Thank you Mark. You are the only one, among many, that has dealt with this issue in a professional and code compliant sense (although some jurisdictions require a earth-ground metal chassis regardless of what other measures are in place). First priority is safety. Hums / ground loops are secondary to be dealt with separately. I used to build custom control systems which required a 'special' inspection /approval process by the local electrical authority. Not only did the Hammond metal cabinet require an earth ground but the door had to be electrically bonded to it even though it too was metal with a metal "piano" hinge and it had to be tied with ring terminals. No spade connectors allowed. The neutral is NEVER switched alone including fusing. I Thanks again for this.
Finally, a video that covers the topic well and discusses all the decent options. Now I can point folks (customers) here to educate themselves. Thanks Mark. Well done.
I have a fender twin reverb guitar amplifier. I threw away the two prong cable and installed a three prong one. I grounded the cable at the base of the power supply transformer and cut out the dearh capacitor. No problems since then. Better safe than sorry! Nice video!
Thank you so much for this. I have a basic background in theory from my electrical apprenticeship and the way this is all presented makes perfect sense to me. This will be the video I send to other people to explain the concept. I filled in a ton of gaps with this thanks.
Thank you. As a chemist, I had to work on older equipment. The electronics people helped me deal with death capacitors and other safety issues. Thanks again. Happy New Year.
At first I thought this was about old paper type capacitors that fail, start passing current and destroying electronic parts but now I see its about the equipment trying to kill people. Years ago we had a lot of old tube amps for my brothers band and you had to pay attention how things were plugged in. One time I watched my brother step up to microphone and get big blue flash right in his lip
My first live performance in 1966, I had a tiny amp for a mic and another tiny amp for my guitar. As soon as my lips touched the mic, I was almost knocked out and my face was uncomfortably numb for about a half-hour. It took me another 30 years before I was able to shake my mic shyness.
"Hot" chassis in tube radios was quite common up into the 1950's. My father taught me how to properly orient the plug using an NE-51 neon bulb with a resistor.
The capacitor layouts may be common to audio amplifiers but transceivers (two way radios) almost always have at a bare minimum a cap from hot to chassis ground and one from neutral to chassis ground. For this application some vintage tube radios used a (popular at the time) very large ceramic disc capacitor that had 3 terminals. It was basically two capacitors in one ceramic capacitor package. Some radios used a 3 capacitor layout. The two mentioned above and another across the hot and neutral. In solid state units that did not have a 3 prong earth ground type cord it is also common to have a high resistance resistor tied from the common line to the chassis for a earth reference. In ANY radio and I mean ANY vintage radio be it solid state or vacuum tube type always replace all these capacitors. The ceramic types fail just like old paper caps did. Only difference is they dont slowly short out over time. They go from working perfectly to dead short. They are attached to the mains any time the cord is plugged in and get the snot beat out of them by power line surges. I have seen several dozens of them that have exploded over the years. One that even caught the radio on fire when it shorted out in a Tram D201 CB radio. When it shorted out near the power transformer it caught the transformer insulation paper on fire. You can find modern x1 y2 rated capacitors from almost all the large electronic supply companies like DigiKey, Allied, Houser, Newark, etc. Most of the time the problem is people have a hard time finding them on their websites because they don't know what ratings to search for. A good source if you work on tube gear is www.justradios.com . David and Babylyn have a simple to navigate website and sell these capacitors. All the capacitors they sell are on one large page. They specialize in repair parts for tube gear.
Great job ! I understood all of that. I especially appreciate the information regarding the different recommended approaches for handling a vintage guitar amp versus a vintage piece of audio gear, since I own both. Than you very much.
Greetings. As the author of the "infamous" Death Cap video referenced in your presentation, I feel obligated to offer some insights. 1.) The video was created 6 years ago and is somewhat simplistic in its approach, as was my understanding at the time, but it was an honest attempt to bypass the hysteria and factually evaluate "Death Capacitors" in circuit. 2.) I use the rather imprecise term "hum" to cover all extraneous noise which could enter the circuit via the primary wiring. 3.) To be more thorough, I should have reversed the AC plug and repeated the voltage and current measurements, but at no time would plug reversal ever result in "full AC voltage to the chassis" of any of the amplifiers. 4.) That said, my observations were based on the data at hand, rather than hearsay, and were offered as opinion.....to affect the handling of the vintage amps in my own collection, which I preferred to keep in original condition if possible. In the one case where the "Death Cap" demonstrated current flow to the chassis, it was removed. I personally see no issues with the conclusions and would caution people to recognize that opinion is not fact, regardless of whose opinion it is, and when opinion does not agree with your preconceived notions, it is not necessarily wrong. I enjoyed your video and found it to be quite thorough and well presented. You offer logical choices for the prevention of shock hazards and ground loops, which prove helpful to many viewers. Thanks for posting it.
Hello Uncle Doug. Didn't mean to stir up anything with that portion of my video, I just kept running across sites that quoted it as being flawed when I was making this video. As I mentioned, sadly I hadn't watched your video so in fairness, I probably shouldn't have posted that. I have the utmost respect for you and what you do.
I did find it a bit strange that you would take the time to cite my video as being flawed, especially since you had never watched it, but no doubt all videos that express opinions.....and all do.....are flawed to those whose opinion differs. Regardless, I found the portion of your video that was dedicated to the topic to be factual and very well done. Thank you for your effort in that regard.
@@UncleDoug I find it refreshing that you are owning up to any mistakes that may have been made. I also haven't watched your video on the topic, but I might have a look since I am studying up on the subject at the moment. May I ask, if there was indeed "not quite right" I guess you could say, information in that video, has it been amended to reflect the new information? Not to offend, just that if it was me, I would have made a change or two rather than leave it up. But as I said, I haven't watched it yet, you may have done this already. And yes, sadly when it comes to electronics, there can be different interpretations of the same basic knowledge unfortunately. I'm sure the majority of your info is more than solid. I will take a look in the morning and most likely subscribe to you as well! So great to have some actual experienced minds to watch and learn from!
@@ballsrgrossnugly The video was not amended......there is no means to do so, MM.......and I still feel that it served a valid purpose. I never said that it was "not quite right", but could have been more thorough......let's face it, so could virtually all such videos. It is still my contention that an intact "death capacitor" in an amp with a properly installed 3-wire chassis-grounding power cable is a non-issue.
@@UncleDoug Still awake lol maybe I should just watch the damn video instead of assuming huh? Yeah the way you explain it, it's at least not a safety issue. Maybe a buzz issue but that's not the point of a safety warning. Fair enough. I'll watch that video rather than comment any more and securely place my toes down my own throat!
Thank you, Mark. This is no joke at all. I got a huge zap from plugging my guitar into an old vintage Marshall amplifier that was in for repair at my buddy’s shop. The second l touched the strings, I thought my friend had run full speed across the shop and jammed his elbow between my shoulder blades or slammed me in the back with a baseball bat! It felt like a truck had hit me. He of course didn’t do that, but a big zap is a very scary thing that you don’t forget. This happened to me around 25 yrs ago. I am of course extra careful when I am poking around inside any gear since then, whatever it may. Use a chopstick to check around and keep one hand in your pocket.
same here, a Fender Quad reverb. I was standing up playing through the amp and for some reason I reached over to switch channels on a small TV and that's when a giant hand picked me up and threw me Gainst a wall, scared the living crud outvof me and taught me to double check all Earth/ground wires on ",Everything and to use a "Discreet" socket just to power my Guitar amp and nothing else, nastyvnasty shock!
Very good video lesson. Learned a long time ago that the caps didn't fail in the user's favor. Especially the radios with direct line-to-tube rectifier sets. All of my Heathkit equipment so far has had the two fat HV disc capacitors on both legs of the line cord to chassis. Wired as if they were safety caps. They are not! I always replace them with two X1Y2 safety caps and mark the neutral lead on the original plug when it is in good shape to keep using it. Otherwise the cord gets replaced with a two prong polarized version. Hard to find in gray though. Thank you for these informative videos. Subscribed.
Hey there, ran across this video in my search on how to properly wire up a vintage television set. This is great information and I am glad to have learned it. Thanks for the video!
