When I used to repair amps I used a 240 volt UK light bulb with 2 meter leads connected to it . You could see the bulb slowly get dimmer and then go out when discharged.
Thank you! This could save my beginner’s arse. I want to try an easy amp build, and I love looking inside my hand wired amps. Thank you for this video.
Exercise caution with voltage doubler power supplies, or those that output both positive and negative voltages using the same reference (some HV bench supplies, for example). They can have capacitors that are not grounded. Strapping your discharge resistor from B+ to ground won’t catch all of them. Discharge each capacitor individually.
Great tip. Learned that from my uncle who learned it from my grandfather. One thing to remember is use a resistor rated at the maximum voltage you will encounter. I once accidentally ordered the wrong series of metal film resistors from Dale. I wanted 750 volt rated resistors and ordered 250 volt resistors by accident. I would say they went poof the instant they had power applied but they didn't do anything but go open. No magic smoke, no snap crackle or pop, just went open.
Wait… this guy said to use a 22k 2 watt resistor. If a resistor max voltage is 1.5x the wattage, then a 2 watt resistor can handle a max of 3 volts. How can I tell the max voltage I’ll be dealing with within an amp? I’m planning to work on a fender blues Junior 15 watt amp.
@@chrissturley823 Not sure what math your using but it's not Ohm's law. Power (wattage) = voltage squared over resistance. That would give you the power dissipated in the resistor.
Terry, we need people who take an interest in our capacitors they are not made to last any more. Thanks, mate a good amateur always keeps his electronics working better and safe.73 de Dennis vk4oc.
Well, Snoz my Ramus! It's SUCH a no-brainer, I'm shocked (;-D) that no one's done that before! THANK YOU, Terry. Could save a life - or at least a nasty electrical discharge.
Thanks for the tip on the negatively-switched standby circuit. Never saw that before in an amp but the fact that if you don't know and you think you've discharged the caps is worth being aware of. Learned something new. Keep up the great work!
Back in the 70's I tested the length of time it took a charged capacitor to discharge in open air. It ranged from 30 minutes up to 3 weeks (!). The 3 weeks was on oil bath military capacitors from surplus equipment. Standard 'lytics took up to a week and a half, depending on their quality. Average on fixed caps was about 1-7 days, depending on capacity. Some of your viewers may be unaware that air blowing across the terminals of a capacitor can charge it. Many of the Mil Surp caps I bought back then had a shorting wire across the terminals. Your local electric company also has the shorting wires across the HV caps they use in your power system., until they are installed.
I looked at the schematic for my Vibrolux Reverb{AA270 circuit} and it doesn't look any thing like that, so I guess I'm good to go the old way of discharging caps. An old, long deceased amp tech once told me another way to discharge my caps: The day BEFORE I plan to work on my amp; turn off the power switch and unplug the amp from the outlet. Then flip on the standby switch. By the next day the caps will have discharged and the amp will be safe to service. Now, this was told to me back in the 1970s, and the guy worked on the circuits of those days. Nowadays, it could be a different story with all the different makes we have today. Then it was mostly Fender, Ampeg, Carvin, Marshall and Silvertone/Danelectro in my area.
In circuit, usually the caps will mostly discharge on their own as evidenced by your meter, as the tubes still draw a small amount of current as their filaments cool. That’s why the sound fades out vs abruptly cutting out. Greatest risk comes from when performing tests with the preamp and power amp tubes removed as now there is no current drawn after power is removed. In any event, it is still a good safety practice to measure the B+ rail before performing any service, and discharging the caps if necessary. I mitigate this in my designs by adding a high resistance (so it doesn’t load the power supply under normal operation) bleeder resistor across the caps so regardless of what state the amp is in, it discharges those caps when power is removed.
Excellent idea using that banana stacker. Maybe some heatshrink tubing over the resistor area of the stacker would be good. Looking at the Vibrolux schematic there is a ground connection at CP1? (can't read it) on the negative rail just after C33. Therefore with your banana stacker in place, the meter negative connected to the chassis and the positive connected to either TP33 or TP34, I believe the main filter capacitors would still discharge. As you rightly point out though , the voltage on all the other filter caps should be checked for discharge as well.
Jeff M Exactly so. The only thing the standby switch is shown as disconnecting here is the bottom of the bridge rectifier. The caps are still grounded. But a better reason to leave it on is so that the valves stay heated and so can still conduct away some HT.
