If you switch off the amp with the standby switch in the 'play' position, the filter caps will begin to drain via the tubes while their cathodes are still hot. The caps may discharge fully before the tubes stop conducting as their cathodes cool down, but they may not.
Thank you for doing a clear and concise how-to. You spoke at a rate slow enough for information to sink in, but not so slow as to be boring, and with a tone that's not at all condescending. I wish all instructional videos were like this. Thank you!
Thank you. You are an excellent presenter. I learned so much from this video (including what I was looking for in the first place). Your style had a lot to do with that. It’s an important subject for me because : (1) I learned the hard way about the need for capacitors to be allowed to bleed off. Not a nice experience… (2) my friend Pete was electrocuted for a long time (it held him rather than than throw him) because too-big a fuse had been fitted to an amp for the sake of expediency. He spent nine years (!!) in a hospital bed, as a result; (3) I saw the sad knock on effect on Alex Harvey (Sensational Alex Harvey Band) after his brother, Les was electrocuted and killed on stage while playing guitar for Stone the Crows. Many reports talk about him touching ‘an unearthed microphone’ but his roadie knew what was really happening and eventually managed to kick the plug out of the guitar amp (getting zapped and burned in the process because the thing was practically exploding). Poor Alex (an amazing front man) was never the same again after Les died. As you say, never underestimate a tube amp…
When you remove the doghouse cover that shields the array of power capacitors you can accidentally bump the metal box against the live leads of those caps and shock yourself. Do not flip an amp over and just remove that cover straightaway. There is a way to discharge those big power caps from the inside of the chassis via their connecting leads. It's always better to discharge them from inside. Also, if you're working on an amp with a standby switch, turning the amp off while leaving the standby switch engaged is also a good preliminary method for draining power caps ... but you'll still want to verify that there is no power by checking with your multimeter.
Question: using the dog house method was more about isolating the power caps from the signal path than "to protect you", right? In the same era you had at least Champs, Princetons, and Deluxes that had the filters inside the chassis, which leads me to think that the component layout of the Showman necessitated getting creative.
Your explanation about the heart valves being closed at the same time and then receiving a lethal voltage and your heart valves will never open again is the best WARNING ever. I will never forget it. You were right o the point, you did not imply I could get hurt, nope, you explained exactly how it could happen. So now I too will always keep one hand in my pocket while exploring/working on my tube amps. Thank you Mr. Kennedy!
On at least two occasions in my life I have had voltage run up my left arm and to the shoulder. I was young enough and reacted fast enough to disengage. The voltages never reached my heart. First time at around age 10 I stuck my finger in a lamp socket to see what would happen! Current ran up my arm. I was fast enough to pull my finger out. Second time I was trying to fix my friends car at night while it was running. I grabbed a spark plug and that DC voltage shot straight up to my shoulder. I was lucky that I was able to move my muscles and I was able to let go. I'm 67 now and I doubt that my reflexes are fast enough to disengage. A third time I pulled on a lawn mower spark plug wire and just got voltage into my finger tips. I am aware that sometimes you cannot disengage because the current is so strong that it locks up your muscles. That's how I envisioned being electrocuted to death. Now you have taught me that the current only needs to reach your heart while both valves are closed and that's all she wrote as they will never open again. Again I thank you Mr. Kennedy, Peter
I also have 25 years of occasional work experience repairing electronics. When I was in electronics school (National Radio Institute), our very large TV stoped working. This was before my TV servicing lessons. I tried taking the cathode wire off of the CRT with just a pair of metal forceps (not a grounded flat screw driver). The shock I got make me feel like dying (literally). Another time I got shocked off of a large Lyden Jar that I made and charged with a 500,000 volt Van de Graff generator. As you know, the Lyden Jar is a huge capacitor, and the three inch spark hit my thumb, sending me to the hospital. Frank Frank Reiser Video/Audio Service
I'm well aware of discharging caps and verifying their low voltage, but I recently had my amp opened up for some extensive mods for about 2 weeks. When I was done, I played my amp for a couple hours and then opened it up again. I started probing around with my electrical tape-covered chop stick (the result of irrational anxiety) for about 5 seconds before I realized I hadn't discharged the caps!! I have nightmares about getting shocked or setting fire to my current limiter, but since I had worked on my amp for so long without discharging the caps, I momentarily forgot to do it!!! That was scary!!! Now I have a big sign in front of my work bench to remind me on the off-chance I space it again!!!