Recapping the second 2d30 preamp right now. This one is a little different than the first and the schematic. 2 different capacitors in this one than the schematic has.
Brilliant explanation!! I never thought of its use as a LPF. Capacitive reactance will act as a pseudo-resistor at 60HZ, limiting the current. Still get a nasty jolt, though, under the right conditions. Thanks for posting this video!!!
As a 16 yr old playing guitar on an old Ampeg V4 Guitar Amp, which a previous owner has stupidly pulled the 3rd grounding plug out of to fit into 2 prong outlets, this capacitor saved my life.
Great explanation video. Wouldn't your example at 4:00 however, be putting the hot side right to chassis ground if plugged in that way?? From my experience non polarized plugs were the norm easily into the 60's when a lot of this stuff was made so that means one expected a tingle at the mike then??? All homes etc. would have had outlets that weren't polarized ( mine still does). Or was the expectation to make sure it was plugged in correctly on the user?? I am working on a 1939 GE radio with an AC transformer power supply. It follows your basic amp power supply schematics with a 5y3 rectifier tube. However, it uses a double capacitor connecting both hot and neutral to chassis. It wouldn't matter which way this is plugged in but then typically one isn't touching the chassis on these units. The back is open open with the chassis though. They were covering both sides with a filter as it could be pluggeg in either way????
Excellent video as well as interesting. Great information foremost for safety reasons. Two of my guitar amps are more modern (a 1980 Mesa Boogie Mark IV and a circa 2011 Red Plate Hand Wired amp). However, I do an old Premier Guitar amp from either the early 1960s or earlier, that I thought of fixing and putting back into service one day. It would be safe to assume that amp has a death cap based on what you alluded in this video. (It the Premier model that has a triangular shaped head and triangular shaped speaker cabinet) and they fold and clamp together for transport. Thanks for doing a very detailed video on safety...BTW: I remember getting tons of shocks as a kid playing guitar when your lips touched the microphone. Who knew! Phil NYC Area
Not only the plug can go either way you need to know the socket is wired correctly, just don't assume anything with mains power and keep one hand in you pocket.
The keep one hand in your pocket it some really good advice. I have hurt myself measuring voltage by laying my other hand on a heatsink. I quickly found out there was voltage going through it
Seems the best bet is to buy one of those testers and plug it into the socket before trying the amp! 2 extra minutes could be that life saver you need!
@@tmastersatYes that is true but some plugs are not polarized hence the risk. Most European plugs are not polarized either and they carry 230 v . The UK plug and socket are polarized and each plug is fused as well as circuit breakers but I have seen them wired incorrectly. The new UK system is to have completely sealed plugs so no one can do anything but change a fuse. Just to say if there is a way to screw it up someone will.
Great summary of the purpose and fitting of those filter capacitors. Over here in Europe, many of our countries have symmetrical power outlets and connectors, so here we really have to double check the polarity manually if we have equipment like this. Some countries do have polarised plugs, notably the UK, Ireland and Denmark. A few others do also have asymmetrical contacts. However, not all of those have a standardised polarity order. The many that use the German Schuko style symmetrical connectors have no option but to check for the polarity. I usually try to do that for equipment that do have a marked polarity. It is worth noting though that this has been a known fact for basically ever, and equipment _should_ be designed to work in a safe manner regardless of the polarity of the connected power (not always a given, especially not for homemade or vintage equipment).
great video! new to tube amps and wanting to learn from the right spot. is this part of a series I can start watching? any good book recommendations for someone with ZERO electronics background to work on/repair/maintain tube amps?
My parents kept an old 'All American 5' style AM radio in the kitchen next to the sink. As an inquisitive 5 yr old, I one day pulled a knob off, exposing the metal shaft. Touching the rim of the sink as I leaned over to touch the shaft I got one heck of a shock. I looked at my finger to see if I was OK and was horrified to find my finger tip was 'disfigured' with a bunch of circular marks. This was how I discovered fingerprints.
Thank you, another great informative video! Coming from the guitar amp building world I've removed my fair share of deathcaps and always went with option 2 (I always would offer the removed parts to the customer and usually they didn't want them, and many of them are vintage bumble bees in good values for guitar tone pot cap if they're still good). It's good to know there are other considerations now that I'm delving into audio stuff and #3 looks like a good option for vintage gear.
Mark, FWIW, I have SO many screen shots of pieces and parts of your videos that I feel like I should make a separate folder called “Mark’s Masterpieces”. Your detailed explanations are so very appreciated, and I’m sure I’m not just speaking for myself as far as the appreciation AND screenshots! So glad you seem to be doing better too. There’s a lot of people who care about that southern drawl of yours!
I find it interesting that the EICO HF-85 in your video did not have a fused AC input. I "built" an HF-20 (my first kit that required soldering) in 1959, which HAD a fused line (2A). It was a GREAT 20 watt MONO amp AFTER I had a local "radio/tv shop" (remember those?) fix a "COLD SOLDER" joint for chassis ground! I was using a Weller soldering gun (remember those?), not enough heat for good solder flow. The guy that owned the shop "fixed" my amp for FREE, took him about 5 min to find the "problem". Assembling that kit jump started my carrier as an electronic tech for the next 40+ years!!
Many years ago I had a valve amplifier with a capacitor start for the special motor that it uses. The motor is a German Pappst type with a static stator on the inside of the outer rotor. The capacitors are hard to get hold of now, but having tried electrolytic capacitors and watched them fail, I managed to buy some paper capacitors, which solved the problem. I still have the recorder deck and occasionally run it to keep running it to keep everything going. Paper capacitors are known to fail, if not used from time to time. An electrolytic capacitor failing is very messy as it blows the end of the capacitor off. They do have paper in them but it deteriorates. We know them as leaky capacitors. Geoff G4GNQ.
I have a boat anchor shortwave that I plan on rewiring for a green-wire ground system that doesn't connect its neutral to chassis. It might take a bit of work, but the beast needs a bit of work, anyway.
I agree with others comments - great vid that explains the issues clearly and offers a great example of Y cap use. Plus, gotta love adding a fuse:). Thank you!
I learned early about capacitor discharges. When I was a child I pulled the plug of our family's color TV out of the outlet and touched my tongue to it. It shot a 12" purple arc down to the corner of the floor. After sitting motionless for a few minutes I realized I shouldn't have done that but was fortunate that I didn't hurt myself. I never did it again.
That would have been some 17-35kv stored in the anode of the screen in those old sets, that must have backfed through the AC plug. You became a grounding rod, and something metallic near the floor help dissipate the charge. You're lucky, albeit low amperage in that discharge, definitely not fun getting snapped at with that much potential. 📺⚡👈😲
Years ago my wife had found an old toaster that still worked, but I noticed that it had an old two pronged plug. I knew which way to plug it in, being an electrician, but I replaced the cord with a two pronged polarized plug so it is safe. Now...back in the day it could have electrocuted or given someone a bad shock if it was plugged in wrong AND the person was touching the toaster and say..a metal faucet. They then would have become a path to ground. I hope this scenario helps in understanding the importance of proper grounding.
I have a wiring question about connecting the black(hot) wire first to the fuse then the switch, why not the switch first, then the fuse? An internal fuse holder it is obvious if you're opening up the equipment that you should unplug it... but assuming if you have one of those round external fuse holders so you can replace the fuse easily, If I were to switch off the equipment and then try to change the fuse, I might get a surprise that I wasn't expecting. But I have to ask this, since I am curious, even if it were an internal fuse holder, again, assuming that the switch and fuse are in series to the transformer, what would be the advantage, if any, to wire the fuse be first then the switch? I'm sure there has to be a reason to recommend this order of wiring.
I just purchased a 1936 Philco Model 650 console radio. I checked the schematic and it actually has two 0.015uf death caps. Each leg of the incoming cord has a cap to ground. Of course the pug is original and not polarized, so I guess you could say it’s double death capped? 😬I’m going to try installing a new cord with ground, and remove the cap on the hot leg.