If someone turns on the amp and doesn't wait long enough for the power tubes to heat up then flips the amp off. That will leave a very high potential for residual voltage in the caps, assuming amp does not have bleed resistors on filters. That's one advantage to having a tube rectifier in that it requires the same filament supply to be able to produce the DC voltage.
I meant to say flips the stand by switch on without waiting for tubes to heat up. Then turns amp off right away, all while tubes not having time to heat up and conduct. Not saying that will happen very often but it might when you are troubleshooting an amp on the work bench.
Ringo Starr As a matter of fact the whole standby switch thing is based on a fallacy. It is about preventing cathode stripping, but you need kilovolts for that to occur, i.e. transmitter valves. See here: debontamps.com/standby-switches/. They became a kind of fashion statement. I've even seen them in solid-state amplifiers, don't ask me why, and in fact I was once chastised by a band guy whose SS amp I had used during the solo act, for turning it completely off instead of just back to standby. He was convinced it was harmful. Couldn't be told otherwise. And I've seen tube amps whose solution to this non-problem was to put -750V on the grids for 40 seconds: cure somewhat worse than the disease.
Yup you are correct about cathode stripping occurring at high voltages. That SS must have been pretty old to have a standby switch, perhaps an old Vox amp? However the SS Vox amps from way back disconnected the speaker in standby mode which would at least get rid of pops when the amp woke up stupidly.
I know that a resistive discharge is better, removes the risk of damaging the cap and all but the dead short method is so much more fun ... 😉 Back when I was doing domestic field repairs, TVs mainly, I used to carry a ripple cap bypass tester made from a big cap with jump leads. If a customers little dog just wouldn't go away I used to charge the cap up from the power supply then short the crocs. Dog runs off in fright from the spark and the noise ... job done.
Brilliant! Thank you very much Terry! I love you channel and when a critical task can be completed with stuff just laying around. This freebie is right up there with the homemade Yamaha Subkick. Pitty the fool who buys something to do it. ;-)
Looking at the schematic, it seems like the main caps are still grounded even with the standby switch opened. The ground is at the right side of the picture. It's just the bridge rectifier and transformer that becomes ungrounded.
Question. When discharging tube amp caps, should the power cable be connected to the mains, while the amp is turned off? Otherwise, where will the charge dissipate via the chassis if the power cable is not connected to the mains ground? Or should the power cable be pulled out from the mains and chassis alone can absorb all that current?
Hey Terry, first off, thank you for these great videos! They are informative and fun. My question for you is: do you do this procedure with every amp you work on? I would assume so, but havent seen a video yet where youve done this. It appears like you go straight to touching everything so I was curious! Would you do this for every capacitor in the amp? Thank you.
I’ve been popped by one of these. Well, a Deluxe Reverb. I wouldn’t recommend it. Had to take a knee and check my vitals 😂. Safety practice is important, kids.
Enjoying your videos, Terry, but I think you are mistaken about the negative Standby on those Fenders. If you check the schematic closely, the caps are always connected to ground. They get lifted from the negative high voltage rectifiers, not from ground. So, they will still discharge by your method and most others. Keep up the good work!
Hi Jerry, So glad I found your youtube channel. Awesome job on your videos that are well done, easy to understand and the visuals are awesome. Thank you for what you do. I taught auto mechanics for 30+ years and really appreciate your professionalism. I do not have a banana plug setup on my Fluke27/FM meter. Any advice on how to build an adapter with the cap to do a power soak on the excess voltage and current? I'm working on a 67 Vibrolux, which is most likely similar to the Showman in your video, but then what do I know. My amp has a sizzle sound after striking a note that decays over a short time. She needs a tune up for sure. Doesn't have that warm Fender tone anymore. New tubes are on the way. I want to go over all the tube sockets to clean them and make sure they are not elongated. Do you have a video on tube socket maintenance? A few of the sockets look elongated. Well, I'll stop rambling here and continue getting educated with your fabulous work on amps. Thanks again, Dave
Thanks for all your quick tips keep up the good work keep the videos coming. Rectifier tube question and alternative use odd project. Would like to use a rectifier tube to build a low-voltage 5.3V 1.5A to 2A cell phone battery charger. I know it’s not practical, big bulky expensive if you had to buy the parts but if you have already had all the parts for free it should be possible?.
