High Voltage Vacuum Tube Electrolytic Capacitor Discharge Probe / Tool - BG074
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- เผยแพร่เมื่อ 26 มิ.ย. 2024
- Building a tool useful for discharging capacitors of any nature but really effective for those high voltage capacitors found in tube amplifiers and similar.
- วิทยาศาสตร์และเทคโนโลยี
Many years ago I worked for a power supply company on radar transmitter power supplies. These supplies put out 24,000 volts and could supply many amps on demand and would kill you dead if you got across it..
One day while running a test sheet on one of these, I shut the supply down and prepared to remove the full load from the supply so I could record the output at minimum load. As I reached to move the alligator clip I first applied my shorting strap (#8 wire to earth ground - metal frame of the building, steel girder). The alligator clip at the end of the shorting strap was taped to a 12" phenolic rod so my hand was well away from the HV terminal. The result was a very load bang and a very bright flash, about 1/4" of that heavy alligator clip vaporized in that flash.
The power switch on the 30a variac had failed and the power was still applied so I put a direct short across that 24,000 volt power supply with a nice fat oil filled output cap. That caused a fault current of thousands of amps )24,000 volts / 0.02 ohms = ??). These supplied had previous melted a #10 wire inside the workbench wiremold strip, when I fixed that strip I found a 1/2" gap in the wire between a couple of outlets.
From then on I never relied on the switch, I ran the variac down to zero volts and double checked both the output voltage and the input voltage to make sure everything was off. I also kept the output of these supplies shorted to ground anytime i wasn't actively testing a unit.
This is an extreme example but it demonstrates how careful you have to be. When putting a resistor in a shorting lead make sure it can withstand the surrent flowing in it if it were hung across a working power supply supplying full output. Those sand resistors have pretty poor surge capability and can flash open if they are not rated for the surge.
Side note. When doing this in practice don't have both hands near the chassis or your heart can complete the circuit. One hand in the pocket.
A rectangular wooden block with a carve-out for the resistor and coated in epoxy and ergonomically shaped would have been much less costly and probably a lot safer than having the full voltage rod coming all the way to the handle. That’s worrisome.
Thank you! I just made one of these from stuff laying around my shop. Now I've got better safety for zero dollars. Winning!
Damn that grinder just absolutely murdered my eardrums
Thanks for the warning! I read that just before he turned it on 😄👍
😀
I realize this is an old video but it just appeared on my feed. When I do a job like this I use heat shrink tubing with adhesive in it. The adhesive prevents the tubing from sliding off over time, which does happen. Furthermore, the end of the tubing that protrudes past whatever is enclosed can be pinched closed. Finally, the same pinching method can be used when the tubing has shrunk the maximum amount but has not completely shrunk around whatever needs to be completely enclosed. Once again the end of the tubing can be pinched together to make an air tight seal. The seal also keeps moisture out which may help in high humidity when dealing with high voltages.
As an aside, I am just learning about tube amplification, just got my first tube amp, a single ended amp, and your channel has taught me a bunch about tubes. Since I was about 12 years old I have always been listening to solid state gear. Now it's back to tubes and I could not be happier.
Thanks,
Eric
Useful!
In PSUs, I sometimes see bleeder LEDs used as "idiot lights" to bleed/ indicate charge.
Adding one (or more) LED(s) to your probe, in series after the R, would be useful.
Nice vid on the instruction on the discharge divice, Chico-Detroit
Thank You So much ! for all of this information ! I recently purchased a capacitor discharger on Ebay and found it was good to 350v ! You may have saved me a shock ! . I am so much obliged for YOU Sharing your Expert Knowledge ! . You have helped me most incredibly ! I will build your design ! I am just getting into this as a 63 yr old ! YOUR GREAT !. Thanks so much. Kindest Regards .Nick.
Thanks, nice work. I was doing mine and I pretinned the part of the rod where I would solder the resistor. I made it a little quicker and cleaner looking.
Excellent Video. Thanks.
I use a resistor substitution box, having switchable resistances from 10 ohms all the way up to several megohms. Every electronics hobbyist should have one of these already anyway. You can start out the draining procedure with several hundred ohms selected on the switch and then rotate the switch down until you get to the lowest resistance. This makes for a safer, more thorough capacitor draining procedure then using just one fixed-value resistor* , and is much gentler on the capacitor. I did a upgrade the wattage of the internal resistors for everything below 100 ohms. It's an old Eico resistance box, by the way, extremely helpful for experimenting with circuit modifications, or dropping the voltages a little for comparison purposes when replacing incandescent lamps with LEDs, and so on.
