of smoothing to the DC supply to the screen.
Extremely helpful!! I just purchased a Fender Bandmaster head Non-functioning, which is my first amp to try and fix. This AB763 is the exact same circuit in that amp also. Thank you for this!!
A useful automotive-themed mnemonic device for understanding the symbols for resistors and capacitors is that a resistor is like a series of speed bumps for forcing traffic (voltage and current, ie: electrons) to slow down and lose energy; and a capacitor is like an automated tollbooth gate mechanism that needs to be charged up (a handful of coins thrown in the basket) before it can let the current pass through.
Nice thanks.
Thanks for sharing. Sat there glued to every word and learned a lot 👍
Thanks very much.
Thank you so much! I will watch this many times I'm sure. I'm amazed at how much this opens my understanding and brings new questions at the same time.
Thanks Michael I'm pleased you found it useful.
I watch and listen to this before any DIY on my amplifiers, it helps keep my mind clear of clutter and gives me a bit of "Why" these components work, thankyou.
Thanks Giulio I'm glad you find it useful.
As a novice - this is explanation has been invaluable. Thank you for taking the time to do this. Areal gentleman and scholar.
Thanks very much.
I am building up courage and confidence to "repair" my super twin reverb" also i have a twin reverb with several known issues .
In my search in the last year this video is the most valuable in understanding how amps work.
Thank you a bucket of tone for your generosity in educating people!
Cheers!🎉
Thanks and good luck fixing it.
Hello Stuart, I'm a Japanese guy who builds his own guitar amps as a hobby.
I found it helpful to remove the thin wire coating inside the reverb tank by melting it with the tip of a soldering iron. I don't want to put tension on the thin lines, so I'll try it next time.
Yes that's the best method.
I’m currently building a deluxe reverb with this AB763 circuit i have absolutely no idea about any of it but it was brilliant to learn a little and i am sure i will come back agin and again until it all syncs in properly so thank you very much indeed
Great I'm pleased it was useful and good luck with the project!
This was great, and even having watched a great many “basics” videos, you clarified several points for me. Thank you!
Excellent thanks Stephen
Excellent primer; thank-you. Looking forward to more. Topics of interest: a) amp biasing demonstration, b) Class D amp schematic primer. Thanks again!
Thanks David. I wonlt be doing the class D primer - barely understand it myself!
Hello Stuart, great tutorial.... I changed my normal circuit on my Vibrolux reverb amp. I changed the .047uf coupling capcitor to a .033uf and changed the tone stack bass .047 uf cap to a .022uf like the super reverbs. I now enjoy the normal channel. It seems more open and not muddy . Very useful.
Ok interesting thanks.
Found this really useful! I would find another walk through like this with a class A solid state amp really helpful as well. The way you explained everything was at the perfect level of specificity.
Thanks for the great feedback I'm glad you enjoyed the vid.
Fan-Flippin'-tastic! Solid Value in this video. I did pick up a little bit more with your video and I got reinforcement on what I learned before but maybe kind of forgot.
Thank you Mr. Stuart. Much obliged.
Excellent!
Thanks for the great tutorial. You have a real gift for making all the seemingly complicated very easy to understand for the novice, without unnecessary waffle or condescension. It's much appreciated.
I've subscribed and I look forward to diving into more of your videos. I'd really love if you could do the same breakdown with some guitar pedals. Cheers.
Thanks James. Hmm, guitar pedals are SO varied and often fiendishly complicated. They even have 100 pin computer chips and suchlike in them!
Very well done cleared up a lot of questions ....I have worked on my own and some friends' amps for years and schematics are a weak point. I have been doing a deep dive on them for a few months now and this was very helpful. Thanks and Regards
Great I'm glad it was helpful!
Hi Stuart. I've owned a few amps over the years (from a 200w Marshall stack back in the 70's to a Vox 2w [two w] Night Train now!) but never really understood what goes on under the bonnet. Your videos are fascinating and very easy to understand because of your style of presentation. Thank you.