Is there any danger in poking around in an amp with the power trans primary still energised by the wall voltage? I've been shocked by picking up a chassis I thought was disconnected from the wall. Tired and late at night.
So when the standby switch is 'on' its actually an open circuit? Ie opposite of a light switch. As I (mis?) understand it the switch prevents the high voltage (from caps) from hitting a cold tube and creating an arc (hurting the cap and/or tube). So if you want to drain the caps grounding to the chassis, leaving standby ON creates a CLOSED circuit which allows the caps to drain. So why not just go from the positive to negative on each cap?
Thanks 😎 SIR..... Question... I have an old tube cabinet radio... I think philco... where in it would be model number Etc.... I have not disassembled the chasis yet.... it's a large chasis 24"by 10" loaded with large transformer and tubes alike hope to salvage parts but would like to aquire a schematics....
That's a great video! Now because you are a HAM what value resistor would you use on a 1kw linear amp for HF Radios? I've been using a 1k ohm 20 watt but think I've been doing it wrong also forgot to leave the stand-by switch in the "ON" WOW I'm glad I didn't get any shock ! Maybe those amps are a little bit different ?
When working on an amp with no standby switch, are there any rules to follow? A lot of the stuff I’ve been reading seems to be instructions for dealing with amps that have a standby switch. I’m assuming that I should just have the amp unplugged and go ahead and discharge the caps using this method. I bought the little banana piece and got a pack of resistors from Amazon. I’m going to set up my multimeter the same way they have it set up in this video. Is there anything else I should be aware of?
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.
What I don't understand is everybody says the same thing - don't put your hands inside the amp until you've discharged the caps. But you've got to put your hands in there to do that.
Just worked on an old Traynor YBA-1 and it has standby switch just like the Vibrolux. Thought about modding the switch to just break B+ directly instead of breaking ground in the bridge. The thought of extra long wires with B+ on a very quiet hum free amp kept me from performing the mod. I tend to check the caps right at the source so the standby wouldn't break the ground connection on the Traynor. In fact I bet on the Fender amp that caps are grounded even if the standby is on or off. Only difference would be if no groun reference on bridge then the D.C. Voltage will not flow into the circuit.
Yup just looked at the vibrolux schematic and cp38 is where the filters make contact with ground. The bridge is not directly grounded at the component connection point. So just don't connect negative lead of the meter at the center tap position on the bridge rectifier and expect that point to always be grounded.
Thank you for the upload good Sir! Can you please tell how many Omh resistor will be the right resistor for all voltage? Some say 120 and other 470omh 5w resistor! Which resistor do all jobs if I may say that?
Great videos!!! My 65 original blackface twin was capped and serviced last year...my question is do i need to discharge the chassis parts to spray out a few scratchy pots?? Thanks in advance Roger Rainville
A question please. At what point on the eyelet board are you discharging the caps from? Since I'm just a beginner when it comes to this stuff, I'd be more inclined to open the dog house and do each one individually, however, my guess is that you're doing it from the B+ rail past the standby switch from which point the internodal resistors and filter caps branch off. I've been zapped but just a few times over the years (luckily), but ever since I was knocked on my arse across the floor from my stereo speakers (electrostatics) I've had somewhat of an awakening...I'm just as cautious, if not more, with this stuff than I am working inside the live panel in my home which I'm used to. Thanks, JC.
Thanks! In that res with clips method, where do the extra electrons go when touching that metal case and is that case safe to touch after? (If can explain case ground, that would be appreciated)
Great tip thank you for posting this. I’ve found these stackable double Banana plugs but they all have an internal 18 gauge shorting bar. Don’t you want the path from + wire to - wire to pass through the resistor so it can restrict it before going to ground. Wouldn’t a shorting bar provide a direct path to ground?
I think that's okay because voltage in a parallel circuit is equal in all paths, so a resistor through one path will still have an effect on voltage in the direct path. Just a guess.
I just put an alligator clip and lead on each side of the caps, and just short/spark them out together, I've been doing it like that for years no worries.
In context of this video is "stand-by on" the position where you'd hear sound coming from the amp when normally playing amp or rather the position where power is cut from the power tubes and no sound? Thanks. I'm not sure everyone uses same terminology and it's obviously critical to this lesson.