This is why my Dual 1229 euro spec will pop at start and stop.? Actually had a Dual 1218 that the motor would only have enough power to get through the start cycle if the plug was in a certain way. I had one of the plug prongs colored red with a sharpie. Thank you for posting this! Took me 5 years to stumble across it but I knew something weird was going on in these old Dual turntables.
how about replace the death capacitor with a new one so its time to failure is now not so soon and use a gfci circuit to power the unit only. Then if the capacitor fails instead of getting a shock, the gfci will trip instead.
I have a vintage Heathkit solid state amp with 2 .05uf 1400v ceramic death capacitors. I temporarily marked the hot side on the plug. Now I am going to swap out those caps with safety caps per option 3 and install a new cord with a modern 2-prong plug.
Now I know why when I tried to show my dad the old fridge in the basement shocks me bad when I grab the handle, I couldn't prove it! He unplugs it occasionally to de-ice, but that time had plugged it in correctly. Glad I didn't die in my youth. Also I like catching small errors in explanations: If your capacitor shorts, the capacitance does not go to zero but rather opposite. You said do the math with cap going to zero but the math shows that would approach infinite resistance and be fine. Obviously a larger capacitance is what allows more current to pass through at a given frequency.
All excellent information ! I prefer to replace the line cord with a polarized line cord. Would it also be wise to replace this cap with a new one if its over 20 years old?
I am ordering parts to rebuild an HF 85 as you have done. I have been thinking about adding a fuse too, because the transformer was bad and I had to have one made. (Heyboer) The receptacles on mine are cracked and not polarized, I am thinking about removing them and installing blanks from the inside. I would then use a lug strip to make connection. Switched receptacles don't seem to have mush use in today's HiFi.
I'm a little confused. At 6 minutes your schematic shows the death cap between hot and neutral. At 12:05 the schematics show the death cap not going between hot and neutral... rather from one or the other to chassis. Aren't these completely different?
Hi Anthony - your confusion is right. The first schematic shown is actually NOT representative of how a death cap is wired, nor of how it functions. This first schematic is representative of a manner of ‘shorting out’ high-frequency noise by using a capacitor across the feeding lines. A death cap would actually work between the neutral line and chassis ground, again ‘shorting out’ high-frequency noise on the power-line to ‘earth’; this ‘earth’ being represented by the device chassis, in the absence of a real ground reference.
@@petervanvelzen3116 Thanks Peter. Does that mean that if I have an old audio device which is wired like the first schematic, I should not only replace that cap with a safety rated one, but also move it to look like the second schematic?
Great video. Here in Australia, I believe we've always had 3-prong mains outlets. Well since it was codified in the 1930s, anyway. I just can't imagine ever connecting a neutral mains to a chassis. And I don't believe I've ever seen any gear, vintage or otherwise wired that way. AFAIK our plugs, still in use, were copied from a now obsolete (3-prong) American design. I wonder why the US ditched the earth prong?
Another potential issue with grounding the chassis to earth ground is that if the neutral is also bonded to the chassis in any way (signal ground), you’d be violating electrical codes that dictate that neutral and ground can only be bonded in one place in your entire system, usually your breaker panel or your meter base. You’d create a ground loop in your house which isn’t ideal for safety. This is if I understand all this correctly..
I learned this the hard way about plugging in a 2 prong cord...One night I was up very late working on restoring a Jukebox....I forgot that it was still plugged in guess I should of just given up for the day and gone to bed....But I reached down to to pick up the amp and I instantly got lit up and had a death grip on both the amp and the side of the jukebox..I fought it for a long time trying to let go but I couldn't....I started to panic and then a calm just came over me as if I wasn't even being shocked to death anymore....I was able to finally realize I would not be able to let go and that I needed to unplug the Jukebox by dragging it and in doing so I dislocated my shoulder...Always unplug anything you are working on and make sure its grounded and plugged in correctly before touching anything on old equipment with 2 prong chords.
Sorry if you answer this somewhere towards the very end, but, it occurs to me that there is a potentially much better approach: use a safety capacitor to ground between ground and the chassis. That might not technically be code in the US, but obviously neither is doing that from neutral. It presumably is somewhat safer, because it doesn't have potential back current coming from neutral to the area, and for the same reason, it might actually reduce the level of interference that's possible. Since system should be electronically isolated from the transformer, there shouldn't be any particular safety issue from electricity in the device unless something really shorts to the chassis. I would expect it to prevent ground loops at least as much as the pass-through capacitor to neutral would. What do you think about that approach? The only drawback that I could see that I don't think is really a big issue is that you do have to add the three-prong cord to the device still, and, compared to fully grounding the device, it does mean that if something externally electrifies the outside of the box, you have a little bit less safety protection than you would if you fully grounded it. Thoughts?
Blimey, I may moan about our huge three-pin plugs here in the UK, but this video really brought to mind how much safer those plugs are - even with double the voltage of the USA!
I never understood the big deal about the death cap - lots of things would have to go wrong in order for it to kill anyone. First of all if it shorted, it would blow a fuse. If it didn’t do that- it would trip the breaker switch at the panel. If for some reason it was a partial short - it would starve the primary side of the P.T. Of voltage, thus your amp wouldn’t work. Even if it did, the plug in wall would have to be reversed. And if you have no center taps to chassis ground on the secondary side - then it’s effectively an isolation transformer, and nothing will harm you.
Unfortunately, your drawing is wrong. You already have a full 120 volt AC connection to ground ! If the bottom plug prong of your AC plug is inserted into the hot side of the outlet, which is a 50/50 percent possibility (1 out of 2 odds) you already have 120 volts hot on your chassis, mic or guitar regardless of the condition of that capacitor! (See 4:52) The danger of a cross-the-line cap is not a short to ground but a short arose the AC outlet causing a potential fire hazard if the fuse / circuit breaker is slow to burn / trip, respectively.
Thanks for the info , how do you know what side is positive and what is negative on those old capacitors, I have 3 in an old stereo unit that look like the ones in your video ordered 3 new ones from mouser they’re marked pos and neg. Don’t want to put them in wrong. Thanks for the help, jerry
A standard GFCI in the USA trips at about 5mA mismatch of current; the video shows that the capacitor in the example calculation only had about 1/2 of that current flowing. So the standard design is not going to be sufficiently sensitive. But if one were to carefully modify a standard device to increase the sensitivity, one could embed that into an extension cord of some sort, and only power devices with that. Lots of trouble to do that when an easier solution is to just use a polarized plug on the device in the first place.
As we don't have polarised plugs in most parts of Europe, this came to mind: couldn't you instead of filtering RF interference back to the neutral conductor instead filter it off to the protective earth conductor? That way you're not directly connecting the signal ground to earth, but in case the capacitor fails, you'll end up with a bit of extra hum either way regardless how the capacitor fails? And polarisation doesn't then matter at all?
I've been a musician since the 60s and I cannot count the number of times I received a nice jolt thru my lip from a hot mic. That's why most amps back then had a polarity switch on the back.
I don't get it. In the diagram, you have a 2-prong plug, one lead goes to chassis ground. The two leads go on to power supply and a capacitor in parallel. I would think if the capacitor was shorted or leaky, it would either burn or the circuit breaker would trip. How does that give a shock to someone touching the chassis any more than if the capacitor were working perfectly? Likewise if the capacitor were open?
I had my head around this in seconds. The repercussions of death caps is indeed potentially death! Quite scary when you consider some older wax caps etc do often dry out and go short circuit 😱
Never could understand how North American standards allowed electrical plugs and sockets to be made in this way, they should be made irreversible to keep neutral and live in the same orientation.
I always knew about DC electricity and how it worked (enough to make repairs, and little projects and stuff) but had NO idea about AC Line and Neutral, mainly due to these plugs. I thought "polarity" didn't matter whatsoever with AC until I learned more about AC and the system as a whole and said to myself "Wait, what if another device is on the other side of that sine wave?" I thought I was wrong and looked that up, only to see I was right and those cords are old and dangerous.
He is talking about old fashioned plugs. Anything made after about 1975 has the blades different sizes so that you can't plug it in wrong unless you file the wide one down.
