Thank you... Working on a rf amplifier... Just got a nasty burn... I got lucky... I paid the minimum price for a life threatening lesson... Thank God... Play safe and have fun...
You're welcome. Glad I could help. I've been zaped twice. Both times I was measuring and adjusting voltages. Always keep one hand in your pocket and the ground clipped on. Probing with both hands could ruin your day! Cheers.
Cool upload Mike, I made a 10w 100ohm version years ago, think I got the idea from Uncle Doug but seems I am wayyy under the mark so I am going to make an upgraded version today...as my father used to say..."Boy with pliers, mess with wires, blue flashes.......grey ashes"
Glad it inspired you. I’ve made a few and I seem to always grab the steel rod one that I made. Just seems to fit in the hand nicely and can get into tight spaces.
I usually just use an alligator clip lead connected to ground and the tube side of a plate resistor. If you hav an amp with a storage cap on the hot side of a standby switch make sure you close the switch.
Thanks for commenting. Yes, that is another way to do it. You can also add a high value, high voltage rating “bleeder” resistor into the circuit at the PSU section is also a good idea.
I've seen quite a few videos on making these. In one video someone demonstrated their probe on a cap charged to 450 volts.. There was a meter connected. They touched the probe and the voltage dropped to near nothing. They removed the probe and the voltage had climbed back up a certain amount. Connecting a resistor creates an RC circuit with an associated time constant to discharge. This is why for my probe I put an insulated alligator clip on the end and leave it connected for several seconds allowing me to do something else. I also used a fairly low value resistor to cut that time down. I will admit though a 'touch' probe is better than nothing.
Yes, you are correct. It does climb back up a bit but only a few volts. I typically touch for 5-10 seconds. But yes, attaching clips to let it drain for an extended period of time is also a good idea.
Thanks for the video. So putting two resistors in series will indeed double the resistance? Example 500ohm plus 500ohm would equal 1000ohm? Does this have the same affect on the wattage rating as well? Have my parts on hand, so I will make a couple of these so I safely do some minor work on my amps.
Yes, you are correct and that will work just fine. Probably want to go with at least 5 watts each. Most tube amp drop voltages pretty quick... ie charge curve... that last remaining volts are a lot lower and take additional time to zero out.
Hi Mike, thanks for making this video. On wattage of the resistor, you used a 25 watt for yours. How important is the wattage of the resistor? I have a 10 watt 1000 ohm resistor in my spare bin I was looking to use. I'm looking to discharge my AC capacitor. Thanks
Thanks for commenting. 10watt will be fine if you use it small to medium tube amps. When they are off it’s just a instantaneous current spike then it drops rapidly. (As per the time constant). At 500v a 1000ohm resistor could see 0.5amp for a split second then rapidly decrease. What you can do it put two larger ones in parallel or two smaller ones in series for added protection. Cheers.
Thanks for the great video. I have some hifi amps with virtually all popropyelene non polar caps - even the PSU caps, which are Solen polypropylenes. If you have non polar caps instead of polar, can you discharge the cap in the same way (one end of the wire to chassis and other to one end of the cap?, - If so, I assume it doesn’t matter which end you touch on the cap?) Or can you not use the one wire end to ground technique for non polar caps? I’ve seen other videos where people just use a resistor ends going tk each end of the Individual cap end, - instead connecting one end to the chassis. That looks more inconvenient though. Any advice would be appreciated.
Hello, thanks for commenting. Even though Solen Caps are not Polarized, they still need to be drained (especially if they are in the PSU section) Since the negative side is already at ground potential, you still need to drain the B+ rail side (just like in the video) then test with a Multi-meter. Some caps in a circuit are bypassed with a resistor and will drain quickly but you should try to do every cap and test before you work on an amp. Cheers.
@@MikeFreda Hi Mike. Thanks a lot for the reply. Much appreciated. The problem is, as these caps in my monoblock 300B amps are non polar, I’m uncertain which side of them is the B+ side. (I didn’t build them myself). It’s not obvious like it would be with an electrolytic polar cap (where you can easily identify the positive end of each cap) Would a reasonable strategy be to connect one end of the meter to the chassis ground then touch (one after another) each end of each cap with the other probe of the volt meter (with resistor installed). I assume nothing will happen when you touch the end of each cap which is at ground, and you’ll get draining of the cap when you touch the other B+ end. My amps have wooden cases so that’s obviously not appropriate to fix one probe to for ground. The Top plate however is metal. I assume that would be ok as ground? Or maybe another technique might be to touch each of the probes ends on each end of each individual capacitor (instead of connecting one probe to chassis ground) . I’ve seen people do this before, sometimes just using a resistor between the ends briefly. It obviously takes much longer though than the other method. There is probably also a higher chance of putting both hands inside the amp at once!, which worries me!