I've never seen a red chopstick before - they're usually just natural wood color. Always good to have him tell you what it is, so someone doesn't think it's a metal rod. :-)
After making sure that the filter caps are discharged , double check it again . then check the ESR in those caps. ESR = equivalent series resistance. Also look for leakage on the outside of the cap .
I have my first tube amp being delivered tomorrow. Great information and was presented so well. Thank you. I was a corporate aircraft mechanic for 32 years. You should make training videos for technicians. Well done.😊
In the intro, I thought it was a bit presumptuous that you referred to yourself as the Tube Amp Guru. However, I watched the video and believe that you accurately accessed your skill level.
Let me first start by saying "Thank You" for the video. Us Noobs around the globe are in need of such clear and concise information. That being said, I do have a very serious question, and then I'll explain why I'm asking said question. Both when discharging and testing the filter caps for residual voltage, can the ground lead of the same capacitor be used instead of the chassis of the amplifier? The reason I ask this question is, what if there's a broken ground circuit? If the ground circuit were to somehow break, then it would seem that using the chassis for your ground discharge and voltage test would give you a false reading.
Hey Rob, this is from Jeff Bober, dude behind Budda Amplification and East Amplification who writes our monthly Ask Amp Man column: "Rob, thanks for your question. Yes, you can certainly use the ground side of the capacitor to discharge it. It's actually a good point and a good idea! " Best of luck and be safe!
101 note: the amp must plugged in order to get the ground conection. In some countries there is no a standard conection to ground, so if you don't have any ground conection in your bulilding there would be dangerous to plug in your amp. You must have a Ground conection.
Good catch! Was hoping somebody had already mentioned that. Some shops have a copper strip or plate that is wired to earth ground, and you just connect the chassis to it via a test lead.
Most important comment and correct. How do you move this comment to the top of the list? Unfortunately all the entertaining info, not good info, moves to the top-good thing I love entertaining TH-cam comments.
Hello Kye, thanks for this advice. Your description of those two heart valves should make believers out of your viewers. I have had my share of 120V shocks, but have grown to be a lot more respectful of what's under the hood. Keep up the good work. Tnx from the west coast of Canada. - c
This is what I don’t get yet people keep talking about it. For example how is the planet the biggest resistor or whatever he said if the amp isn’t connected to it directly? Where is all that voltage going to?
@@user-yf3ns9bx6nI’m not an electrician but I think in this case the metal chassis is the “earth” and that’s why you leave your opposite hand in your pocket so you don’t accidentally touch and become a part of the “earth” when discharging high voltage current from the capacitors.
You should also check the voltmeter itself before use. For example by probing a battery. Otherwise something like a broken wire can result in a zero reading even tough there is dangerous voltage in the capacitor.
I once had a start capacitor blow on my well pump in the basement. It sounded as if someone fired a .38 down there. It went off like a party popper, there was about 10 feet of uncoiled brown paper on the floor. The crazy part is that it blew off the screwed down metal dog house that was mounted on top of the pump motor. They're powerful little things.
Thank you very much for this tutorial! Not only was the content very helpful, but also was your amazing and methodical explanation (inspiring teachers like me)!
Very good intro to a total noob like me who just purchased his first used tube amp. Had no idea of the high voltages in there. I have great respect of household appliances and car batteries, but I used to believe anything related to stereo, hifi or guitar equipment was completely harmless in terms of the currents and voltages involved. Evidently, that is not so. :-) A couple of places could have benefited from more detailed information: When testing the fuse continuity with the voltmeter, what settings do I use? And when bleeding the capacitors, do I want the amp plugged into a power outlet or not? I'm guessing not, but how can the chassis be grounded when it's sitting on a rubber mat and unplugged from the wall outlet?
Hey Kye ! ! Great video my friend. While being extremely informative, you cover all the what if questions by repeating what you've gone over. Great vibe Bro ! ! ! Very helpful.