The current standard for NEMA-15 (North America - including Mexico & Canada, 110-120v @ 60Hz) has polarized plugs and connectors (one pin slightly wider than the other), as well as those with a third pin for ground. But yeah a lot of old stuff doesn't have it (which really isn't good), as well as plugs for things where polarization isn't supposed to matter. en.wikipedia.org/wiki/NEMA_connector Japan also has a very similar (practically compatible) standard. Not sure what their differences are though.
Now, any advce on a the X cap versus the Y cap approach to minimizing noise? What about using both? Would an X1Y2 set up provide better noise suppression, especiall in a noisy enviornment?
On old amps (music or hi-fi) which use the chassis to complete circuits you really should find those points (ground wires screwed into or soldered to the chassis) and modify them so that they all connect to a "star" ground insulated from the chassis. Then you can use a modern 3 wire plug. Also removing those old style ground points will also eliminate the chance of high voltage getting to the chassis through them in the case of a capacitor failure other than the death cap. The green wire on the plug is really only there in case some high voltage hot wire comes in contact with the chassis due to say a solder connection coming loose on a high voltage line. Removing any part of the amp circuit that uses the chassis as a conductor eliminates even the possibility of high voltage getting to the chassis. Also before you work on any older amp that uses high voltage you should test for high voltage on the chassis using an AC voltmeter in case you have an amp that you've never seen before that may come to you with a high voltage already getting to the chassis for whatever reason (somebody messed up or a wire broke loose-whatever). Also those multiple ground wires to more than one point on the chassis can develop corrosion and cause all kinds of hum due to one ground point being clean and another having resistance due to corrosion or loose connections. I really would never feel safe around an old amp that doesn't have a 3 wire plug and I've been playing and working on tube amps since the sixties. Before I play an old amp I always check for a grounded plug and ask the owner if the death cap has been removed. I know everyone wants to keep things "vintage" but all these mods if done properly could be reversed back to factory if someone insists on keeping an amp in a dangerous config. Personally I wouldn't feel comfortable working on anybody else's equipment if they wanted to keep it in an unsafe config. If that person gets shocked or injured and you worked on the amp you could be liable if you knew the mods should have been made but you didn't do them for whatever reason. My dad started out as a radio tech in the Navy and he always joked that the good high voltage techs were the ones that were still alive. I took that lesson very much to heart. Remember that high voltage is always looking for someone to kill and that's no joke!!
Great informative video. I have a an old Kay 703-C amp. One side of the 2 prong ac goes to the switch but it appears (i’m still learning how to read schematics) to go to an isolation transformer. The iso has a cap as well near it. My question. is that still considered a death cap With the isolation transformer in the circuit? And yes, it is labeled isolation transformer on the schematic.
There is a death cap on my 1980 pioneer sx590 home receiver/tuner/amp. If I do plug it in the incorrect position I can feel the current on the metal parts connected to the chassis. Kinda vibrates your finger or arm when sliding along the metal.
Actually even older, unkeyed power cables have indicators to show which pin goes to neutral. Its the rib or stripe on the wire that goes to neutral IIRC.
I took my NAD 7400 receiver for repair, but the guy is having a hard time finding transitors/capacitors repalcement. Can you suggest a place where to buy those components?
My Kustom Kasino amplifier had a toggle switch on the back to select which "neutral" went through the death cap to chassis! I guess it was to correct for plugging it into the wall backward? I suppose if you heard line noise, you'd flick the switch to whichever position sounded better :| I rewired it with a modern 3-prong plug-end cord AND installed a line filter module inside the chassis. I left the toggle switch there but not connected to anything. Any future owner of the amp can play with it all they want ;)
This is scary. I remember playing shows when I was younger. At certain venues we would get shocked bad when coming close to the mic. Some amps have a ground lift button that you can activate which in some cases seemed to help.
Hello thank you for your video. I have a bad capacitor on my old sewing machine on the motor with rating 0.1nF + 2x 2500pF. It is hard to find new with same rating. Any help on how to replace it? Thank you
Would a large diode on the neutral side of the cap stop the current flow if the cap fails? Or Maybe some other device that opens if the cap fails short?
Hmmmm - TV sets have cabinets that protect fallers. The cathode ray tube's 25K anode voltage connections are insulated. The 25K in one arm won't kill you (I've proved that by accident several times.) 25K in one arm won't restart your heart
I had a vintage stereo receiver from the 60s that began shocking me when i touched certain areas of it. Anyway, i was too scared to use it anymore and unplugged it. Don't know why it started to do that because the unit appeared to be in good condition.
Wait... if we simplify the scenario by removing the fuse the cord from the equation (assume it's already been replaced with a polarized one), we just need to remove the death cap and replace it with an X/Y safety capacitor? Example: My radio has the death cap coming from the 35Z5-GT pin 5 to ground. So, do I just replace it with an X1/Y2 safety cap and that solves the problem?
charles tim edwards thats because the earthed cords are cheaper than the 2-wire keyed type, they simply leave the ground floating with respect to the chassis.
@@HighestRank Plus you can't plug them in the wrong way, so it eliminates at least one random element, and that tester would eliminate the other one, ie house wiring being ass backwards. They likely don't hook up the earth. Though this video has me wondering why they don't put a regular death cap to the earth pin, so if it fails you get the hum but not the death.
Thx for sharing. Death caps who new. Seems like a lot of the old equipment was just built not engineered with safety in mind. Strain reliving the power cord or any cable that penetrates a metal chassis is the bare basics of construction. Nice to know how to upgrade the older equipment so that they can still be enjoyed without killing their owners. These vintage amps sounded too sweet to be killing their owners. If folks follow the recipes in your video no one has to worry about noise and safety. Good job.
According to my Dad (not a good source of knowledge) they built things like that because people back then knew enough to NOT stick their hands in there!! Nowadays, you'd have to have safety stickers all OVER it!!!
Thank you Mark. You are the only one, among many, that has dealt with this issue in a professional and code compliant sense (although some jurisdictions require a earth-ground metal chassis regardless of what other measures are in place). First priority is safety. Hums / ground loops are secondary to be dealt with separately. I used to build custom control systems which required a 'special' inspection /approval process by the local electrical authority. Not only did the Hammond metal cabinet require an earth ground but the door had to be electrically bonded to it even though it too was metal with a metal "piano" hinge and it had to be tied with ring terminals. No spade connectors allowed. The neutral is NEVER switched alone including fusing. I
Thanks again for this.
Finally, a video that covers the topic well and discusses all the decent options. Now I can point folks (customers) here to educate themselves. Thanks Mark. Well done.
Finally someone explained the death capacitor in a way I could understand. Thank you for the great video.
I have a fender twin reverb guitar amplifier. I threw away the two prong cable and installed a three prong one. I grounded the cable at the base of the power supply transformer and cut out the dearh capacitor. No problems since then. Better safe than sorry! Nice video!
Thank you so much for this. I have a basic background in theory from my electrical apprenticeship and the way this is all presented makes perfect sense to me. This will be the video I send to other people to explain the concept. I filled in a ton of gaps with this thanks.
Thank you.
As a chemist, I had to work on older equipment. The electronics people helped me deal with death capacitors and other safety issues.
Thanks again. Happy New Year.
At first I thought this was about old paper type capacitors that fail, start passing current and destroying electronic parts but now I see its about the equipment trying to kill people.
Years ago we had a lot of old tube amps for my brothers band and you had to pay attention how things were plugged in. One time I watched my brother step up to microphone and get big blue flash right in his lip
My first live performance in 1966, I had a tiny amp for a mic and another tiny amp for my guitar. As soon as my lips touched the mic, I was almost knocked out and my face was uncomfortably numb for about a half-hour. It took me another 30 years before I was able to shake my mic shyness.
"Hot" chassis in tube radios was quite common up into the 1950's. My father taught me how to properly orient the plug using an NE-51 neon bulb with a resistor.
Televisions were worse, they didn't have a mains isolating transformer and one side of the mains went directly to the chassis.
@@rogerbarton497 That is just what hot chassis radios did.
I could never understand why those old AC plugs were NOT polarized!
