High voltage jolt Shocking surprise from Danelectro vintage tube guitar amp beware of this hazard

[@garydrouin143]

Hey terry I just finished repair on the same amplifier Silvertone1334 and got shocked when I pulled the RCA plug. The Silvertone has noval approcach on baising the 6L6s, from pin 8 on the 6l6s in series with two 12AX7 heaters filaments to ground, provides 20 volts of bais no cathode resistor or bias supply. The cold filaments in series measure about 30 ohms, applied ohms law the hot filaments are about 300 ohms right in the ball bark. Your viewers may have never seen this scheme.

[@robinsattahip2376]

Glad you were not hurt, a shock once in a while is a healthy reminder. Here in Thailand (and in most of the world) I have to deal with 240 vac line voltage.

[@williambock1821]

It’s definitely a reminder. Healthy,I don’t know.

[@giulioluzzardi7632]

Thank's D-lab, take no chances when working with Electrickery! Seriously important reminder especially in these times of DIY repairs and modifications. A good tech will always put safety 1st, a great tech will teach others the ways to avoid harming others. Champion job Man!

[@petercornell2002]

Damn-electro..... Glad you're OK Terry.

[@theoloutlaw]

Wow! You can never underestimate the intensity of Electricity, no matter how much experience one has. Thanks Terry, for always addressing and reminding people of it's hazard with precautions.

[@rb032682]

That old guitar amp shock. LOL! In 1966, my very first guitar performance in front of people was cut short before it started when I touched my mic with my mouth while I had my guitar in my hand. I was shocked so badly, one side of my face was numb for about a half an hour and the audience had a great laugh. The mic was in a different amp and one of the amp chassis was at a high voltage, (not ground). These kinds of shocks were quite common for local guitar and bass players in the 1960s until around the mid-70s. If you're gigging, always carry a cheap AC wiring checker. Many clubs have very poor wiring which violates multiple electrical codes.

[@iandeare1]

Advice I've often advocated, and especially in relationship to badly earthed equipment, and mains hum! Unfortunately, so many times I've been attacked about citing grounding issues as you describe, by people, unlike myself, who don't even declare any electrical qualifications, I've literally been told it doesn't happen, and as a consequence I've given up on mentioning it... Although, I do still reccomend a simple mains tester plug, make sure your fuses are right, and don't overload sockets (the UK does have slightly different domestic wiring rules, and of course domestic 250V 13A supply)

[@cloudconnect]

Not just Danelectro named, but all Danelectro-MADE amplifiers, so Silvertone, Supro, Airline, National, Gretsch, and a few others I may be forgetting, had this, but only for the two-chassis (top and bottom) units. The shield on it carries high voltage ground back to the main chassis. If that connection every gets loose, or sounds dirty, never ever start fiddling with it while the amp is on. Why the ground isn't in the bunch of wires that goes in the multi connection tube-like socket on these amps is beyond me. Anyways, thanks for turning a negative into a positive, Terry. I've learned the hard way too.

[@cloudconnect]

People who are still confused: There is a multi-connection plug from the pre-amp chassis to the main chassis that Terry didn't mention. You can see all of the multi-coloured wires in the first part of the video, just at the top of the speaker. One of those wires carries the high voltage, but weirdly, the ground was left out of there and they used the RCA shield instead.

[@rossthompson1635]

Thanks - I was going to ask if there was a secondary fault causing the potential or if this is a design problem - seems to be the latter. Wow!

[@Greenballed]

Now I get it. I couldn’t understand how that power was getting routed that way until you explained that.

[@dughuff8825]

Seems a bizarre idea to ground the chassis in this way - I'd have expected the ground connection to be part of the umbilical; which is I guess what Terry expected as well.

[@johnmellor3048]

THANK YOU, Terry! Glad you're OK. This video could save some lives out here in the world of electronic tinkerers.

[@mikemoyercell]

Glad you are here to talk about it!! Yeah you don't want that kinda voltage going through your heart!

[@rightlurker4674]

Whooo boy, I've been tinkering with a Gibson GA-79 that has split preamp/power amp sections connected by an umbilical cord. I never would have thought of this. So thanks, Terry, and glad you're alright.

[@zbaby82]

Wow Terry. I'm glad you're okay.

[@tubeztoonz]

Very glad you’re OK, Terry!

[@jamiboothe]

Once I grabbed the tip of a lawnmower spark plug, while the lawn mower was running. It had no rubber grommet over it. I did that only once. Thanks for your safety heads up, Sir Terry The Brave, and still living.

[@paulomeyer3900]

Happy that you still here...

[@Fetishom]

See what carefull practices save life ? Using only right hand that is. I’m glad you’re ok. I remember years ago, plugging a tuner into an amp with rca. I got a 120 volt jolt. The tuner had the case at one side of the line!

[@mikesmuseum]

This is why the 'one hand rule' can save your life. It's a good thing you didn't fling your hand into those glass tubes and get cut up. Stay safe, Terry.