* this is even more helpful for working on solid state equipment than for tube gear. Tube equipment won't care if you go to solder/unsolder something and there's 10 or 20 volts left sitting in a capacitor somewhere; but, if you try to solder/unsolder something in a solid-state amp that has 10 or 20 volts or more sitting on its capacitors, you are indeed very likely to blow up some other components and maybe damage even the circuit board if you unknowingly try to solder/unsolder something with that deceptive, seemingly "low" voltage on it. Also, know that typical tube amplifier capacitors are less than 100 microfarad and despite the high voltages, the amount of stored electricity is relatively modest and the capacitors are therefore easy to discharge; but a solid-state amplifier might have capacitors of 10, 000 microfarad that will hold a very large amount of current for quite a while in some amplifier designs, even though the voltages are much lower than you would see in a tube amp. A pair of undrained 6K to 10K mfd filter caps charged at merely 20 or 30 bolts will spark like a shorted out car battery, scare the crap out of you, beat up your soldering iron tip and vaporize copper foils, and probably short out some IC's or transistors, perhaps without any smoke or other visible indication of what has been damaged.
A lot of people might refer to what you described as a decade box.
Very nice. Thanks for sharing. Best, Don
Love the design. Thanks for sharing
Perfect job !!! only that !!! coooll and thanks for the share Mister ...
Neat tool. I've been using the low impedance mode on my multimeter to discharge caps for a while now, seems to work pretty well also
DON'T! 😵
The meter will/should have a fuse or fusible link in it, that can easily be blown by discharging a fat enough capacitor at a high enough voltage (especially if you accidentally leave the thing switched ON!);
Once that thing is blown, you have NO assurance that the capacitors are discharged.
@@RogerBarraud That's not how it works. The fuses in a multimeter are on the current ranges only and are linked across the terminals by a current shunt. And if you are using the current range to discharge anything, you could literally blow your meter apart and even injure yourself. The low impedance mode on the other hand is typically 5k - 20k ohms and is rated at the CAT rating of the meter, typically 600-1000V. Discharging anything rated above 1000V is something you would not do with a multimeter anyway.
Xraytonyb, Mr. Carlson and Mark. The Trifecta of tubes.
You forgot uncle doug
THIS IS GREAT!! THANK YOU!!
Very clearly explain and great job
Excellent video. I believe the old buzzard's called them Chicken Sticks.
Do more safety stuff. People either love it need it, if you know what I mean. My only idea is to maybe use two layers of heatshrink on the lower section. They always seem to get dinged up in my shop.
Excellent project. TY.
Very well done. Thanks
I'm about to pop open my old fender twin, this is just what I need to help me avoid an unpleasantly electrifying experience.
Amazing video
Excellent!
Nice Capacitor bleeder
Thank you! 😎👍
Great safety video! How it got any thumbs down is a wonder.
I built a few tube amps and always added a bleed resistor on all filter caps. Never needed to discharge anything on my builds
Excellent. Would have been good to incorporate a measuring device within the rod so you could see the stored current drain
I believe it's likely that we've all had a capacitor discharge tool that closely resembled a screwdriver. They can really scare the sh*t out of a unsuspecting beginner, or worse. Electronics really is not an intuitive subject as a whole to the uninitiated. It's unfortunate that most of us begin learning these valuable lessons without the advantage of having a ol' grey beard mentor. However, you learn really quickly the capabilities of capacitors, and that they aren't at all friendly.
Hey man go through the hardware section at lowes ir home depot. They have the 4-40 and 6 -32 machine nut and bolts, washers and lock washers. You like the black just make drill holes in a piece of scrap wood and load ten screws into the holes and hit with some black rustoleum. Any color you want. Save time and money, live better.
Thanks for making this video. Curious as to why you choose to use a brass rod. Was there a particular reason for using this material? Thanks
I did something stupid.
I built this tool and it works great.
I've used it many times while modding and testing my amp.
However the last time I used it I forgot to switch off the amp and only realised it about 5 seconds later because of the excessive sparking where the tool contacted my cap and the bleeder light not going out.
The amp appears to be fine but is there anything I should check out or weary of?
Thanks in advance.
I made something for the some use out of a old automotive test light .
What size resistor? I didn't get that part.
How large a cap can you use this on?
Only thing is that shrink wrap can easily be chipped or torn.
I would put the rod into a wooden dowel.
man! yeah! make it pretty! I'm gonna just use an big fat wire hanger and 3M green tape :^P --nice job tho.
I like it😊
My father had an old two cycle lawnmower, that had to be shorted, with the spark plug to the chassis. Apparently, my finger threw me about six feet, when I landed. LOL.