Thank you for this great tutorial. I need to open my amp in order to look for loose contacts or broken solder points, but was afraid of the high voltage, since I did not know how to discharge the caps (yes, in theory I know, but never seend practical).
Thank You so much Kye. Such valuable info to keep in my video archives to view before I work on my Marshalls and Fender amps at every working episode. I really enjoy my tube amps and love to play with tube selections for various tones. This is a great reminder every time. Best Regards Shane
Great vid. About to do my first filter change and this tut was by far the easiest to understand, shown well. Thanks! How about a vid on changing out a pre amp tube socket??
So, we unplug the amp to test fuse....makes sense. When you refer to off-loading Cap charges to the "largest ground there is...Earth," are you implying that the amp should again be plugged in when properly discharging unwanted DC voltages as stored in Filter Capacitors? If so, that's a huge piece missing from the video. What would happen if I attached the other ned of discharge lead to chassis and it wasn't plugged into mains? Would it still dissipate? Where would the charge ultimately go?
That part was not explained well, or at all. No, you don’t need earth ground, you use chassis ground which also for example is connected to the negative side of the capacitor. Just like if you dead short a battery you drain it, same here. You are connecting the negative and positive of the cap which drains it.
As JusAequum asked. How do you know the chassis is grounded. I understand how it would be grounded if the amp is plugged in but if the amp isn't plugged in how is it grounded?
This is so useful for a complete beginner like me, thank you. But I don't understand how we are discharging to ground via the chassis if the amp is not plugged in - how does the voltage actually reach ground ?
Something about the way this guy describes the dangers of working with electricity really makes you understand how dangerous it really is. I'd even not dare break his rules because he was so intimidatingly factual about how you can die doing this.
If the amp was unplugged, how can the case be considered a grounding point? The whole thing is floating. Don't the filter capacitors need a path to true ground in order to discharge correctly?
Well i think you just unplug the power for testing the fuse (no fuse with power plug, no safety). Then plugging it in for bleeding the Capacitors. Correct me if im wrong.
ironcut13 Well, you can die 30,000 feet in the air but that's besides the point. Most amps have their metal case connected to circuit ground, for shielding. Then the case becomes connected to earth when (properly) plugged in, for safety. If for some reason the case/chassis is not grounded, you can discharge the caps to some other poit at ground potential, like their negative side.
Unless you disagree, there are amps where the filter caps are not accessible for discharge, for example when mounted on a circuit board that is on standoffs and they are standing caps. So if you have access to the schematic one can always find a point on the component side (usually resistor lead for example for the bleed resistors) and do th discharge trick there as well. Right?
I would add that on the old ungrounded tube amps there is a voltage potential to electrical earth ground and it depends on the AC plug polarity. Some old amps had a polarity switch to change that will reduce the shock risk. The way to test for a potential chassis ground voltage shock is set your multimeter to AC volts, in a range that can cover 120 volts. Connect one terminal to the amp's chassis ground and then touch the other meter probe into the AC wall outlet ground terminal. If there is a voltage potential you might see something between 50 and 100 volts AC. Changing the ground switch will reduce that voltage to a safe level. If the amp does not have a polarity switch then the AC plug's polarity must be reversed. This was a common issue with Hammond organs and the Leslie 122 and 145 amps. If the AC plug's polarity made the chassis hot with voltage, when someone touches the organ's metal chassis and their mouth to a microphone which is connected to a grounded sound system, they would get shocked. So I always checked for that leakage voltage when working on a Hammond.
@@keyboardtek Sorry. I was asking can you get electrocuted if you just play the guitar plugged in tube amp? I mean if you don't open it up to change tubes and modify it.
@@aloroki3350 If it is a very old tube amp that has a polarity selecting switch for a power switch, then you have the potential for getting a shock only if you are touching any metal on your guitar and also touching some other electrical equipment that has a proper earth ground. By only touching your guitar itself you are unlikely to get a shock. In the old days the guitarists that I worked with would hold the strings on their guitar and quickly touch the microphone they had to sing into with their finger. If they got a shock, they changed the polarity switch. Many found out the hard way when they first sang into the mic and got shocked through their mouth! Any new amps that have a grounded plug and no polarity switch does not have this shock problem.
thanks so much for the detailed video.I'm trying to fix my used mesa boogie 50/50 and have been electrocuted enough in my life so i want to avoid any more shocks if i can help it. going to get a multimeter,resistor and gator clips this week so i can work on the amp.i didnt know that the caps can dry out so i need to figure out how old they are(amp made in 1990) or if they've been replaced.
