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.

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.

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.

The adapter mentioned is a Pomona 1330.

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.

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.

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.

Just made this little tool. Haven't used it yet, but when I need it I'm prepared. Safety first.

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!

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.

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.

Saint D lab thanks. I love your explanation for not technical speaking guys

Exactly what I was looking for, thank you.

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

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 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!

Thank you for that great tip. I'm always a little on edge when it comes to capacitors.

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.

Thank you Terry. This is a very nice tech tip which I will be using on my amp builds.

Great video, but you left no link for the banana adapter . . . . . . . D LAB is here for you.

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.

Such a nice and simple trick to solve this issue ! .............

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.

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.

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.

Thanks so much D-Labs!!! Great advice and great Channel! Thank you ! Bob

Thanks for the tip Terry I was using the to ground method .

Very useful and instructive! THX!

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.

Thanks, Terry!

Thank you Terry. Keep the videos coming my friend!

Subscription earned! Thank you for posting this.

Thank you, Terry. Very good advice.

Very useful, thank you very much!

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. ;-)

This is very clever thank you

Love the banana clip trick. You’re the best, D-Lab. Aloha 🤙

interesting and informative , thanks Terry !

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

Thank you so much for your very helpful tips

Great video, as usual... thanks!

Amazing ! thankyou.

Great tips, man!

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

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.

Pretty Slick Terry Thanks !

Thanks for a great tip I did not know that.

thx terry every tip is useful to one and all :-)

I’m thinking of making it a habit to do the discharge dance with the standby switch in each direction

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!

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.

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.

Thank you for the tip !

Great video. Thank you.

cool vid and information, thanks 👍

Thank you!

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.

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?.

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

Good info. thanks

Excellent!

Ah yes, the old Ass- kicker caps. I remember them well But they did cure my depression ⚡🤯⚡🤯⚡🤯⚡

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?

I’m needing to work on a newer vibrolux. Kinda scared to mess with it now!

Many thanks

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.

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.

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....

Thank you!!! 😊

good tip

Thanks

Thanks but a little confusing for me anyway. When you say standby switch “on” you mean NOT in the “standby” position correct?

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?

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?

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?

How about hifi tube amps without standby switch?

What if I am just changing a speaker, would i still need to drain? Amp has not been used in 3 months.

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...where can I buy that meter ad-on to discharge while reading voltage? Thanks

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 ?

Hey Terry! Big fan. Great videos. Where can I get a D-lab shirt?

The moment you were talking about getting shocked... ive never seen your face so serious in any of your videos... never been zapped my self... musta sucked bad for you to get so serious(face) about it.

My amp doesn't have a standby switch. What's the procedure in this case? (besides buying another amp...)

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

Hello Terry! What is the schematic that you use for this vibrolux? Is it AA964?

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?

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?

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.

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?

What about amps without a Standby? Thanks for your video btw, appreciate it 👍🏻

My old vox ac30 has no standby switch....whats the best way to discharge the caps?

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?

What if your amp has no standby

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?

When you say leave the standby switch "on," do you mean in the "standby" position or the "on" position?