Thanks Brendan
Stuart, you rock more than all the amps you've ever serviced combined. Thank you for taking the time to make this video.
You're too kind!
I had a home-made amplifier in the 70's using a single 12AX7 in class-A ouput stage. It was good enough for me.
Ooo, nice, About half a watt then!
@@stuartukguitarampguy5830 Probably closer to 100mW. Nevertheless with a good sensitive speaker and a decent enclosure it was loud enough to make my neighbors angry 🙂😠
Thank you for taking the time too share the knowledge , my kind of entertainment for sure.
From across the pond ,thumbs up!
Cheers Ronnie
Fabulous, exactly the videos I want to see and learn from cheers
Cheers Richard
I've had been interested pretty recently into electronics, specifically for amp construction and studying more deeply a Mesa/Boogie Mark IIC+ schematic. Stuart, I can't thank you enough for this video as it's shedding a light on what it seemed like pretty much rocket science so far as a newcomer 😂
Great I'm pleased you liked it.
Excellent presentation Stuart. Really enjoy your videos. Would be a blast hanging out with you in your shop for a few days. Thanks for sharing your knowledge. Looking forward to watching some more of your videos.
Thanks I'm pleased you enjoyed it! Feel free to drop in if you are down my way (Reading)
Thank you very much for this! Learnt so much from you already and excited to get stuck into some less beginner friendly content soon!
Excellent thanks Kit
Would love to see you go through each half of the 12ax7's and what they do, cathode follower vs driver stage vs phase inverter(long tail vs cathodyne) ect. Thank you
Awesome explanation.. iv done an electronics degree but never did valve amps .. loved this thanks
Thanks Peter.
Very very good video. Thank you Master.
Thanks Miguel.
This was very illuminating! Many thanks!
I'm pleased you found it useful.
Hey Stuart, just a fab video..Lots learned again...This explanation of the circuit certainly does remove some of the fog I have with regard to the schematic and it's reading. Thanks again for posting, keep em' coming..Ed..UK..😁
Thanks Ed
you have no idea how helpful this was. thanks!!
Thank you so much!
Thanks mate, that was really informative and well explained. I built a couple of 5E3 Fender Deluxe clones that wen really well and enjoyed the build. It's good to have an understanding of how things work. Cheers !!
Great well done Adam
Amazingly informative again Stuart! Thanks!
Thanks! Glad you enjoyed it.
Really useful video - thanks for sharing your extensive knowledge.
Thanks Greg
Great video Stuart especially showing the part of the amp's actual circuit relating to the schematic. It certainly helps if you can read resistor values which helps you identify from the diagram which part of the amps circuit your looking at or trying to identify.
Cheers Pete
Very informative for beginners. It's nice that you take your time to teach here 👏
Thanks Richard
Thank you so much for taking the time to explain this.
I'm pleased you liked it.
hi Stuart.. Thanks for the basics very much appreciated Top man ..
I'm pleased you enjoyed it.
Very cool. Trying to follow along on my Marshall JMO schematic. Fender definitely is easier to follow.
Great that's how you learn!
Absolutely fantastic video, thank you so so much!
Thanks Tomas!
Thank you so much for all your videos Stuart! You have really helped me learn a lot. Your channel is worth its weight good (and I'd venture your channel has featured quite a few ac30s, so that's a lot!)
Thanks I'm really pleased you enjoy it!
Thank you for the spot on amount of information here. I matched the rest of the schematic to the components .. I think 🙂. The 3 CAPS in the POWER amp, and the 2 series caps of the Power supply are in the "doghouse", is this correct? By showing us the Vibrato Preamp section, it was easy to deduce the pre-amp for Normal and Reverb (on a SuperReverb). Awesome, thanks again!
Yes that's correct. Glad you enjoyed it!
I really enjoy your videos. I am an "automotive technician," so I get the diagnostic process.
Have you made a video of th ahop, or more specifically, your special and not so special tools? I have been able to pick up on a few watching your videos.