The capacitor layouts may be common to audio amplifiers but transceivers (two way radios) almost always have at a bare minimum a cap from hot to chassis ground and one from neutral to chassis ground. For this application some vintage tube radios used a (popular at the time) very large ceramic disc capacitor that had 3 terminals. It was basically two capacitors in one ceramic capacitor package. Some radios used a 3 capacitor layout. The two mentioned above and another across the hot and neutral. In solid state units that did not have a 3 prong earth ground type cord it is also common to have a high resistance resistor tied from the common line to the chassis for a earth reference. In ANY radio and I mean ANY vintage radio be it solid state or vacuum tube type always replace all these capacitors. The ceramic types fail just like old paper caps did. Only difference is they dont slowly short out over time. They go from working perfectly to dead short. They are attached to the mains any time the cord is plugged in and get the snot beat out of them by power line surges. I have seen several dozens of them that have exploded over the years. One that even caught the radio on fire when it shorted out in a Tram D201 CB radio. When it shorted out near the power transformer it caught the transformer insulation paper on fire.
You can find modern x1 y2 rated capacitors from almost all the large electronic supply companies like DigiKey, Allied, Houser, Newark, etc. Most of the time the problem is people have a hard time finding them on their websites because they don't know what ratings to search for. A good source if you work on tube gear is www.justradios.com . David and Babylyn have a simple to navigate website and sell these capacitors. All the capacitors they sell are on one large page. They specialize in repair parts for tube gear.
Thank you.
MikesRadioRepair I use 57-63 valve amps .. my fave being a 63 amped vt40. I use these amps regularly... probably should change some caps😂👍
Great job ! I understood all of that. I especially appreciate the information regarding the different recommended approaches for handling a vintage guitar amp versus a vintage piece of audio gear, since I own both. Than you very much.
We put capacitors in line on our fishing electonics for " noise" suppression.
Interesting topic.
Thank you for passing on your knowledge and wisdom.
Greetings. As the author of the "infamous" Death Cap video referenced in your presentation, I feel obligated to offer some insights. 1.) The video was created 6 years ago and is somewhat simplistic in its approach, as was my understanding at the time, but it was an honest attempt to bypass the hysteria and factually evaluate "Death Capacitors" in circuit. 2.) I use the rather imprecise term "hum" to cover all extraneous noise which could enter the circuit via the primary wiring. 3.) To be more thorough, I should have reversed the AC plug and repeated the voltage and current measurements, but at no time would plug reversal ever result in "full AC voltage to the chassis" of any of the amplifiers. 4.) That said, my observations were based on the data at hand, rather than hearsay, and were offered as opinion.....to affect the handling of the vintage amps in my own collection, which I preferred to keep in original condition if possible. In the one case where the "Death Cap" demonstrated current flow to the chassis, it was removed.
I personally see no issues with the conclusions and would caution people to recognize that opinion is not fact, regardless of whose opinion it is, and when opinion does not agree with your preconceived notions, it is not necessarily wrong.
I enjoyed your video and found it to be quite thorough and well presented. You offer logical choices for the prevention of shock hazards and ground loops, which prove helpful to many viewers. Thanks for posting it.
Hello Uncle Doug. Didn't mean to stir up anything with that portion of my video, I just kept running across sites that quoted it as being flawed when I was making this video. As I mentioned, sadly I hadn't watched your video so in fairness, I probably shouldn't have posted that. I have the utmost respect for you and what you do.
I did find it a bit strange that you would take the time to cite my video as being flawed, especially since you had never watched it, but no doubt all videos that express opinions.....and all do.....are flawed to those whose opinion differs. Regardless, I found the portion of your video that was dedicated to the topic to be factual and very well done. Thank you for your effort in that regard.
@@UncleDoug I find it refreshing that you are owning up to any mistakes that may have been made. I also haven't watched your video on the topic, but I might have a look since I am studying up on the subject at the moment.
May I ask, if there was indeed "not quite right" I guess you could say, information in that video, has it been amended to reflect the new information? Not to offend, just that if it was me, I would have made a change or two rather than leave it up. But as I said, I haven't watched it yet, you may have done this already. And yes, sadly when it comes to electronics, there can be different interpretations of the same basic knowledge unfortunately. I'm sure the majority of your info is more than solid. I will take a look in the morning and most likely subscribe to you as well! So great to have some actual experienced minds to watch and learn from!
@@ballsrgrossnugly The video was not amended......there is no means to do so, MM.......and I still feel that it served a valid purpose. I never said that it was "not quite right", but could have been more thorough......let's face it, so could virtually all such videos. It is still my contention that an intact "death capacitor" in an amp with a properly installed 3-wire chassis-grounding power cable is a non-issue.
@@UncleDoug Still awake lol maybe I should just watch the damn video instead of assuming huh?
Yeah the way you explain it, it's at least not a safety issue. Maybe a buzz issue but that's not the point of a safety warning. Fair enough. I'll watch that video rather than comment any more and securely place my toes down my own throat!
Thank you, Mark. This is no joke at all. I got a huge zap from plugging my guitar into an old vintage Marshall amplifier that was in for repair at my buddy’s shop. The second l touched the strings, I thought my friend had run full speed across the shop and jammed his elbow between my shoulder blades or slammed me in the back with a baseball bat! It felt like a truck had hit me. He of course didn’t do that, but a big zap is a very scary thing that you don’t forget. This happened to me around 25 yrs ago.
I am of course extra careful when I am poking around inside any gear since then, whatever it may. Use a chopstick to check around and keep one hand in your pocket.
ZZzap...those old vacuum tube amps had 300-400 volts all over the place...
same here, a Fender Quad reverb. I was standing up playing through the amp and for some reason I reached over to switch channels on a small TV and that's when a giant hand picked me up and threw me Gainst a wall, scared the living crud outvof me and taught me to double check all Earth/ground wires on ",Everything and to use a "Discreet" socket just to power my Guitar amp and nothing else, nastyvnasty shock!
@@dougankrum3328 Felt more like a cannon blast straight to the head.
@@GiulioLuzzardi-xf1xo Yeah, it’s brutal.
Very good video lesson. Learned a long time ago that the caps didn't fail in the user's favor. Especially the radios with direct line-to-tube rectifier sets. All of my Heathkit equipment so far has had the two fat HV disc capacitors on both legs of the line cord to chassis. Wired as if they were safety caps. They are not! I always replace them with two X1Y2 safety caps and mark the neutral lead on the original plug when it is in good shape to keep using it. Otherwise the cord gets replaced with a two prong polarized version. Hard to find in gray though. Thank you for these informative videos. Subscribed.
Hey there, ran across this video in my search on how to properly wire up a vintage television set. This is great information and I am glad to have learned it. Thanks for the video!
Very good explanation Mark and I learned much from you today.
Have a Blessed Week.
Thanks Mark! love your instructional/educational videos. I've seen others replace this circuit but now I understand why.
Thank you! I am about to rebuild a couple of Zenith 7d30 chassis and was going to research how do this. Perfect timing! Thanks again.
Recapping the second 2d30 preamp right now. This one is a little different than the first and the schematic. 2 different capacitors in this one than the schematic has.
Brilliant explanation!!
I never thought of its use as a LPF. Capacitive reactance will act as a pseudo-resistor at 60HZ, limiting the current.
Still get a nasty jolt, though, under the right conditions.
Thanks for posting this video!!!
Thank you Mark! Great information and clearly presented!
Your channel is simply amazing. I feel like you are my personal instructor on tube electronics. There aren't many people in my area to learn from
Thanks for the video! What I took away from this: I don't want to ever use old vintage gear to listen to music.
As a 16 yr old playing guitar on an old Ampeg V4 Guitar Amp, which a previous owner has stupidly pulled the 3rd grounding plug out of to fit into 2 prong outlets, this capacitor saved my life.
Great explanation video. Wouldn't your example at 4:00 however, be putting the hot side right to chassis ground if plugged in that way?? From my experience non polarized plugs were the norm easily into the 60's when a lot of this stuff was made so that means one expected a tingle at the mike then??? All homes etc. would have had outlets that weren't polarized ( mine still does). Or was the expectation to make sure it was plugged in correctly on the user??