I see, well, not knowing how your amp is wired/made I can’t really comment on the process. All I can say is use a tool like mine and touch the leads on both sides of the caps. One side should be grounded and then a multimeter to confirm the amp is fully discharged.
OK, all clear except one thing. At the 3;00 mark, you say “we’ll solder the end on”, but what exactly is that black cord? Wire spec? Don’t you have to first strip the end off from that black cord?
Thanks for commenting. When editing, I thought that was self explanatory. Yes, strip the end of the wire, solder and cover it with heat shrink. Don't let it ground out on the rod portion of the tool. Standard hookup wire is okay. 22-18 ga is fine. There isn't a lot of current here so wire size is not that important just as long as it rated to ~600volts. Cheers
Hi, you can but I would recommend using a screwdriver that is voltage rated. Milwaukee, Klein and Wera make them. I would also use voltage rated heat shrink as well to cover up any loose leads. Cheers
Yes, they can be. It really depends on the PSU design, voltage rating of the amp how large the caps are. A large value capacitor (i.e. 1000mfd) at 100V can still pack a punch. Always a good idea to drain the test with a multimeter. Cheers
Yes... sort of. This value can range from 500R to 5k. It basically adjust the discharge Time Constant a little. Lower value increases the Time Constant and could create a spark. Realistically, higher voltage caps that we typically see in tube amps rarely go above 400ufd so anything in that range will work just fine. You will see that in the first 1/2 sec the voltage will be high (~300VDC) and drop to 10v.. to make it got to zero may require ~5 to 10 more seconds. Also, if you have many good quality large value caps, you may see the voltage start to rise again (0-3volts) due to its original charge. That's why bleeder resistors are a good idea. Always confirm with a DMM. Cheers
Yes. Solid state amps typically run at a much lower voltage than tube amps but they do have power supply capacitors to filter the AC ripple out of the DC. They are typically a higher value in capacitance but a lower voltage rating so there still is a risk. Some have draining resistors but it’s still a good idea to measure and/or drain. Cheers.
It depends what the size of the capacitor is. If it’s just a standard run start one then yes. If it’s a larger home rated for very high voltage you would need to calculate the RC time constant of that just to make sure it is safe. But the general idea would be the same.
Mike I am new to this and really want to get started building some small amps and doing maintaince on my amps. This info is so appreciated. What amp kits would you recommend ?
Thanks for commenting. People have said this before to me. I thought it was pretty self explanatory just hooking up some resistor in series with the rear wire lead and clip. I can draw you a picture or detailed photo if you like. Cheers.
Surely you jest!? To be honest, when I first started I just used a multi-meter and measure and drain the PSU caps. (20+ years ago). I did eventually get shocked when it was a little too complacent. I always drain the caps now when I work on an amp. Doesn’t take much to ruin your day! Cheers.
You skipped something buddy. You inserted a red insulator in between the two black shrink tube insulators. I assume you snuck that in after soldering the resister to the probe. And why are you insulating a capacitor from the probe? Shorting out? That's the purpose of the capacitor.
Thanks for commenting. Sorry, I didn't really miss a step. I just tried to condense the video down a bit to get to the point. You basically want to bond one end of the large resistor to the front of the steel probe and cover everything else with heat shrink. (I just used red since that's what I had that fit nicely.) The back end of the resistor has the wire soldered onto it. That wire goes to the insulated clip that is grounded on the amp. You are just making a temp resistor node to ground. There is no capacitor. I did up a drawing and linked it the video description. I hope it helps? Cheers.
This is the best video on how to discharge Caps. I'm going to be building these today.
Glad I could help! Be safe out there. Cheers.
Thank you...
Working on a rf amplifier...
Just got a nasty burn...
I got lucky...
I paid the minimum price for a life threatening lesson... Thank God...
Play safe and have fun...
You're welcome. Glad I could help. I've been zaped twice. Both times I was measuring and adjusting voltages. Always keep one hand in your pocket and the ground clipped on. Probing with both hands could ruin your day! Cheers.
Instructive, entertaining, promoting best practice and safety.
What's not to like!
excellent work.
Much appreciated! Cheers
Cool upload Mike, I made a 10w 100ohm version years ago, think I got the idea from Uncle Doug but seems I am wayyy under the mark so I am going to make an upgraded version today...as my father used to say..."Boy with pliers, mess with wires, blue flashes.......grey ashes"
Glad it inspired you. I’ve made a few and I seem to always grab the steel rod one that I made. Just seems to fit in the hand nicely and can get into tight spaces.