To be sure the caps are discharged, how do you feel about the need to or not to turn the standby switch on if there is one? D-LaB Tech has a video about that aspect.
Someone out there was talking about an amp where the standby switch was wired so as to disconnect the ground to the chassis I think. In that case when using the chassis as ground with the standby switch in the off position I think you neither drain nor can get a true reading of residual voltage. You ought to have a copy of and understand the schematic before getting in there.
The gun is always loaded, the horse always kicks, the dog always bites and the filter caps are always fully charged.
And she will always love you!
Unless the mains is disconnected and the standby switch has been on for more than 30mins.
I'm still going to check before I stick my fingers in there!
If you switch off the amp with the standby switch in the 'play' position, the filter caps will begin to drain via the tubes while their cathodes are still hot. The caps may discharge fully before the tubes stop conducting as their cathodes cool down, but they may not.
Always work on tube amps with one hand in your pocket.
Thank you for doing a clear and concise how-to. You spoke at a rate slow enough for information to sink in, but not so slow as to be boring, and with a tone that's not at all condescending. I wish all instructional videos were like this. Thank you!
Thank you. You are an excellent presenter. I learned so much from this video (including what I was looking for in the first place). Your style had a lot to do with that.
It’s an important subject for me because : (1) I learned the hard way about the need for capacitors to be allowed to bleed off. Not a nice experience… (2) my friend Pete was electrocuted for a long time (it held him rather than than throw him) because too-big a fuse had been fitted to an amp for the sake of expediency. He spent nine years (!!) in a hospital bed, as a result; (3) I saw the sad knock on effect on Alex Harvey (Sensational Alex Harvey Band) after his brother, Les was electrocuted and killed on stage while playing guitar for Stone the Crows. Many reports talk about him touching ‘an unearthed microphone’ but his roadie knew what was really happening and eventually managed to kick the plug out of the guitar amp (getting zapped and burned in the process because the thing was practically exploding). Poor Alex (an amazing front man) was never the same again after Les died.
As you say, never underestimate a tube amp…
Thanks Kye! You've convinced me! I'm gonna put my hand in my pocket to get my wallet out and hire a tech to do this for me. Thanks Man!!
Brilliant!
When you remove the doghouse cover that shields the array of power capacitors you can accidentally bump the metal box against the live leads of those caps and shock yourself. Do not flip an amp over and just remove that cover straightaway. There is a way to discharge those big power caps from the inside of the chassis via their connecting leads. It's always better to discharge them from inside. Also, if you're working on an amp with a standby switch, turning the amp off while leaving the standby switch engaged is also a good preliminary method for draining power caps ... but you'll still want to verify that there is no power by checking with your multimeter.
Question: using the dog house method was more about isolating the power caps from the signal path than "to protect you", right? In the same era you had at least Champs, Princetons, and Deluxes that had the filters inside the chassis, which leads me to think that the component layout of the Showman necessitated getting creative.
Notice how Kyle drew on his experience and was careful to lift the doghouse vertically, avoiding contact with the capacitor leads.
having replaced a filter cap in my marshall, I get ya.
Best to use gloves :)
@@kornelijekovac9793what kind of gloves?
Thank you! A lot of guys say to make sure the amp is safe before working on
it but you're the only person I've found who shows how it's done.
Your explanation about the heart valves being closed at the same time and then receiving a lethal voltage and your heart valves will never open again is the best WARNING ever. I will never forget it. You were right o the point, you did not imply I could get hurt, nope, you explained exactly how it could happen. So now I too will always keep one hand in my pocket while exploring/working on my tube amps. Thank you Mr. Kennedy!