@@soupalex Thanks. That's what I thought. But in my common use "put the amp on standby" means flip switch so no sound comes out and that also equates to "standby on". Maybe I've just had it wrong. But I don't really think there is a consensus on this.
it's not really helpful that a lot of other electrical appliances have a "standby" mode but only one power switch (i.e. they're only really "off" if you frob the wall switch or unplug them)
I did not know about the neg ativ standby switch. Thank you terry . i myself was using the a 1k 5 to10watt sandblock ceramic 5watt 1 to 10k .what is a gopd ohm value to use?
I bought this little box called a TKDMR Model: Td-CD01 Capacitor Discharger. It says suitable DC5 - 1000V that has these two little lights and says on it that discharge complete when light OFF. Is this suitable for capacitors in a modern amp? I have a Marshall DSL100HR head and can hardly find anything on it online other than I believe it as 2017 model amp. I'm wanting to discharge mine, so I can clean this damn yellow glue off the board they say could become conductive and seems to be touching certain components in the amp they say could later possibly short the map out and cause damage. The only amp repair guy around me wants to charge nearly $200.00 to do it. Its very little glue in a couple spots, and feel it's a rook for that much money. Or is this what amp tech charge now? or can I safely do this myself? I've always just played and had techs work on my stuff, mostly accept for biasing. Any advice?
Speaking for myself, it's possible I would turn the power back on and still have that resistor assembly plugged into the meter and connected to the hi V. Is there a resistor value that you would suggest that's high enough to use in that assembly and not damage anything should that happen?
Wouldn't a 450-volt shock be considered lethal? Scary stuff. A tube amp is not something you want to be poking around with unless you absolutely know what you are doing!
After you put a resistor into one of these plugs do you just clip off any extra length of the resistor wire that sticks out the other side? Should I cover the hole with anything?
is there a sure fire way to check voltage regardless of circuitry, what if completed the circuit between one end of the filter cap to the other with a resistor, or resistor and multimeter. does that eliminate all the charge regardless of where the standby switch is located?
When I used to repair amps I used a 240 volt UK light bulb with 2 meter leads connected to it . You could see the bulb slowly get dimmer and then go out when discharged.
Thank you! This could save my beginner’s arse. I want to try an easy amp build, and I love looking inside my hand wired amps. Thank you for this video.
Exercise caution with voltage doubler power supplies, or those that output both positive and negative voltages using the same reference (some HV bench supplies, for example). They can have capacitors that are not grounded. Strapping your discharge resistor from B+ to ground won’t catch all of them. Discharge each capacitor individually.
Great tip. Learned that from my uncle who learned it from my grandfather. One thing to remember is use a resistor rated at the maximum voltage you will encounter. I once accidentally ordered the wrong series of metal film resistors from Dale. I wanted 750 volt rated resistors and ordered 250 volt resistors by accident. I would say they went poof the instant they had power applied but they didn't do anything but go open. No magic smoke, no snap crackle or pop, just went open.
Wait… this guy said to use a 22k 2 watt resistor. If a resistor max voltage is 1.5x the wattage, then a 2 watt resistor can handle a max of 3 volts. How can I tell the max voltage I’ll be dealing with within an amp? I’m planning to work on a fender blues Junior 15 watt amp.
@@chrissturley823 Not sure what math your using but it's not Ohm's law. Power (wattage) = voltage squared over resistance. That would give you the power dissipated in the resistor.
The adapter mentioned is a Pomona 1330.
Best comment
Thanks, I was just about to look it up.
Terry, we need people who take an interest in our capacitors they are not made to last any more. Thanks, mate a good amateur always keeps his electronics working better and safe.73 de Dennis vk4oc.
Well, Snoz my Ramus! It's SUCH a no-brainer, I'm shocked (;-D) that no one's done that before! THANK YOU, Terry. Could save a life - or at least a nasty electrical discharge.
Thanks for the tip on the negatively-switched standby circuit. Never saw that before in an amp but the fact that if you don't know and you think you've discharged the caps is worth being aware of. Learned something new. Keep up the great work!
Just made this little tool. Haven't used it yet, but when I need it I'm prepared. Safety first.
Thank you for that great tip. I'm always a little on edge when it comes to capacitors.
I’ve been “on the edge” of a few of them.
Great tip Terry! Thought it was going to be the same method I always have seen and used, but I learned two valuable lessons here. Good job!
Very good Terry. You are correct in that standby switch is weirdly placed. Great idea with the banana jack.. as always. Thanks my friend. Ron
Exactly what I was looking for, thank you.