I usually just use an alligator clip lead connected to ground and the tube side of a plate resistor. If you hav an amp with a storage cap on the hot side of a standby switch make sure you close the switch.
Thanks for commenting. Yes, that is another way to do it. You can also add a high value, high voltage rating “bleeder” resistor into the circuit at the PSU section is also a good idea.
Great idea and I think useful for hvac tech also rather than shorting with a screwdriver like i have seen in many hvac fix videos. Thanks
You’re welcome! Cheers.
I've seen quite a few videos on making these. In one video someone demonstrated their probe on a cap charged to 450 volts.. There was a meter connected. They touched the probe and the voltage dropped to near nothing. They removed the probe and the voltage had climbed back up a certain amount. Connecting a resistor creates an RC circuit with an associated time constant to discharge. This is why for my probe I put an insulated alligator clip on the end and leave it connected for several seconds allowing me to do something else. I also used a fairly low value resistor to cut that time down. I will admit though a 'touch' probe is better than nothing.
Yes, you are correct. It does climb back up a bit but only a few volts. I typically touch for 5-10 seconds. But yes, attaching clips to let it drain for an extended period of time is also a good idea.
awesome video, well done man
Thanks for commenting. I’m glad you liked the video and found it helpful. Cheers.
Thanks for the video.
So putting two resistors in series will indeed double the resistance?
Example 500ohm plus 500ohm would equal 1000ohm? Does this have the same affect on the wattage rating as well?
Have my parts on hand, so I will make a couple of these so I safely do some minor work on my amps.
Yes, you are correct and that will work just fine. Probably want to go with at least 5 watts each.
Most tube amp drop voltages pretty quick... ie charge curve... that last remaining volts are a lot lower and take additional time to zero out.
Resistors do add in series. A 100 ohm fed into a 200 ohm fed into a 50 ohm would give you an equivalent resistance of 100+200+50 (350) ohms
Hi Mike, thanks for making this video. On wattage of the resistor, you used a 25 watt for yours. How important is the wattage of the resistor? I have a 10 watt 1000 ohm resistor in my spare bin I was looking to use. I'm looking to discharge my AC capacitor. Thanks
Thanks for commenting. 10watt will be fine if you use it small to medium tube amps. When they are off it’s just a instantaneous current spike then it drops rapidly. (As per the time constant). At 500v a 1000ohm resistor could see 0.5amp for a split second then rapidly decrease. What you can do it put two larger ones in parallel or two smaller ones in series for added protection. Cheers.
Great vídeo Mike! Thanks for share!
You’re welcome!
Thanks for the great video.
I have some hifi amps with virtually all popropyelene non polar caps - even the PSU caps, which are Solen polypropylenes.
If you have non polar caps instead of polar, can you discharge the cap in the same way (one end of the wire to chassis and other to one end of the cap?, - If so, I assume it doesn’t matter which end you touch on the cap?)
Or can you not use the one wire end to ground technique for non polar caps?
I’ve seen other videos where people just use a resistor ends going tk each end of the Individual cap end, - instead connecting one end to the chassis.
That looks more inconvenient though.
Any advice would be appreciated.
Hello, thanks for commenting. Even though Solen Caps are not Polarized, they still need to be drained (especially if they are in the PSU section) Since the negative side is already at ground potential, you still need to drain the B+ rail side (just like in the video) then test with a Multi-meter. Some caps in a circuit are bypassed with a resistor and will drain quickly but you should try to do every cap and test before you work on an amp. Cheers.
@@MikeFreda Hi Mike. Thanks a lot for the reply. Much appreciated.
The problem is, as these caps in my monoblock 300B amps are non polar, I’m uncertain which side of them is the B+ side. (I didn’t build them myself). It’s not obvious like it would be with an electrolytic polar cap (where you can easily identify the positive end of each cap)
Would a reasonable strategy be to connect one end of the meter to the chassis ground then touch (one after another) each end of each cap with the other probe of the volt meter (with resistor installed). I assume nothing will happen when you touch the end of each cap which is at ground, and you’ll get draining of the cap when you touch the other B+ end.
My amps have wooden cases so that’s obviously not appropriate to fix one probe to for ground. The Top plate however is metal. I assume that would be ok as ground?
Or maybe another technique might be to touch each of the probes ends on each end of each individual capacitor (instead of connecting one probe to chassis ground) . I’ve seen people do this before, sometimes just using a resistor between the ends briefly. It obviously takes much longer though than the other method. There is probably also a higher chance of putting both hands inside the amp at once!, which worries me!