Nice device,i used a 1M resistor in line with heat shrink,think i'll get some nylon rod /tube and solder a resistor to a bannanna socket and a brass rod,fit it all inside the nylon tube or bored out rod,some epoxy and more heat shrink to isolate the brass rod up to the tip,and i can replace the plug cable,store the probe with no hanging cable yaddah yaddah yaddah.
1M Ohms is too high. It would take 1 hour to discharge. Use 470 Ohms. Unless you are playing with really low micro Farads.
With a 1M Ohms, your capacitors are not discharging.
Time_to_discharge = 5 * Farads * Resistor_ohms.
Great idea to make a simple useful tool. BTW, what is the power rating of the 120 ohm resistor; 10W?
Everyone else I’ve heard recommends a 100k or more resistor, not 100, rated about 3-5W. I think with 100 ohms it could discharge all at once, in one rush.
I have a 220 ohm resistor but it's 25 watts. Is that ok for 400- 600 Volts?
So this is good not only for guitar amps, but also other electronics such as vintage TVs and radios?
Yup. Any capacitor lower in voltage then the resistor and wire is rated for.
Outstanding video! Now question? You were to do a capacitor on a home ac unit and this might be a silly question but trying to make sure to drain the capacitor you attach the clip to the unit or the lip of the capacitor? I am using the screwdriver method and trying to touch nothing but that? Thanks in advance.
I would attach the clip further from the cap so my hands aren't in so close to the tip incase of accidental arcing. The clip can be attached to anything that is grounded such as the unit itself but that may be painted and blocking a good connection. I would think the 120v ground wire is exposed and a perfect place to grounds to bare copper and bolted to the chassis
The metal cans on a AC capacitor have no electrical connection to the capacitors inside of them. Make sure the Unit is FULLY DEPOWERED!! ( pull the outside disconnect and check both of your AC leads at the contactor for voltage across and to neutral / ground) If its a single cap, it will have 2 unmarked terminals. If its a 2 section, it will have a "C" for common, a "F" or "FAN" and a "H" or "HERM" (for "Hermetically sealed compressor motor") You wll drain the capacitors by going from "C" to "F" , and from "C" to "H" or "HERM"
What happens if that restor fails? Isn't HV just gonna jump through that heat shrinking tube?
Where I work with 250Kw SW transmitters-we use ground hooks.they are connected to the ground system of the station.Here the ground hook is your friend.Power supplies up to 30Kv-30A.the ground hooks WILL save your life.Use them anytime we go into a transmitter-also the primary breaker is opened.You have to open the breaker toget a key to gain access to the transmitters power vault.That contains the HV power supplies.The ground device you make is a good idea and precaution.
This could've been a 4 minute (at the longest) video.
I have a 1Kw Am vacuum tube broadcast transmitter. Dint remember off the top of my head how many voltsin the bug cPs. I'm thinking is either800, or 1,200. In the cBanit there was a probe wired to the ground of the mains ground o the end of a broomstick. Situation was I could have it,or if I didn't take it , it would get busted up and despised o,f who I thought would be A sin, so I have it. I thought maybe idtey to convert it to use on the 160M Ham band, but as yet haven't got my head around how to do that. Building suitable antenna and ground system at that ewavelength is also a but if a challenge, do even if I did s good conversion,, I dint have the avcwrage for a large enough antenna. 1kw AM RF INTO A SHORT ANTENa with iffy ground seems like are ipe for a lot of rfi complaints from too many too close neighbors, so that idea will have to wait until I land on a bigger plot with more distant neighbors. Those caps have big bkeader resistirs across them,, so discharging them hasn't really been an issue, buy that would be another thing if have to think that more fully when and if I put that beast back on the air.!
I would keep that ride is short as possible maybe only about 2 inches long just to get down onto your work
cap bleeder probe
Definitely a nice tool, but I'm a bigger fan of D-lab's method-- simply install a paralleled resistor in a dual banana plug connector, plug it into your meter, then plug your test leads into it. Set the meter to VDC, and you can discharge the capacitors while also verifying that they are, in fact, discharged!! (Just be sure to remove the banana plug device before using your meter for anything else!):
th-cam.com/video/2iqmDf0QIyM/w-d-xo.html
What watt?
I have somewhat of a video request. Could you explain what makes capacitors considered "audio grade," and which types of capacitors are recommend for the best performance in audio equipment? I typically use Nichicon caps per your recommendations, but are they all "audio grade," or are there specific types of Nichicons that are or aren't?
Mostly marketing strategy.
Audio grade capacitors are the 50 cent caps that cost $5.