On at least two occasions in my life I have had voltage run up my left arm and to the shoulder. I was young enough and reacted fast enough to disengage. The voltages never reached my heart. First time at around age 10 I stuck my finger in a lamp socket to see what would happen! Current ran up my arm. I was fast enough to pull my finger out. Second time I was trying to fix my friends car at night while it was running. I grabbed a spark plug and that DC voltage shot straight up to my shoulder. I was lucky that I was able to move my muscles and I was able to let go. I'm 67 now and I doubt that my reflexes are fast enough to disengage. A third time I pulled on a lawn mower spark plug wire and just got voltage into my finger tips.
I am aware that sometimes you cannot disengage because the current is so strong that it locks up your muscles. That's how I envisioned being electrocuted to death.
Now you have taught me that the current only needs to reach your heart while both valves are closed and that's all she wrote as they will never open again.
Again I thank you Mr. Kennedy,
Peter
Except it’s not accurate. The theory sounds nice and smart. However, completely wrong.
Cause I've got one hand in my pocket, and the other one is probing a valve amp.
If Alanis taught us one thing, it's safety. haha
hahaha
I was waiting for this haha
I've got something in my pocket for you. why don't you reach in and see what it is?
It's candy, I knew it. A rolo.
Best explanation I have seen.... well done.
I would add: Stand on a rubber mat and not a concrete floor.
Put boots on it can save your ass
I’ve been standing on a metal floor is that OK?
@@cardbored_ I've been working on my amps in the rain dressed like that tin guy from wizard of Oz. Will I be okay?
I also have 25 years of occasional work experience repairing electronics. When I was in electronics school (National Radio Institute), our very large TV stoped working. This was before my TV servicing lessons. I tried taking the cathode wire off of the CRT with just a pair of metal forceps (not a grounded flat screw driver). The shock I got make me feel like dying (literally). Another time I got shocked off of a large Lyden Jar that I made and charged with a 500,000 volt Van de Graff generator. As you know, the Lyden Jar is a huge capacitor, and the three inch spark hit my thumb, sending me to the hospital.
Frank
Frank Reiser Video/Audio Service
And now everytime somebody runs the microwave you pee your pants right?
Easily the most informative video I've stumbled upon for beginners.
I'm well aware of discharging caps and verifying their low voltage, but I recently had my amp opened up for some extensive mods for about 2 weeks. When I was done, I played my amp for a couple hours and then opened it up again. I started probing around with my electrical tape-covered chop stick (the result of irrational anxiety) for about 5 seconds before I realized I hadn't discharged the caps!!
I have nightmares about getting shocked or setting fire to my current limiter, but since I had worked on my amp for so long without discharging the caps, I momentarily forgot to do it!!! That was scary!!!
Now I have a big sign in front of my work bench to remind me on the off-chance I space it again!!!
I've been trying to think of a way to mistake proof this kind of error - but to err is human ... I guess we're doomed ;)
thank you for keeping it simple! learning new stuff at 72.
"This... is a chopstick..." lol! Thats the best!
I've never seen a red chopstick before - they're usually just natural wood color. Always good to have him tell you what it is, so someone doesn't think it's a metal rod. :-)
It was like, “This is a ...... chopstick. Am I going to fast for some of you?”
After making sure that the filter caps are discharged , double check it again . then check the ESR in those caps. ESR = equivalent series resistance. Also look for leakage on the outside of the cap .
Having spent many hours with Kye I can tell you he knows exactly what he is doing and is one of the best...
I have my first tube amp being delivered tomorrow. Great information and was presented so well. Thank you.
I was a corporate aircraft mechanic for 32 years. You should make training videos for technicians. Well done.😊
In the intro, I thought it was a bit presumptuous that you referred to yourself as the Tube Amp Guru. However, I watched the video and believe that you accurately accessed your skill level.
More thorough and with better production than several other similar video lessons.
Best safety video by far! Great work guys! Keeping people safe and alive for 8 years!
Thank you for not neglecting the safety aspect .you never know who could be watching these videos.
Let me first start by saying "Thank You" for the video. Us Noobs around the globe are in need of such clear and concise information. That being said, I do have a very serious question, and then I'll explain why I'm asking said question.
Both when discharging and testing the filter caps for residual voltage, can the ground lead of the same capacitor be used instead of the chassis of the amplifier?