I am working on a 1939 GE radio with an AC transformer power supply. It follows your basic amp power supply schematics with a 5y3 rectifier tube. However, it uses a double capacitor connecting both hot and neutral to chassis. It wouldn't matter which way this is plugged in but then typically one isn't touching the chassis on these units. The back is open open with the chassis though. They were covering both sides with a filter as it could be pluggeg in either way????
Excellent video as well as interesting. Great information foremost for safety reasons. Two of my guitar amps are more modern (a 1980 Mesa Boogie Mark IV and a circa 2011 Red Plate Hand Wired amp).
However, I do an old Premier Guitar amp from either the early 1960s or earlier, that I thought of fixing and putting back into service one day. It would be safe to assume that amp has a death cap based on what you alluded in this video. (It the Premier model that has a triangular shaped head and triangular shaped speaker cabinet) and they fold and clamp together for transport.
Thanks for doing a very detailed video on safety...BTW: I remember getting tons of shocks as a kid playing guitar when your lips touched the microphone. Who knew!
Phil
NYC Area
So, just plugging in and trying to use old audio equipment can kill you unknowingly. Scary stuff given how retro has really made a resurgence.
Not only the plug can go either way you need to know the socket is wired correctly, just don't assume anything with mains power and keep one hand in you pocket.
The keep one hand in your pocket it some really good advice. I have hurt myself measuring voltage by laying my other hand on a heatsink. I quickly found out there was voltage going through it
Seems the best bet is to buy one of those testers and plug it into the socket before trying the amp! 2 extra minutes could be that life saver you need!
@@alien_man1669 The rule is; one hand in your pocket if you know what you're doing, both hands in your pocket if you don't know what you're doing. :)
They were polarised you could not plug it in the wrong way....one side os larger
@@tmastersatYes that is true but some plugs are not polarized hence the risk. Most European plugs are not polarized either and they carry 230 v . The UK plug and socket are polarized and each plug is fused as well as circuit breakers but I have seen them wired incorrectly. The new UK system is to have completely sealed plugs so no one can do anything but change a fuse.
Just to say if there is a way to screw it up someone will.
Very informative. Now I understand what is a low frequency filter!
Now I understand after all these years! Thank you!
Great summary of the purpose and fitting of those filter capacitors.
Over here in Europe, many of our countries have symmetrical power outlets and connectors, so here we really have to double check the polarity manually if we have equipment like this. Some countries do have polarised plugs, notably the UK, Ireland and Denmark. A few others do also have asymmetrical contacts. However, not all of those have a standardised polarity order. The many that use the German Schuko style symmetrical connectors have no option but to check for the polarity. I usually try to do that for equipment that do have a marked polarity. It is worth noting though that this has been a known fact for basically ever, and equipment _should_ be designed to work in a safe manner regardless of the polarity of the connected power (not always a given, especially not for homemade or vintage equipment).
Very good video explaining a possible dangerous situation. Thank you again for the videos Mark!
great video! new to tube amps and wanting to learn from the right spot. is this part of a series I can start watching? any good book recommendations for someone with ZERO electronics background to work on/repair/maintain tube amps?
Me too!! All I can afford is the "it lights up, but..." tube radios online (or told it works, but doesn't)...
DE KE8NFK
(Carson's Lab): has posted videos here doesn't advocate attachment a ground wire to the chassis either.
My parents kept an old 'All American 5' style AM radio in the kitchen next to the sink. As an inquisitive 5 yr old, I one day pulled a knob off, exposing the metal shaft. Touching the rim of the sink as I leaned over to touch the shaft I got one heck of a shock. I looked at my finger to see if I was OK and was horrified to find my finger tip was 'disfigured' with a bunch of circular marks.
This was how I discovered fingerprints.
Thank you, another great informative video! Coming from the guitar amp building world I've removed my fair share of deathcaps and always went with option 2 (I always would offer the removed parts to the customer and usually they didn't want them, and many of them are vintage bumble bees in good values for guitar tone pot cap if they're still good). It's good to know there are other considerations now that I'm delving into audio stuff and #3 looks like a good option for vintage gear.
Mark, FWIW, I have SO many screen shots of pieces and parts of your videos that I feel like I should make a separate folder called “Mark’s Masterpieces”. Your detailed explanations are so very appreciated, and I’m sure I’m not just speaking for myself as far as the appreciation AND screenshots!
So glad you seem to be doing better too. There’s a lot of people who care about that southern drawl of yours!
I find it interesting that the EICO HF-85 in your video did not have a fused AC input. I "built" an HF-20 (my first kit that required soldering) in 1959, which HAD a fused line (2A). It was a GREAT 20 watt MONO amp AFTER I had a local "radio/tv shop" (remember those?) fix a "COLD SOLDER" joint for chassis ground! I was using a Weller soldering gun (remember those?), not enough heat for good solder flow. The guy that owned the shop "fixed" my amp for FREE, took him about 5 min to find the "problem". Assembling that kit jump started my carrier as an electronic tech for the next 40+ years!!
Many years ago I had a valve amplifier with a capacitor start for the special motor that it uses. The motor is a German Pappst type with a static stator on the inside of the outer rotor. The capacitors are hard to get hold of now, but having tried electrolytic capacitors and watched them fail, I managed to buy some paper capacitors, which solved the problem. I still have the recorder deck and occasionally run it to keep running it to keep everything going. Paper capacitors are known to fail, if not used from time to time. An electrolytic capacitor failing is very messy as it blows the end of the capacitor off. They do have paper in them but it deteriorates. We know them as leaky capacitors.
Geoff G4GNQ.
Thanks Mark! Just the kind of depth I was looking for. Also, hope you are feeling better.
I have a boat anchor shortwave that I plan on rewiring for a green-wire ground system that doesn't connect its neutral to chassis. It might take a bit of work, but the beast needs a bit of work, anyway.
I may have missed it, but i didn't hear you mention what size fuse you installed.
I agree with others comments - great vid that explains the issues clearly and offers a great example of Y cap use. Plus, gotta love adding a fuse:). Thank you!
I learned early about capacitor discharges. When I was a child I pulled the plug of our family's color TV out of the outlet and touched my tongue to it. It shot a 12" purple arc down to the corner of the floor. After sitting motionless for a few minutes I realized I shouldn't have done that but was fortunate that I didn't hurt myself. I never did it again.
That would have been some 17-35kv stored in the anode of the screen in those old sets, that must have backfed through the AC plug. You became a grounding rod, and something metallic near the floor help dissipate the charge. You're lucky, albeit low amperage in that discharge, definitely not fun getting snapped at with that much potential.
📺⚡👈😲
Years ago my wife had found an old toaster that still worked, but I noticed that it had an old two pronged plug. I knew which way to plug it in, being an electrician, but I replaced the cord with a two pronged polarized plug so it is safe. Now...back in the day it could have electrocuted or given someone a bad shock if it was plugged in wrong AND the person was touching the toaster and say..a metal faucet. They then would have become a path to ground. I hope this scenario helps in understanding the importance of proper grounding.
I have a wiring question about connecting the black(hot) wire first to the fuse then the switch, why not the switch first, then the fuse? An internal fuse holder it is obvious if you're opening up the equipment that you should unplug it... but assuming if you have one of those round external fuse holders so you can replace the fuse easily, If I were to switch off the equipment and then try to change the fuse, I might get a surprise that I wasn't expecting. But I have to ask this, since I am curious, even if it were an internal fuse holder, again, assuming that the switch and fuse are in series to the transformer, what would be the advantage, if any, to wire the fuse be first then the switch? I'm sure there has to be a reason to recommend this order of wiring.
I just purchased a 1936 Philco Model 650 console radio. I checked the schematic and it actually has two 0.015uf death caps. Each leg of the incoming cord has a cap to ground. Of course the pug is original and not polarized, so I guess you could say it’s double death capped? 😬I’m going to try installing a new cord with ground, and remove the cap on the hot leg.
This is why my Dual 1229 euro spec will pop at start and stop.? Actually had a Dual 1218 that the motor would only have enough power to get through the start cycle if the plug was in a certain way. I had one of the plug prongs colored red with a sharpie. Thank you for posting this! Took me 5 years to stumble across it but I knew something weird was going on in these old Dual turntables.