Back in the 70's I tested the length of time it took a charged capacitor to discharge in open air.
It ranged from 30 minutes up to 3 weeks (!). The 3 weeks was on oil bath military capacitors from surplus equipment. Standard 'lytics took up to a week and a half, depending on their quality. Average on fixed caps was about 1-7 days, depending on capacity.
Some of your viewers may be unaware that air blowing across the terminals of a capacitor can charge it. Many of the Mil Surp caps I bought back then had a shorting wire across the terminals. Your local electric company also has the shorting wires across the HV caps they use in your power system., until they are installed.
Great video, but you left no link for the banana adapter . . . . . . . D LAB is here for you.
Saint D lab thanks. I love your explanation for not technical speaking guys
I looked at the schematic for my Vibrolux Reverb{AA270 circuit} and it doesn't look any thing like that, so I guess I'm good to go the old way of discharging caps. An old, long deceased amp tech once told me another way to discharge my caps: The day BEFORE I plan to work on my amp; turn off the power switch and unplug the amp from the outlet. Then flip on the standby switch. By the next day the caps will have discharged and the amp will be safe to service. Now, this was told to me back in the 1970s, and the guy worked on the circuits of those days. Nowadays, it could be a different story with all the different makes we have today. Then it was mostly Fender, Ampeg, Carvin, Marshall and Silvertone/Danelectro in my area.
That's the method I've been using for years when working on tube amps and...I still have all my fingers ;)
Thank you Terry. This is a very nice tech tip which I will be using on my amp builds.
Such a nice and simple trick to solve this issue ! .............
Thank you for the safety tip Terry. Im very interested in learning about tube based electronics but the voltages are a concern for a neophyte like me.
Great video Terry! I always learn a lot by watching your videos.
Excellent video and tips, thank you. I'm building my first tube-amp kit and I've been looking for exactly this kind of info - the hows and whys.
In circuit, usually the caps will mostly discharge on their own as evidenced by your meter, as the tubes still draw a small amount of current as their filaments cool. That’s why the sound fades out vs abruptly cutting out. Greatest risk comes from when performing tests with the preamp and power amp tubes removed as now there is no current drawn after power is removed. In any event, it is still a good safety practice to measure the B+ rail before performing any service, and discharging the caps if necessary.
I mitigate this in my designs by adding a high resistance (so it doesn’t load the power supply under normal operation) bleeder resistor across the caps so regardless of what state the amp is in, it discharges those caps when power is removed.
Thanks so much D-Labs!!!
Great advice and great Channel!
Thank you !
Bob
That's very clever thanks for the excellent meter tip
Very informative, especially about the fender stand by switch. That's crazy. Great to know. Others might be like that.
Excellent idea using that banana stacker. Maybe some heatshrink tubing over the resistor area of the stacker would be good. Looking at the Vibrolux schematic there is a ground connection at CP1? (can't read it) on the negative rail just after C33. Therefore with your banana stacker in place, the meter negative connected to the chassis and the positive connected to either TP33 or TP34, I believe the main filter capacitors would still discharge. As you rightly point out though , the voltage on all the other filter caps should be checked for discharge as well.
Jeff M Exactly so. The only thing the standby switch is shown as disconnecting here is the bottom of the bridge rectifier. The caps are still grounded. But a better reason to leave it on is so that the valves stay heated and so can still conduct away some HT.
If someone turns on the amp and doesn't wait long enough for the power tubes to heat up then flips the amp off. That will leave a very high potential for residual voltage in the caps, assuming amp does not have bleed resistors on filters. That's one advantage to having a tube rectifier in that it requires the same filament supply to be able to produce the DC voltage.
I meant to say flips the stand by switch on without waiting for tubes to heat up. Then turns amp off right away, all while tubes not having time to heat up and conduct. Not saying that will happen very often but it might when you are troubleshooting an amp on the work bench.
Ringo Starr As a matter of fact the whole standby switch thing is based on a fallacy. It is about preventing cathode stripping, but you need kilovolts for that to occur, i.e. transmitter valves. See here: debontamps.com/standby-switches/. They became a kind of fashion statement. I've even seen them in solid-state amplifiers, don't ask me why, and in fact I was once chastised by a band guy whose SS amp I had used during the solo act, for turning it completely off instead of just back to standby. He was convinced it was harmful. Couldn't be told otherwise. And I've seen tube amps whose solution to this non-problem was to put -750V on the grids for 40 seconds: cure somewhat worse than the disease.