Thanks for doing what you do .
P.S. im especially interested in your magnified and lighted work glasses.
Hi David I'm pleased you are enjoying the vids! No I haven;t made any vids on the tools I use apart from the variac setup I have.
What a brilliant video. Thank you!
Thanks John
Keep up the great work 👍🏻👌🏻
Not sure if you're still responding to this video. First, thank you for the video. I have some formal education ( 20 years ago) but no real world experience. For some reason I have become interested in tubes. I have watched several videos on guitar amps with tubes.
One thing I can't wrap my mind around is how the plate voltage for the final power valve (6L6GC) is fed through the output transformer. The same transformer for the output to the speakers. It seems this would create noise problems for one. It seems the plate would be fed directly the 440 volts and the transformer would be fed the signal possibly through a cap to remove any dc voltage. Its hard to state the question accurately with no practical experience. Hopefully you understand the question. Thanks in advance for any response.
Hi Gary. I wonder why you think it would cause noise? Think of the output transformer primary as being the ''load resistor' for the output valve. That might help.
The valve pulls and pushes current backwards and forwards through the primary winding. This is coupled magnetically to the secondary which is connected to the speaker.
Think of a simple version. You have a primary, one side connected to the +ve of a battery, the other side connected to a push switch to ground. When you push the switch, the coil is energised, current flows through it, a magentic field is created, this 'cuts' the turns of the secondary. If the seconday is connected to a speaker, you'd hear a POP each time you pressed the button. The valve setup is just a bit more sophisticated than this.Does that help?
I worked in civil engineering for 30yrs I'm hoping this will be similar enough tht it will be a smooth transition. I'll see soon enough . Thks
Let's hope so!
Can you explain what B+1,B+2,B+n stands for? Thanks for the excellent lesson!
They're just old deginations from way back when. Mught as well call the A, B and C for want of anything better. They are DC voltages.
Excellent. As a mechanical engineer (!) But some (30 year old) electrical training, this is really interesting to understand whats happening in my valve amp.
1 question - whats the purpose of the 220k resistor after the pre-amp stage (after the coupling capacitor) ? In my simplistic head, doesn't that just lose some of the hard-earned increase in power just made in the pre-amp ?
Hi those 2 x 220K resistors are where the bias voltage is fed in. They are very high value resistors and so the loss is very small.
Very informative video. Thanks.
I'm pleased you enjoyed it.
Hi Mr. Stuart, your beginner tutorials are amazing. I have learned more about electronics and power circuits from your 3 videos about how tube amplifiers work than in all the hours of classes in school and university. I am a bit ashamed to say it frankly, but the truth is that mechanical engineer degrees in my country don’t go very deep into electro-engineering. Is there a possiblity that you make similar videos for transistor amplifiers like the ones you made for tube amplifiers? Cheers.
Thanks very much! It's the same for me. My degree in electrical engineering didn;t really do much on the mechanical side. Yes that's a good idea, I'll do one on transistor schematics.
Fantastic video. Thanks so much. It would be cool if you could explain in the input jack the low impedance and the high impedance inputs. Also, when we see connections to ground, is it really the amp ground or is the ground connected to the Neutral power supply cable?
Glad you enjoyed it. Yes the ground is the metal chassis and that's connected to the eartn wire in the plug, definitelty not neutral!
@@stuartukguitarampguy5830 Hi, thanks for your reply. Is it normal to have circuit that just dumps a massive amount of current to the ground as part of normal operation? The giant smoothing capacitors with the 400 volts rating in series, are acting like some sort of high pass filter right? The AC signal starts becoming like DC to feed the voltage of the power tubes but the high frequencies are constantly sent to ground. I suppose this is normal, but still somewhat surprising as sending signal to ground is normally we intuitively see happening as a safety mechanism when something shorts and connects a voltage source to the metal casing. Still too much of a ignorant in respect to electrical circuits, it's what it is.