I see, well, not knowing how your amp is wired/made I can’t really comment on the process. All I can say is use a tool like mine and touch the leads on both sides of the caps. One side should be grounded and then a multimeter to confirm the amp is fully discharged.
OK, all clear except one thing. At the 3;00 mark, you say “we’ll solder the end on”, but what exactly is that black cord? Wire spec? Don’t you have to first strip the end off from that black cord?
Thanks for commenting. When editing, I thought that was self explanatory. Yes, strip the end of the wire, solder and cover it with heat shrink. Don't let it ground out on the rod portion of the tool. Standard hookup wire is okay. 22-18 ga is fine. There isn't a lot of current here so wire size is not that important just as long as it rated to ~600volts. Cheers
Hi mike can i make resistor weld on metal scewdriver im not sure.thanks
Hi, you can but I would recommend using a screwdriver that is voltage rated. Milwaukee, Klein and Wera make them. I would also use voltage rated heat shrink as well to cover up any loose leads. Cheers
Thanks for this video.
You're welcome. Its a great tool to have. Cheers.
Good job
Are the capacitors on solid state amps just as dangerous?
Yes, they can be. It really depends on the PSU design, voltage rating of the amp how large the caps are. A large value capacitor (i.e. 1000mfd) at 100V can still pack a punch. Always a good idea to drain the test with a multimeter. Cheers
820 ohm does depend on the Cap value, doesnt it?
Yes... sort of. This value can range from 500R to 5k. It basically adjust the discharge Time Constant a little. Lower value increases the Time Constant and could create a spark. Realistically, higher voltage caps that we typically see in tube amps rarely go above 400ufd so anything in that range will work just fine. You will see that in the first 1/2 sec the voltage will be high (~300VDC) and drop to 10v.. to make it got to zero may require ~5 to 10 more seconds. Also, if you have many good quality large value caps, you may see the voltage start to rise again (0-3volts) due to its original charge. That's why bleeder resistors are a good idea. Always confirm with a DMM. Cheers
Can some respond this? Are Solid state amps safe to operate into them or I need to do the same thing
Yes. Solid state amps typically run at a much lower voltage than tube amps but they do have power supply capacitors to filter the AC ripple out of the DC. They are typically a higher value in capacitance but a lower voltage rating so there still is a risk. Some have draining resistors but it’s still a good idea to measure and/or drain. Cheers.
Can you use it to safely discharge a capacitor in a central air conditioner?
It depends what the size of the capacitor is. If it’s just a standard run start one then yes. If it’s a larger home rated for very high voltage you would need to calculate the RC time constant of that just to make sure it is safe. But the general idea would be the same.
@@MikeFreda Thank you for your prompt reply. My A/C capacitor is 45 + 5.0 mfd, 370-440 VAC, 50-60Hz, protected 10,000AFC
Do u do commission?
Hello, unfortunately, on this tool or tube amps I don’t, sorry.
Mike I am new to this and really want to get started building some small amps and doing maintaince on my amps. This info is so appreciated. What amp kits would you recommend ?
Would like a video on real time, not sped up so the viewer can see what is being done, I personally would rather have a normal speed video
Thanks for commenting. People have said this before to me. I thought it was pretty self explanatory just hooking up some resistor in series with the rear wire lead and clip. I can draw you a picture or detailed photo if you like. Cheers.
That was a great answer. @@MikeFreda
Use 250volt lamp and watch it dim.
What about a 25w bulb?
nah i live life on the wild side
Surely you jest!? To be honest, when I first started I just used a multi-meter and measure and drain the PSU caps. (20+ years ago). I did eventually get shocked when it was a little too complacent. I always drain the caps now when I work on an amp. Doesn’t take much to ruin your day! Cheers.
You skipped something buddy. You inserted a red insulator in between the two black shrink tube insulators. I assume you snuck that in after soldering the resister to the probe. And why are you insulating a capacitor from the probe? Shorting out? That's the purpose of the capacitor.
Thanks for commenting. Sorry, I didn't really miss a step. I just tried to condense the video down a bit to get to the point. You basically want to bond one end of the large resistor to the front of the steel probe and cover everything else with heat shrink. (I just used red since that's what I had that fit nicely.) The back end of the resistor has the wire soldered onto it. That wire goes to the insulated clip that is grounded on the amp. You are just making a temp resistor node to ground. There is no capacitor. I did up a drawing and linked it the video description. I hope it helps? Cheers.