Yup you are correct about cathode stripping occurring at high voltages. That SS must have been pretty old to have a standby switch, perhaps an old Vox amp? However the SS Vox amps from way back disconnected the speaker in standby mode which would at least get rid of pops when the amp woke up stupidly.
Thanks for the tip Terry I was using the to ground method .
Love the banana clip trick. You’re the best, D-Lab. Aloha 🤙
I know that a resistive discharge is better, removes the risk of damaging the cap and all but the dead short method is so much more fun ... 😉
Back when I was doing domestic field repairs, TVs mainly, I used to carry a ripple cap bypass tester made from a big cap with jump leads.
If a customers little dog just wouldn't go away I used to charge the cap up from the power supply then short the crocs.
Dog runs off in fright from the spark and the noise ... job done.
Thank you Terry. Keep the videos coming my friend!
Very useful and instructive! THX!
Subscription earned! Thank you for posting this.
Brilliant! Thank you very much Terry! I love you channel and when a critical task can be completed with stuff just laying around. This freebie is right up there with the homemade Yamaha Subkick. Pitty the fool who buys something to do it. ;-)
Can you use 2 watt 20 k or 24 k or just 2watt 22 k...You the best I've learned so much from you...Jeff
Thank you, Terry. Very good advice.
Looking at the schematic, it seems like the main caps are still grounded even with the standby switch opened. The ground is at the right side of the picture. It's just the bridge rectifier and transformer that becomes ungrounded.
He doesn't know what he's talking about! I saw it too Russell!
Question. When discharging tube amp caps, should the power cable be connected to the mains, while the amp is turned off? Otherwise, where will the charge dissipate via the chassis if the power cable is not connected to the mains ground? Or should the power cable be pulled out from the mains and chassis alone can absorb all that current?
Notice the Hoppes No.9 on the work bench
Thanks, Terry!
Hello! Great video. Did you say you’ve been shocked by them???
Do I need to do this to replace my volume pot?
Hey Terry, first off, thank you for these great videos! They are informative and fun. My question for you is: do you do this procedure with every amp you work on? I would assume so, but havent seen a video yet where youve done this. It appears like you go straight to touching everything so I was curious! Would you do this for every capacitor in the amp? Thank you.
interesting and informative , thanks Terry !
I’ve been popped by one of these. Well, a Deluxe Reverb. I wouldn’t recommend it. Had to take a knee and check my vitals 😂. Safety practice is important, kids.
Damn, So it really must be a science project then. At least you survived.
Enjoying your videos, Terry, but I think you are mistaken about the negative Standby on those Fenders. If you check the schematic closely, the caps are always connected to ground. They get lifted from the negative high voltage rectifiers, not from ground. So, they will still discharge by your method and most others. Keep up the good work!
His explaination of how the Fender standby switch works,is not good work or thinking!!
Maybe he’s seen mods not wired correctly. Is flipping a switch that difficult?🤔
Thanks for a great tip I did not know that.
Thank you so much for your very helpful tips
I’m thinking of making it a habit to do the discharge dance with the standby switch in each direction
This is very clever thank you
thx terry every tip is useful to one and all :-)
Hi Jerry, So glad I found your youtube channel. Awesome job on your videos that are well done, easy to understand and the visuals are awesome. Thank you for what you do. I taught auto mechanics for 30+ years and really appreciate your professionalism. I do not have a banana plug setup on my Fluke27/FM meter. Any advice on how to build an adapter with the cap to do a power soak on the excess voltage and current? I'm working on a 67 Vibrolux, which is most likely similar to the Showman in your video, but then what do I know. My amp has a sizzle sound after striking a note that decays over a short time. She needs a tune up for sure. Doesn't have that warm Fender tone anymore. New tubes are on the way. I want to go over all the tube sockets to clean them and make sure they are not elongated. Do you have a video on tube socket maintenance? A few of the sockets look elongated. Well, I'll stop rambling here and continue getting educated with your fabulous work on amps.
Thanks again, Dave
Great video, as usual... thanks!
Hey Terry. Big fan of your channel. I couldn't help notice your load resistor plug. Do you have a tutorial on how to make one of those?
Hello, yes, I featured it on one of my past videos with a simple schematic, take a look
D-lab Electronics I definitely will. Thank you.