@@ertreriHi It's a bit hard to explain in short reply. Maybe the mest way is to consider a battery connect to a lamp. So the positive goes to one side of the lamp and the negative to another. The amp lights. WHere is the current from the positive terminal (which goes through the lamp) being 'dumped' to? It's dumped to the negative side of the battery, right? Now if I happen to also want to connect that negative terminal to my metal case and also the mains ground, nothing changes. No current is being 'dumped' to ground in that case. It's the same with mains powered gear. That's the best I can do without a coirse in electrics! Keep studying and learning.
Thanks! You explain it well!
Really useful. Thank you!
Really great explanation! Would you be willing to make a video how guitar schematics map to the actual circuit boards? That's what I conceptually don't understand because the board obviously looks nothing like the schematics, even though it follows it (I guess) :D
Hi. The problem with that is that it varies from amp to amp, there is no standard tranlation. It's not usually too difficult to follow though. E.g. find V1, then find pin 2, ah... there's the 100k resistor which is on the schematic etc. The layout is usually fairly logical.
Well done 👍
You’re the best!!🙏🏼
Thanks Jason.
Thank you VERY much! Very informative...to me anyway. I'm a rookie. Subscribed.
Great I'm so pleased.
Good presentation Stuart! If you want to give yourself a headache, track down a schematic for a Fender Super Twin Reverb amp. They were only produced from about 1976 thru 1980 or so. 180Watts RMS, 395 Watts Peak. Six 6L6CG power tubes, and a couple of unusual tubes in the circuit. (6C10 and 6CX8). If you want to see photos of the inside of mine, let me know.
Hi Michael I have that schematic do you need it?
That amp is a monster. In my city there are two, 2x12" combo.
@@stuartukguitarampguy5830 Hello Stuart. I have that schematic. I actually printed it out on four letter sized pieces of paper and taped them together. I showed "Uncle Doug" how to set up the printer to accomplish that. It comes in handy for complicated schematics where you want a hard copy to make notes on.
@@miguelrichartmellado2834 Yes, 2 x 12 combo. Mine has the UTAH speakers with the large square magnets. Very heavy. I built a head cabinet for the chassis, and left the speakers in the original cabinet so it's easier to transport.
@@MichaelSmith-rn1qw Ok great. I usually just print off the bit I'm interested in. Tbh I rarely have to do even that.
Man you are awesome....I subbed.
cheers Josh!
Hi Stuart I also have a schematic of a Preamp by Langner. It is a bit complicated. Maybe you can check it out.
Oh man , how come this one slipped ! So happy ! Thank you Sir !!
Glad you enjoyed it!
In this video, the guitar input circuit looks interesting. The input signal seems to be going through resistors to the preamp grid, but there's also a path for both inputs 1 and 2 that appears to be grounded. Is this intentional, or are the ground wires supposed to connect to the jack's ground lug instead of the hot connection? it is hard to imagine a short to ground from the hot would make any sense. thanks
I think what you're seeing is the fact that when the guitar lead is UNPLUGGED, the hot contact is grounded. This is to stop the amp humming. When you plug in, this ground connection is broken.
@@stuartukguitarampguy5830 Thanks, that was most definitely not obvious.
While a direct short to ground on the hot input during normal operation wouldn't necessarily damage the circuit, it's not a typical design choice for a couple of reasons:
1. **Potential for Ground Loops:** Even though the hot isn't connected to a power source until the guitar cable is plugged in, a direct short to ground on the input could create a ground loop if there are other grounding inconsistencies in the circuit. Ground loops can introduce unwanted hum or noise.
2. **Unexpected Behavior During Troubleshooting:** If a technician were troubleshooting the amp without a guitar plugged in, a direct short to ground on the hot could lead to unexpected behavior, making it more difficult to diagnose the actual problem.
In a well-designed amp, grounding the sleeve of the input jack is the preferred method to minimize noise when no cable is plugged in. This avoids potential ground loops and unexpected behavior during troubleshooting.