The reason I ask this question is, what if there's a broken ground circuit? If the ground circuit were to somehow break, then it would seem that using the chassis for your ground discharge and voltage test would give you a false reading.
Hey Rob, this is from Jeff Bober, dude behind Budda Amplification and East Amplification who writes our monthly Ask Amp Man column: "Rob, thanks for your question. Yes, you can certainly use the ground side of the capacitor to discharge it. It's actually a good point and a good idea! " Best of luck and be safe!
What exactly is the ground lead of the same capacitor ?
101 note: the amp must plugged in order to get the ground conection.
In some countries there is no a standard conection to ground, so if you don't have any ground conection in your bulilding there would be dangerous to plug in your amp. You must have a Ground conection.
A three prong ground. The middle prong is actually the ground lead.
But remember : at the electrical junction box the neutral and ground are tied together. Just a thought.
I came to the comment section looking for this
Good catch! Was hoping somebody had already mentioned that. Some shops have a copper strip or plate that is wired to earth ground, and you just connect the chassis to it via a test lead.
Most important comment and correct. How do you move this comment to the top of the list? Unfortunately all the entertaining info, not good info, moves to the top-good thing I love entertaining TH-cam comments.
Hello Kye, thanks for this advice. Your description of those two heart valves should make believers out of your viewers. I have had my share of 120V shocks, but have grown to be a lot more respectful of what's under the hood. Keep up the good work. Tnx from the west coast of Canada. - c
Clear. Concise. You have the the gift of a teacher.
How is the chassis grounded if you've unplugged the amp?
This is what I don’t get yet people keep talking about it. For example how is the planet the biggest resistor or whatever he said if the amp isn’t connected to it directly? Where is all that voltage going to?
@@user-yf3ns9bx6nI’m not an electrician but I think in this case the metal chassis is the “earth” and that’s why you leave your opposite hand in your pocket so you don’t accidentally touch and become a part of the “earth” when discharging high voltage current from the capacitors.
You should also check the voltmeter itself before use. For example by probing a battery. Otherwise something like a broken wire can result in a zero reading even tough there is dangerous voltage in the capacitor.
I once had a start capacitor blow on my well pump in the basement. It sounded as if someone fired a .38 down there. It went off like a party popper, there was about 10 feet of uncoiled brown paper on the floor. The crazy part is that it blew off the screwed down metal dog house that was mounted on top of the pump motor. They're powerful little things.
Best video on yt regarding safety by discharging filter caps. Thanks
I'm about to order a DYI kit and just anted to actually see this being done! Thank you!
How did your build go
Thank you for this amp PSA. I’m going to start working on my amp and was doing preliminary research as there aren’t any good techs near me.
Thank you Kye and Premier Guitar, this is gold!
Great video, but how can the amp be earthed when not plugged in?
Great video. Nice choice of music up there on the shelf.
Thanks, Kye . Been a tech for many years and I appreciate your video.
This is really good info. If this was around 30 yrs ago, it would have saved me a lot of painful reminders.
"The fuse is your friend..."
Excellent video - many thanks.
I followed this advice to the letter - but now I have chow mein in my amp
The President of The Internet Lmao
Thank you very much for this tutorial! Not only was the content very helpful, but also was your amazing and methodical explanation (inspiring teachers like me)!
I am not familiar w electrical repairs but for the first time ever I actually understood some. Great vid. Very good indeed. Thanks
Very good intro to a total noob like me who just purchased his first used tube amp. Had no idea of the high voltages in there. I have great respect of household appliances and car batteries, but I used to believe anything related to stereo, hifi or guitar equipment was completely harmless in terms of the currents and voltages involved. Evidently, that is not so. :-) A couple of places could have benefited from more detailed information: When testing the fuse continuity with the voltmeter, what settings do I use? And when bleeding the capacitors, do I want the amp plugged into a power outlet or not? I'm guessing not, but how can the chassis be grounded when it's sitting on a rubber mat and unplugged from the wall outlet?
The capacitors are where the danger lies
Really appreciate the clear and concise explanation! It’s clear that you really are an expert Mr. Kennedy
Finally someone on youtube explains this properly!