Just discovered this channel. Very informative and clear explanations!
how about replace the death capacitor with a new one so its time to failure is now not so soon and use a gfci circuit to power the unit only. Then if the capacitor fails instead of getting a shock, the gfci will trip instead.
I have a vintage Heathkit solid state amp with 2 .05uf 1400v ceramic death capacitors. I temporarily marked the hot side on the plug. Now I am going to swap out those caps with safety caps per option 3 and install a new cord with a modern 2-prong plug.
Now I know why when I tried to show my dad the old fridge in the basement shocks me bad when I grab the handle, I couldn't prove it! He unplugs it occasionally to de-ice, but that time had plugged it in correctly. Glad I didn't die in my youth.
Also I like catching small errors in explanations: If your capacitor shorts, the capacitance does not go to zero but rather opposite. You said do the math with cap going to zero but the math shows that would approach infinite resistance and be fine. Obviously a larger capacitance is what allows more current to pass through at a given frequency.
All excellent information ! I prefer to replace the line cord with a polarized line cord. Would it also be wise to replace this cap with a new one if its over 20 years old?
I am ordering parts to rebuild an HF 85 as you have done. I have been thinking about adding a fuse too, because the transformer was bad and I had to have one made. (Heyboer) The receptacles on mine are cracked and not polarized, I am thinking about removing them and installing blanks from the inside. I would then use a lug strip to make connection. Switched receptacles don't seem to have mush use in today's HiFi.
I'm a little confused. At 6 minutes your schematic shows the death cap between hot and neutral. At 12:05 the schematics show the death cap not going between hot and neutral... rather from one or the other to chassis. Aren't these completely different?
Hi Anthony - your confusion is right. The first schematic shown is actually NOT representative of how a death cap is wired, nor of how it functions. This first schematic is representative of a manner of ‘shorting out’ high-frequency noise by using a capacitor across the feeding lines. A death cap would actually work between the neutral line and chassis ground, again ‘shorting out’ high-frequency noise on the power-line to ‘earth’; this ‘earth’ being represented by the device chassis, in the absence of a real ground reference.
@@petervanvelzen3116 Thanks Peter. Does that mean that if I have an old audio device which is wired like the first schematic, I should not only replace that cap with a safety rated one, but also move it to look like the second schematic?
Great video. Here in Australia, I believe we've always had 3-prong mains outlets. Well since it was codified in the 1930s, anyway. I just can't imagine ever connecting a neutral mains to a chassis. And I don't believe I've ever seen any gear, vintage or otherwise wired that way. AFAIK our plugs, still in use, were copied from a now obsolete (3-prong) American design. I wonder why the US ditched the earth prong?
Great video. Are the two outlets on the back polarized? Why not just disconnect them?
They are not, best not to ever use these jacks in gear.
Just as well, the switched outlet now is fused.
Great video,wondering if you could share the part number of the XY cap,thanks!
Ones I use are www.mouser.com/ProductDetail/Murata-Electronics/DE2E3KY332MA3BM02F?qs=sGAEpiMZZMukHu%252BjC5l7YQoLfzExQCX5T2uhDrRHizU%3D
Another potential issue with grounding the chassis to earth ground is that if the neutral is also bonded to the chassis in any way (signal ground), you’d be violating electrical codes that dictate that neutral and ground can only be bonded in one place in your entire system, usually your breaker panel or your meter base. You’d create a ground loop in your house which isn’t ideal for safety.
This is if I understand all this correctly..
I learned this the hard way about plugging in a 2 prong cord...One night I was up very late working on restoring a Jukebox....I forgot that it was still plugged in guess I should of just given up for the day and gone to bed....But I reached down to to pick up the amp and I instantly got lit up and had a death grip on both the amp and the side of the jukebox..I fought it for a long time trying to let go but I couldn't....I started to panic and then a calm just came over me as if I wasn't even being shocked to death anymore....I was able to finally realize I would not be able to let go and that I needed to unplug the Jukebox by dragging it and in doing so I dislocated my shoulder...Always unplug anything you are working on and make sure its grounded and plugged in correctly before touching anything on old equipment with 2 prong chords.
Sorry if you answer this somewhere towards the very end, but, it occurs to me that there is a potentially much better approach: use a safety capacitor to ground between ground and the chassis. That might not technically be code in the US, but obviously neither is doing that from neutral. It presumably is somewhat safer, because it doesn't have potential back current coming from neutral to the area, and for the same reason, it might actually reduce the level of interference that's possible. Since system should be electronically isolated from the transformer, there shouldn't be any particular safety issue from electricity in the device unless something really shorts to the chassis. I would expect it to prevent ground loops at least as much as the pass-through capacitor to neutral would.
What do you think about that approach? The only drawback that I could see that I don't think is really a big issue is that you do have to add the three-prong cord to the device still, and, compared to fully grounding the device, it does mean that if something externally electrifies the outside of the box, you have a little bit less safety protection than you would if you fully grounded it.
Thoughts?
Great video Mark. Hope you're feeling better. Take care.
Blimey, I may moan about our huge three-pin plugs here in the UK, but this video really brought to mind how much safer those plugs are - even with double the voltage of the USA!
Will using an GFCI outlet to power your amp eliminate the risk associated with the death cap issue.
Good question......no comments
I never understood the big deal about the death cap - lots of things would have to go wrong in order for it to kill anyone. First of all if it shorted, it would blow a fuse. If it didn’t do that- it would trip the breaker switch at the panel. If for some reason it was a partial short - it would starve the primary side of the P.T. Of voltage, thus your amp wouldn’t work. Even if it did, the plug in wall would have to be reversed. And if you have no center taps to chassis ground on the secondary side - then it’s effectively an isolation transformer, and nothing will harm you.
Unfortunately, your drawing is wrong. You already have a full 120 volt AC connection to ground ! If the bottom plug prong of your AC plug is inserted into the hot side of the outlet, which is a 50/50 percent possibility (1 out of 2 odds) you already have 120 volts hot on your chassis, mic or guitar regardless of the condition of that capacitor! (See 4:52) The danger of a cross-the-line cap is not a short to ground but a short arose the AC outlet causing a potential fire hazard if the fuse / circuit breaker is slow to burn / trip, respectively.
Thanks for the info , how do you know what side is positive and what is negative on those old capacitors, I have 3 in an old stereo unit that look like the ones in your video ordered 3 new ones from mouser they’re marked pos and neg. Don’t want to put them in wrong. Thanks for the help, jerry
Would plugging in to a gfci help make it safer?
A standard GFCI in the USA trips at about 5mA mismatch of current; the video shows that the capacitor in the example calculation only had about 1/2 of that current flowing.
So the standard design is not going to be sufficiently sensitive. But if one were to carefully modify a standard device to increase the sensitivity, one could embed that into an extension cord of some sort, and only power devices with that.
Lots of trouble to do that when an easier solution is to just use a polarized plug on the device in the first place.
As we don't have polarised plugs in most parts of Europe, this came to mind: couldn't you instead of filtering RF interference back to the neutral conductor instead filter it off to the protective earth conductor? That way you're not directly connecting the signal ground to earth, but in case the capacitor fails, you'll end up with a bit of extra hum either way regardless how the capacitor fails? And polarisation doesn't then matter at all?
If you decide to ground the equipment you can connect the filter cap between live and neutral, that's what modern amp manufacturers do.
What is a good all around cap to use replacing the death cap. Orange drop?
I've been a musician since the 60s and I cannot count the number of times I received a nice jolt thru my lip from a hot mic. That's why most amps back then had a polarity switch on the back.
What about the polarity switch on many music amps that switches the AC polarity to kill hum? Wouldn't that toggle select dangerous polarity?
Excellent video and well presented. Thank you.😊
Great video. Commentary, a little theory then application on the bench. Thank you.
I don't get it. In the diagram, you have a 2-prong plug, one lead goes to chassis ground. The two leads go on to power supply and a capacitor in parallel. I would think if the capacitor was shorted or leaky, it would either burn or the circuit breaker would trip. How does that give a shock to someone touching the chassis any more than if the capacitor were working perfectly? Likewise if the capacitor were open?