Would you agree?
On the high tension rectifier, are there three diodes stacked in series to allow for a lower voltage rated diode to be used to withstand the 440V B+? ( Im thinking along the lines of three 250v diodes could withstand 750v in series...)
Hi Dan Yes I believe that is why they do it.
Thanx for sharing
Hello, great vid, I am looking for the best place to get a schematic for Peavey valveking 112 version one, that shows the valve positions V1, 2 and 3 so I can experiment/try different pre amp tubes, any pointers would be appreciated.
V1,2,3 are all 12AX7 (ECC83). LEave V3, that's the one nearest the power tubes and is the phase inverter. V1 is nearest the input jack. There's not a lot you can experiment with really. You won't hear any difference between valve makes. All you can do is reduce the gain but putting a 12AY7 in the V1 position. What are you trying to achieve?
@@stuartukguitarampguy5830 Thanks very much for replying Stuart, I was after exactly what you said, I have a HRDLX I got an amp tech to swop out the original Caps, I put a ecc81/12AT7 in V1 and changed the speaker for a TREX and bingo, sounds great i'm into SRV. I can find schematics for the fender but nothing decent for the valveking, so I wanted to know which was V1, you answered that and I am very greatfull, what do you think of the 12AT7 in V1 on the Peavey ?
@@ronnocm8633 I have the schematic for the VK if you want it. At the end of any video you'll see an end graphic with my email on it, contact me via that. I prefer an 12AY7 to the ECC81 if it's a gain reduction you are looking for.
@@stuartukguitarampguy5830 Theres a website cant see an email
thank you so much for this!
Glad you enjoyed it Roy.
STUART, What are grid leakage and grid stopper resistors used for? the grid leakage is leaking the AC peak to peak voltage to ground which I'm guessing the term leakage means a voltage drop? and the grid stopper is stopping what? the AC peak to peak voltage from going into the tubes grid. The terms Stopper and Leakage I'm confused about why they are calling them stoppers and leakage and what they mean by them
Hi Wayne. These are archaic terms and not very helpful really! The 'grid stopper' is in series wih the grid. The grid has a capacitance to ground, so with this resistor you have a low pass filter. 'Low Pass' means 'High Rejection' - so it's rejecting (attenuating) high frequencies such as radio frequencies. Without this that amp would becoame a passable radio receiver. Think of it maybe as STOPPING the high frequencies. The 'grid leakage' resistor is conected from the grid to ground. It provides bias for that valve (basically without it there's no path to ground from the grid - it would be 'floating'. ) A downside of this resistor is that it attenuates the signal from the previous stage and hence reduces its level. I hope that helps.
@stuartukguitarampguy5830 thanks for the help and information. I was confused why they call those resistors grid stop and grid leakage. I get what your wrote it helps out
@@stuartukguitarampguy5830 I think the Tubes Grid is "leaking" positive DC voltage that is why you need to connect a "pull down/leakage" Resistor to pull down the grid leakage voltage to ground 0 volts. If no Grid leakage resistor the grid is Floating which can cause oscillations, unstable issues, noises.
@@waynegram8907 That's true but it's not the best way to look at it. A better way is just to say that the grid needs a bias voltage on it so that the cathode can be negative with respect to it. The bias voltage in this case is 0V and the grid resistor ensures this.
@@stuartukguitarampguy5830 What do you mean by the Cathode can be negative with respect to the grid at 0 volts? The Cathode would have to be BELOW 0 Volts -10vdc to -30vdc?
Thank you
can you do one for the triple X....
Hi Jay What is the triple x?
@@stuartukguitarampguy5830 peavey amp.. my first real badass amp I got around 2001 and it just died... dont know why... not places around me that fixes them... had a guy looking at it... he does some stuff with amps... its got him stumped... I have another one, but thats my baby...
thank you!
Glad you enjoyed it.
👍👍
how come every time I drink too much beer, I get shocked?
Ho ho!
Thanks Stuart! Youre tha man!