Just came across this safety tutorial you posted some years ago. You are an excellent teacher, thank you.
Hey Kye ! ! Great video my friend. While being extremely informative, you cover all the what if questions by repeating what you've gone over. Great vibe Bro ! ! ! Very helpful.
I love tube amps, I love '59s, I love the crunch. But if there's one thing I love the most,...
it's safety.
I didn't even dare to interrupt this video once
Love this but I think you should reform The Proclaimers!
lol!
😆
Fantastic! Very well explained. Thank you.
Great video thanks. The heart simulation was great!
By far the most helpful and clear video on this subject! Helped me out a lot.
Excellent video. Thank you for recording and posting this!
and dont use a pencil to poke around as the graphite can conduct electricity.
I wondered...
Wow I completely forgot about this , great point.
Thank you for this great tutorial. I need to open my amp in order to look for loose contacts or broken solder points, but was afraid of the high voltage, since I did not know how to discharge the caps (yes, in theory I know, but never seend practical).
Thanks for debugging the filter cap debate.
Thank You so much Kye. Such valuable info to keep in my video archives to view before I work on my Marshalls and Fender amps at every working episode. I really enjoy my tube amps and love to play with tube selections for various tones. This is a great reminder every time.
Best Regards
Shane
Wow thank you. I feel a lot better doing the little things I do to my amp now.
Great vid. About to do my first filter change and this tut was by far the easiest to understand, shown well. Thanks! How about a vid on changing out a pre amp tube socket??
Is the amp really grounded if it’s unplugged? Shouldn’t it be jumped to a known ground?
Thanks for clearing up the mystery.
So, we unplug the amp to test fuse....makes sense. When you refer to off-loading Cap charges to the "largest ground there is...Earth," are you implying that the amp should again be plugged in when properly discharging unwanted DC voltages as stored in Filter Capacitors? If so, that's a huge piece missing from the video. What would happen if I attached the other ned of discharge lead to chassis and it wasn't plugged into mains? Would it still dissipate? Where would the charge ultimately go?
That part was not explained well, or at all. No, you don’t need earth ground, you use chassis ground which also for example is connected to the negative side of the capacitor. Just like if you dead short a battery you drain it, same here. You are connecting the negative and positive of the cap which drains it.
Cool. Thank you. What wold habe been interesting is how to calculate what fuse to use on a DIY Amp.
This is a fantastic video...thank you. It's simple...down to earth and easy to understand. Great job.
Excellent safety video. Thank you greatly.
Thank you for taking the time to make this video.
As JusAequum asked. How do you know the chassis is grounded. I understand how it would be grounded if the amp is plugged in but if the amp isn't plugged in how is it grounded?
It isn’t. You are shorting the caps one by one to their negative lead. Just as you can short a battery and it drains it with no path to ground.
Great information! Good teacher.
Amazing video, extremely clear and easy to follow. Also very reassuring. Cheers!
Excellent...thank you!
Thanks Kye! You saved my life
Where is the I love it! button?
Great tech and clean info!
Thanks for this info on amp repair safety.
This is so useful for a complete beginner like me, thank you. But I don't understand how we are discharging to ground via the chassis if the amp is not plugged in - how does the voltage actually reach ground ?
Thank you for the information, I got an electric shock tonight when I plugged in guitar so was looking up any help.
This is an excellent explanation and process video. Well done
great video! thank you from october 2021
On second thought. I think I'll send my amp out to get fixed.
HI Mr Kennedy, fantastic video. Beautifully explained. Blessings for the info!
Fantastic video. I'm looking forward to some circuit theory, too!
Something about the way this guy describes the dangers of working with electricity really makes you understand how dangerous it really is. I'd even not dare break his rules because he was so intimidatingly factual about how you can die doing this.
Just the way he had his hands simulating a heart failing gave me nightmares lol
@@BOTiTTE Me too. I'm now terrified to even look at my amp!
I’m switching to drums!
Outstanding Video Kye, thank you.
Very clear & concise - thank you for the video
+1 for Trower CD!
If the amp was unplugged, how can the case be considered a grounding point? The whole thing is floating. Don't the filter capacitors need a path to true ground in order to discharge correctly?