Great tips, man!
Thanks for all your quick tips keep up the good work keep the videos coming.
Rectifier tube question and alternative use odd project. Would like to use a rectifier tube to build a low-voltage 5.3V 1.5A to 2A cell phone battery charger. I know it’s not practical, big bulky expensive if you had to buy the parts but if you have already had all the parts for free it should be possible?.
Pretty Slick Terry Thanks !
Is there any danger in poking around in an amp with the power trans primary still energised by the wall voltage? I've been shocked by picking up a chassis I thought was disconnected from the wall. Tired and late at night.
So when the standby switch is 'on' its actually an open circuit? Ie opposite of a light switch. As I (mis?) understand it the switch prevents the high voltage (from caps) from hitting a cold tube and creating an arc (hurting the cap and/or tube). So if you want to drain the caps grounding to the chassis, leaving standby ON creates a CLOSED circuit which allows the caps to drain.
So why not just go from the positive to negative on each cap?
Very useful, thank you very much!
Thanks but a little confusing for me anyway. When you say standby switch “on” you mean NOT in the “standby” position correct?
Thanks 😎 SIR..... Question... I have an old tube cabinet radio... I think philco... where in it would be model number Etc.... I have not disassembled the chasis yet.... it's a large chasis 24"by 10" loaded with large transformer and tubes alike hope to salvage parts but would like to aquire a schematics....
Amazing ! thankyou.
Ah yes, the old Ass- kicker caps. I remember them well
But they did cure my depression
⚡🤯⚡🤯⚡🤯⚡
Hey Terry! Big fan. Great videos. Where can I get a D-lab shirt?
That's a great video! Now because you are a HAM what value resistor would you use on a 1kw linear amp for HF Radios? I've been using a 1k ohm 20 watt but think I've been doing it wrong also forgot to leave the stand-by switch in the "ON" WOW I'm glad I didn't get any shock ! Maybe those amps are a little bit different ?
When working on an amp with no standby switch, are there any rules to follow? A lot of the stuff I’ve been reading seems to be instructions for dealing with amps that have a standby switch. I’m assuming that I should just have the amp unplugged and go ahead and discharge the caps using this method. I bought the little banana piece and got a pack of resistors from Amazon. I’m going to set up my multimeter the same way they have it set up in this video. Is there anything else I should be aware of?
When you say to leave the standby switch in the on position, I take it that it's still disconnected from the wall socket/mains power source?
I’m needing to work on a newer vibrolux. Kinda scared to mess with it now!
What about amps without a Standby?
Thanks for your video btw, appreciate it 👍🏻
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.
What I don't understand is everybody says the same thing - don't put your hands inside the amp until you've discharged the caps. But you've got to put your hands in there to do that.
Wear insulated rubber gloves.
Hello Terry! What is the schematic that you use for this vibrolux? Is it AA964?
Just worked on an old Traynor YBA-1 and it has standby switch just like the Vibrolux. Thought about modding the switch to just break B+ directly instead of breaking ground in the bridge. The thought of extra long wires with B+ on a very quiet hum free amp kept me from performing the mod. I tend to check the caps right at the source so the standby wouldn't break the ground connection on the Traynor. In fact I bet on the Fender amp that caps are grounded even if the standby is on or off. Only difference would be if no groun reference on bridge then the D.C. Voltage will not flow into the circuit.
Yup just looked at the vibrolux schematic and cp38 is where the filters make contact with ground. The bridge is not directly grounded at the component connection point. So just don't connect negative lead of the meter at the center tap position on the bridge rectifier and expect that point to always be grounded.
Thank you for the tip !
Thank you for the upload good Sir! Can you please tell how many Omh resistor will be the right resistor for all voltage? Some say 120 and other 470omh 5w resistor! Which resistor do all jobs if I may say that?
cool vid and information, thanks 👍
Great videos!!!
My 65 original blackface twin was capped and serviced last year...my question is do i need to discharge the chassis parts to spray out a few scratchy pots??
Thanks in advance
Roger Rainville
Hey Terry, I want to get a big, lit magnifying glass like yours. Could you say where you got your one? Thanks! Lee
What if I am just changing a speaker, would i still need to drain? Amp has not been used in 3 months.