"Audio Grade" caps are designed to have low internal noise so they will create less distortion passing an AC audio signal through an amplifier. They are usually in smaller values and voltages than power supply or blocking capacitors that are designed to manage high ripple current values for smoothing, or general purpose that may just hold or block DC in a circuit. If you go to Digikey or Mouser and search within the " Electrolytic Capacitor" for "Audio" capacitors, you can then select a few, and read the datasheet info on them and see what differences they may have from general purpose or other capacitors.
The service manual parts lists of my receivers NEVER say "use audiograde capacitors" as replacements. They state the microfarads and voltage. That tells you all you need to know about this scam.
Why not use something like a 10K ohm resistor to make sure it could handle the high voltage.
What’s thoughts on using a metal coat hanger in place of the brass rod, still using the heat sharing and resistor?
3-5 kv microwave cap people need to not mess with them if they don't know what they are doing.
Do you just touch the POSITIVE side of the capacitor, in order to drain it? A friend of mine who is a tech is suggesting to touch both capacitor legs at the same time "to be sure", but isn't that just shorting them, and is not only unnecessary, but actually not good for the cap? Thanks
Yes touching both without resistance in between is effectively a short. Maybe he's suggesting that to prevent accidental shorts if the leads are close (ex. radial capacitors). The safest way is probably clipping one side of the discharge tool to chassis ground and touching the positive side of the capacitor with the other end
@@monz7951 I think he is saying to do it the way that could potentially damage the cap! Which surprises me, because he is a very advanced tech. I'm going to chassis ground / touch positive. Thanks!
Hello and thanks for the tutorial, but i have one question. Other youtubers use in their tutorial a much higher value resistor like 20k and you use only a 120 one. Does that matter?
I know that a higher resistor will discharge the cap slower, but how about the safety aspect ? is it more dangerous to use a 100 ohm one compared to 20k one ?
Cheers !
I need To ask The Same Question Please .
It all depends on the rating of the capacitors you are discharging. Yes, 100 ohm CAN be bad if you're working with higher voltages. Personally, for most modern consumer electronics, I'd use around a 300 or 400 ohm resistor for a nice balance between time/safety. I'm thinking of making a tool like this that allows you to select from 3 or 4 different resistance levels. There are some web resources available to help you figure out what you should use. For example, DigiKey hosts a web page to calculate the appropriate resistor to use for a given capacitor: www.digikey.com/en/resources/conversion-calculators/conversion-calculator-capacitor-safety-discharge
That calculator tool is interesting. The caps discharge faster than I thought.
Yeah, I think the resistor I use is a 460. Works fine.
IREI red black gold and green
use chesil tips has better heat transfer.
I'd use a slim bottle and melt it over the whole thing. Happe safety people
How do you know when the capacitor has discharged
test with multimeter in DC volts
I've been bitten by a charged 300v capacitor before and I can tell you it stings!
@12:31 Next time try moving your stock of heat--shrink out of the way of your heat--gun blast. The red one starts to curl as it shrinks.
Oh a trick.... you can nick up the rod with a box cutter and leave micro barbs that will grab the heat shrink.
A dollar store ice pick works perfect. Blunt the point. The wood handle is an insulator.
High Blueglow Electronics. Can you make one for me that is 12 inches long ? I will pay you $10 dollars for it.
I suspect you electrician folk could make battery discharge amplifiers/enhancers piece of cake. Probably with some small pile on circuit intermediary. What gives
.... that's a long way of saying "grounded metal stick"
or you could use your multimeter it will drain too caps lol
120 ohm resistor way to small
OMG, Please stay away / out from all Fender model amps after the 70s!! They're extremely high in purchase price with extremely low quality electronic components !! They all fail in making amp techs money !! Wish there were videos on various amp manufacturers in demo / info the quality of build of there amps then move on to the sound of their amps !!!!
What a load of bull, as an EX: RTV bod from England, from 60'-2000's, Try working with 27 Kv with that crap. Stay off the drugs over there.
Not "bull", but he probably should have covered the fact that you need to pick resistors rated appropriately for the capacitors you're working with. Perhaps more constructive criticism on your part would have been to point that out, rather than saying "what a load of bull!" It may also have helped with your credibility to point out the reason WHY you felt it was insufficient instruction, rather than boast your years of experience and expect us to blindly trust your judgment. Honestly, I was under the mistaken impression people from England were more polite and thoughtful than Americans, but I guess your comment goes to show that people are just as rude everywhere.
please stay on your drugs over there.
stupid video I can't find the moment in which you're saying what VALUE resistor is needed
4:18 For anyone still looking.