Well i think you just unplug the power for testing the fuse (no fuse with power plug, no safety). Then plugging it in for bleeding the Capacitors. Correct me if im wrong.
Yeahhh, How can you bleed the capacity to the big EARTH if the amp is not plugged to it?
The chassis is connected naturally to earth, as your feet ! You can die even if you're not plugged, no ?
ironcut13 Well, you can die 30,000 feet in the air but that's besides the point.
Most amps have their metal case connected to circuit ground, for shielding. Then the case becomes connected to earth when (properly) plugged in, for safety.
If for some reason the case/chassis is not grounded, you can discharge the caps to some other poit at ground potential, like their negative side.
***** their negative side are connected to the ground, as the chassis, so ...no matter if the amp is plugged or not
Unless you disagree, there are amps where the filter caps are not accessible for discharge, for example when mounted on a circuit board that is on standoffs and they are standing caps. So if you have access to the schematic one can always find a point on the component side (usually resistor lead for example for the bleed resistors) and do th discharge trick there as well. Right?
Very good explanation.
Thank you for this great video with crystal clear informations !
Excellent video. What about newer single amps like a Blackstar Studio 10 with odd PCB configurations?
Nice and thorough.
comedic genius at work.
I would add that on the old ungrounded tube amps there is a voltage potential to electrical earth ground and it depends on the AC plug polarity. Some old amps had a polarity switch to change that will reduce the shock risk. The way to test for a potential chassis ground voltage shock is set your multimeter to AC volts, in a range that can cover 120 volts. Connect one terminal to the amp's chassis ground and then touch the other meter probe into the AC wall outlet ground terminal. If there is a voltage potential you might see something between 50 and 100 volts AC. Changing the ground switch will reduce that voltage to a safe level. If the amp does not have a polarity switch then the AC plug's polarity must be reversed. This was a common issue with Hammond organs and the Leslie 122 and 145 amps. If the AC plug's polarity made the chassis hot with voltage, when someone touches the organ's metal chassis and their mouth to a microphone which is connected to a grounded sound system, they would get shocked. So I always checked for that leakage voltage when working on a Hammond.
Hi. I want to get my first tube amp in future. Is it dangerous when you don't open it on your own, and bring it to the mechanic to do regular service?
@@aloroki3350 Your question does not make sense to me.
@@keyboardtek Sorry. I was asking can you get electrocuted if you just play the guitar plugged in tube amp? I mean if you don't open it up to change tubes and modify it.
@@aloroki3350 If it is a very old tube amp that has a polarity selecting switch for a power switch, then you have the potential for getting a shock only if you are touching any metal on your guitar and also touching some other electrical equipment that has a proper earth ground. By only touching your guitar itself you are unlikely to get a shock. In the old days the guitarists that I worked with would hold the strings on their guitar and quickly touch the microphone they had to sing into with their finger. If they got a shock, they changed the polarity switch. Many found out the hard way when they first sang into the mic and got shocked through their mouth! Any new amps that have a grounded plug and no polarity switch does not have this shock problem.
@@keyboardtek Thank you very much for explanation, it helped me to understand this. Have a good day.
Excellent class. How do you check if the filter capacitors are good?
Excellent video....
thanks so much for the detailed video.I'm trying to fix my used mesa boogie 50/50 and have been electrocuted enough in my life so i want to avoid any more shocks if i can help it. going to get a multimeter,resistor and gator clips this week so i can work on the amp.i didnt know that the caps can dry out so i need to figure out how old they are(amp made in 1990) or if they've been replaced.
Thanks Kye; very instructive video!
A truly well done video, thank you!
To be sure the caps are discharged, how do you feel about the need to or not to turn the standby switch on if there is one? D-LaB Tech has a video about that aspect.
Saw the same vid. It totally made sense, so I’ll be discharging caps with standby on and then again with standby off, then meter check them.
Someone out there was talking about an amp where the standby switch was wired so as to disconnect the ground to the chassis I think. In that case when using the chassis as ground with the standby switch in the off position I think you neither drain nor can get a true reading of residual voltage. You ought to have a copy of and understand the schematic before getting in there.
Excellent video!
Thank you, very clear and concise.