Hello...where can I buy that meter ad-on to discharge while reading voltage? Thanks
A question please. At what point on the eyelet board are you discharging the caps from? Since I'm just a beginner when it comes to this stuff, I'd be more inclined to open the dog house and do each one individually, however, my guess is that you're doing it from the B+ rail past the standby switch from which point the internodal resistors and filter caps branch off. I've been zapped but just a few times over the years (luckily), but ever since I was knocked on my arse across the floor from my stereo speakers (electrostatics) I've had somewhat of an awakening...I'm just as cautious, if not more, with this stuff than I am working inside the live panel in my home which I'm used to. Thanks, JC.
Thanks! In that res with clips method, where do the extra electrons go when touching that metal case and is that case safe to touch after? (If can explain case ground, that would be appreciated)
Great video. Thank you.
Great tip thank you for posting this. I’ve found these stackable double Banana plugs but they all have an internal 18 gauge shorting bar. Don’t you want the path from + wire to - wire to pass through the resistor so it can restrict it before going to ground. Wouldn’t a shorting bar provide a direct path to ground?
I think that's okay because voltage in a parallel circuit is equal in all paths, so a resistor through one path will still have an effect on voltage in the direct path. Just a guess.
@@AwesomesManvoltage will be equal but current will always flow trough the path of least resistance.
I just put an alligator clip and lead on each side of the caps, and just short/spark them out together, I've been doing it like that for years no worries.
In context of this video is "stand-by on" the position where you'd hear sound coming from the amp when normally playing amp or rather the position where power is cut from the power tubes and no sound? Thanks. I'm not sure everyone uses same terminology and it's obviously critical to this lesson.
in this case "standby on" means it's in the position you would need it at in order to hear anything out of the amp, yeah :)
@@soupalex Thanks. That's what I thought. But in my common use "put the amp on standby" means flip switch so no sound comes out and that also equates to "standby on". Maybe I've just had it wrong. But I don't really think there is a consensus on this.
@@BlackDotPatrick you're not wrong! i've definitely heard both uses wrt standby switches, i don't think there's a standard in common use at all
it's not really helpful that a lot of other electrical appliances have a "standby" mode but only one power switch (i.e. they're only really "off" if you frob the wall switch or unplug them)
@@soupalex Great video - and was wondering same thing on my Tweed Deluxe regards the standby switch "on" meaning. Cheers!
I did not know about the neg ativ standby switch. Thank you terry . i myself was using the a 1k 5 to10watt sandblock ceramic 5watt 1 to 10k .what is a gopd ohm value to use?
My amp doesn't have a standby switch. What's the procedure in this case? (besides buying another amp...)
I bought this little box called a TKDMR Model: Td-CD01 Capacitor Discharger. It says suitable DC5 - 1000V that has these two little lights and says on it that discharge complete when light OFF. Is this suitable for capacitors in a modern amp? I have a Marshall DSL100HR head and can hardly find anything on it online other than I believe it as 2017 model amp. I'm wanting to discharge mine, so I can clean this damn yellow glue off the board they say could become conductive and seems to be touching certain components in the amp they say could later possibly short the map out and cause damage. The only amp repair guy around me wants to charge nearly $200.00 to do it. Its very little glue in a couple spots, and feel it's a rook for that much money. Or is this what amp tech charge now? or can I safely do this myself? I've always just played and had techs work on my stuff, mostly accept for biasing. Any advice?
Speaking for myself, it's possible I would turn the power back on and still have that resistor assembly plugged into the meter and connected to the hi V. Is there a resistor value that you would suggest that's high enough to use in that assembly and not damage anything should that happen?
Wouldn't a 450-volt shock be considered lethal? Scary stuff. A tube amp is not something you want to be poking around with unless you absolutely know what you are doing!
Is the standby switch 'on' when there is sound or no sound?
Excellent!
After you put a resistor into one of these plugs do you just clip off any extra length of the resistor wire that sticks out the other side? Should I cover the hole with anything?
My old vox ac30 has no standby switch....whats the best way to discharge the caps?
is there a sure fire way to check voltage regardless of circuitry, what if completed the circuit between one end of the filter cap to the other with a resistor, or resistor and multimeter. does that eliminate all the charge regardless of where the standby switch is located?
What is that jack you plugged in to the speaker for the load?
Thank you!
Hi Terry ! Do I need to do the same thing with a solid state amp or not before attempting to work on it ? Many thanks John from England 😀
If you’re grounded and the powers off, with the resistor is it ok to touch other components with the wire your using to discharge the Caps?