I had my head around this in seconds. The repercussions of death caps is indeed potentially death! Quite scary when you consider some older wax caps etc do often dry out and go short circuit 😱
Never could understand how North American standards allowed electrical plugs and sockets to be made in this way, they should be made irreversible to keep neutral and live in the same orientation.
I always knew about DC electricity and how it worked (enough to make repairs, and little projects and stuff) but had NO idea about AC Line and Neutral, mainly due to these plugs. I thought "polarity" didn't matter whatsoever with AC until I learned more about AC and the system as a whole and said to myself "Wait, what if another device is on the other side of that sine wave?" I thought I was wrong and looked that up, only to see I was right and those cords are old and dangerous.
Here in Australia the plug only goes in one way...
He is talking about old fashioned plugs. Anything made after about 1975 has the blades different sizes so that you can't plug it in wrong unless you file the wide one down.
The current standard for NEMA-15 (North America - including Mexico & Canada, 110-120v @ 60Hz) has polarized plugs and connectors (one pin slightly wider than the other), as well as those with a third pin for ground. But yeah a lot of old stuff doesn't have it (which really isn't good), as well as plugs for things where polarization isn't supposed to matter.
en.wikipedia.org/wiki/NEMA_connector
Japan also has a very similar (practically compatible) standard. Not sure what their differences are though.
Nothing beats the British plug. It's a work of genius.
Now, any advce on a the X cap versus the Y cap approach to minimizing noise? What about using both? Would an X1Y2 set up provide better noise suppression, especiall in a noisy enviornment?
😆 we worked with Capacitors made in Beer Barrells on major aerial sites! Packed a heavy punch for sure 😝 Happy days 😆
On old amps (music or hi-fi) which use the chassis to complete circuits you really should find those points (ground wires screwed into or soldered to the chassis) and modify them so that they all connect to a "star" ground insulated from the chassis. Then you can use a modern 3 wire plug. Also removing those old style ground points will also eliminate the chance of high voltage getting to the chassis through them in the case of a capacitor failure other than the death cap. The green wire on the plug is really only there in case some high voltage hot wire comes in contact with the chassis due to say a solder connection coming loose on a high voltage line. Removing any part of the amp circuit that uses the chassis as a conductor eliminates even the possibility of high voltage getting to the chassis. Also before you work on any older amp that uses high voltage you should test for high voltage on the chassis using an AC voltmeter in case you have an amp that you've never seen before that may come to you with a high voltage already getting to the chassis for whatever reason (somebody messed up or a wire broke loose-whatever). Also those multiple ground wires to more than one point on the chassis can develop corrosion and cause all kinds of hum due to one ground point being clean and another having resistance due to corrosion or loose connections. I really would never feel safe around an old amp that doesn't have a 3 wire plug and I've been playing and working on tube amps since the sixties. Before I play an old amp I always check for a grounded plug and ask the owner if the death cap has been removed. I know everyone wants to keep things "vintage" but all these mods if done properly could be reversed back to factory if someone insists on keeping an amp in a dangerous config. Personally I wouldn't feel comfortable working on anybody else's equipment if they wanted to keep it in an unsafe config. If that person gets shocked or injured and you worked on the amp you could be liable if you knew the mods should have been made but you didn't do them for whatever reason. My dad started out as a radio tech in the Navy and he always joked that the good high voltage techs were the ones that were still alive. I took that lesson very much to heart. Remember that high voltage is always looking for someone to kill and that's no joke!!
Great video. Thank you.
Great informative video. I have a an old Kay 703-C amp. One side of the 2 prong ac goes to the switch but it appears (i’m still learning how to read schematics) to go to an isolation transformer. The iso has a cap as well near it. My question. is that still considered a death cap With the isolation transformer in the circuit? And yes, it is labeled isolation transformer on the schematic.
There is a death cap on my 1980 pioneer sx590 home receiver/tuner/amp. If I do plug it in the incorrect position I can feel the current on the metal parts connected to the chassis. Kinda vibrates your finger or arm when sliding along the metal.
This problem does not affect equipment designed for the uk market if fitted with a 3 pin plug with chassis connected to the cpc.
Fix the pin 1 problem and proper grounding scheme will work. If there are ground loop issues, fix them.
Actually even older, unkeyed power cables have indicators to show which pin goes to neutral. Its the rib or stripe on the wire that goes to neutral IIRC.
I took my NAD 7400 receiver for repair, but the guy is having a hard time finding transitors/capacitors repalcement. Can you suggest a place where to buy those components?
My Kustom Kasino amplifier had a toggle switch on the back to select which "neutral" went through the death cap to chassis! I guess it was to correct for plugging it into the wall backward? I suppose if you heard line noise, you'd flick the switch to whichever position sounded better :|
I rewired it with a modern 3-prong plug-end cord AND installed a line filter module inside the chassis. I left the toggle switch there but not connected to anything. Any future owner of the amp can play with it all they want ;)
This is scary. I remember playing shows when I was younger. At certain venues we would get shocked bad when coming close to the mic. Some amps have a ground lift button that you can activate which in some cases seemed to help.
A foam windscreen on the mic can also keep your lips insulated for addressing the mic while holding a guitar.
Hello thank you for your video.
I have a bad capacitor on my old sewing machine on the motor with rating
0.1nF + 2x 2500pF. It is hard to find new with same rating. Any help on
how to replace it? Thank you
Would a large diode on the neutral side of the cap stop the current flow if the cap fails? Or Maybe some other device that opens if the cap fails short?
I thought it was going to be about a charged capacitor discharging through you. Interesting.
True story.
Man has heart attack
Falls into his tube tv set
Gets electrocuted and lives
Doc says the shock reset his heart ryythm
He now lives a life of fame and glamour. Meets so many women, and during sex, they light up like a pinball machine and give back change.
🙌⚡💡💡 👌😁
I read it on the internet so I know it's true!
Hmmmm - TV sets have cabinets that protect fallers.
The cathode ray tube's 25K anode voltage connections are insulated.
The 25K in one arm won't kill you (I've proved that by accident several times.)
25K in one arm won't restart your heart
@@THEQueeferSutherland if you look it was in several newspapers and he did several talk show rounds
At 12:18 the transformer, the variable resistor and the cap failing all look potentially problematic. Fuse please.
I had a vintage stereo receiver from the 60s that began shocking me when i touched certain areas of it. Anyway, i was too scared to use it anymore and unplugged it. Don't know why it started to do that because the unit appeared to be in good condition.
Wait... if we simplify the scenario by removing the fuse the cord from the equation (assume it's already been replaced with a polarized one), we just need to remove the death cap and replace it with an X/Y safety capacitor? Example: My radio has the death cap coming from the 35Z5-GT pin 5 to ground. So, do I just replace it with an X1/Y2 safety cap and that solves the problem?
You should add text to the vid for the fuse rating.
I'm glad we have safety capacitors now.
I'm seeing most vintage restoration techs changing to a three prong AC cord.
charles tim edwards thats because the earthed cords are cheaper than the 2-wire keyed type, they simply leave the ground floating with respect to the chassis.
@@HighestRank yes true.
@@HighestRank Plus you can't plug them in the wrong way, so it eliminates at least one random element, and that tester would eliminate the other one, ie house wiring being ass backwards. They likely don't hook up the earth. Though this video has me wondering why they don't put a regular death cap to the earth pin, so if it fails you get the hum but not the death.
Why not series fuse the filter capacitor?
Thx for sharing. Death caps who new. Seems like a lot of the old equipment was just built not engineered with safety in mind. Strain reliving the power cord or any cable that penetrates a metal chassis is the bare basics of construction.
Nice to know how to upgrade the older equipment so that they can still be enjoyed without killing their owners. These vintage amps sounded too sweet to be killing their owners.
If folks follow the recipes in your video no one has to worry about noise and safety. Good job.
According to my Dad (not a good source of knowledge) they built things like that because people back then knew enough to NOT stick their hands in there!! Nowadays, you'd have to have safety stickers all OVER it!!!