[@christopher_fyfe]

Exact same scenario happened to me when working on a Silvertone amp of same design... Very scary setup... Glad you are OK.

[@jemshawful]

This looks like a "newer version" of the 4x 6v6 pioneer amp which had similar rca connection to main chassis But didn't have a pre amp tube on the upper chassis so no high voltage , looks like they just made a few changes without thinking it through (or caring). It did however carry the grid bias for the preamp tube ( which heaters were supplied by and mostly created the bias for the power tubes :) expect the unexpected ). That being said sounds pretty good. Glad you survived and also didn't throw the chassis across the room (unintentionally or not)

[@scottlee1211]

Glad you are ok Terry! That’s why I send my stuff out to people like you that are qualified to perform work on those units as well as older radios! Only thing I claim to know about electricity is….it will hurt me!!!

[@eugenepohjola258]

Howdy. Credits to You. Takes a man to admit one's carelessness. And better still. Making an educational video about it. I had a somewhat similar experience. I was commissioning my KT88 PA and got a jolt when plugging in the signal jack. I use free floating chassis techniques. I use a separate minus wire as a minus bus. So there was voltage between the signal plug casing and the chassis. I had wound the output transformers myself. Somehow one primary winding turn had collapsed through the bobbin. Probably a crack in the bobbin. Inserting the laminates one laminate had scraped off the turn lacquer. The short propagated from the core to the chassis. I was lucky too only using one hand plugging in. And yes. It felt like my whole hand had been hit by a hammer. In High Regards.

[@kookoogearkook]

Glad your okay!

[@jcmcclain57]

Good to practice that rule of only one hand in the chassis… Very glad you are OK. Thank you for sharing this “I learned about electricity” moment with your viewers with a test setup verifying the ungrounded potential between the chassis.

[@MrSteveCasper]

Glad you're alright Terry! Thanks for sharing this story I'll file it in the old noggin and be extra careful next time I'm messing around.

[@itsonlyme9938]

Glad your ok terry that was a close call. I have a Heathkit SB200 I always unplug it before doing any work on it and wait for the HV, 2500 to discharge.

[@rciancia]

I love the resistor teeth.. LOL The best... HAHAH - Glad you are ok Terry, that pretty messed up 400+Vdc.... great safety tip brother !!!!! thank you

[@jeffbrooks7246]

Really happy you are not hurt and thank you for that very important tip my man.

[@edwardhannigan6324]

OMG Terry..Shows you, no matter how safe you think you are, sometimes bad surprises hit you..! Sure glad you're OK man...Very informative.. Take care please..Ed..UK..😢

[@NINEWALKING]

Glad to see you are alright. Close call. I guess left hand in pocket when amp is powered rule saves life’s. Man in such situation one would easily want to stabilize the thing catching parts using both hands. More you doo with amplifiers more safe you feel and that might lead to do stuff in improvised scenarios. Like let me just quickly test it. It is going to hold for that time. I am guilty of that as well. Costed me a tube or two. Best way is to always take the time and make safe setup where nothing can move. Last time I have worked on the combo amplifier that has no jack for the speaker. Even worse, the external speaker jack was on the back panel. So when you just want to take the chassis out you get everything tethered to it. You get be short cable to the panel and second short cable to the cabinet. To just check the bias you need to desolder something. Take time and do it. That’s my 2 cents.

[@johnbravo7542]

Thanks for the video,hope you are Ok Terry,see you on the next upload

[@richardcron2395]

Ouch! I'm happy you lived to fight another day.

[@ivetoldyouonce]

Glad it was enough for a teaching tool and not any worse.

[@bobboyle7629]

Wow. By posting this, you might just have saved someone's life, Terry. Good to Know!

[@Xpyburnt_ndz]

OUCH!!! Glad you're OK Terry! I got hit once with 480V out in the field as an electrician 35 yrs ago and it locked me up!!! Yes, I chewed the other guy out, up one side and down the other, who unlocked the lockout on the panel!!! 🤬🤬🤬🤬🤬

[@bulldogavenue]

Holy Cats! glad you are okay. Will file this one away for future repairs. Stay well and thanks for sharing!

[@wp4electronics998]

Glad you’re fine.

[@bobblum5973]

I'd like to see a schematic for that guitar amp, just so I could understand why they did it that way. It sounds like they just decided to use the RCA cord to tie the chassis "grounds" together, but that's just asking for trouble. Glad you weren't hurt much, Terry! Back in the mid-70s my tech school taught the "one-hand rule" when working with high voltage equipment. Over the years I've been fortunate to only get bitten rarely. One time at a military electronics manufacturer, we had 400 Hz 120 VAC to power the aircraft devices. Getting hit with that felt _very_ different from 60 Hz!

[@tpaairman]

I found one on EL84 world for a model 89 which from what I can find is very close. it took me a minute to figure it out, but that there is no direct ground connection between the two panels except the audio connection. What's even more bizarre is there is the filament of the 12AX7 on the preamp side, which is in series with a filament on the power amp side. They run between the cahodes of the power output tubes and the ground side of the audio jack in the preamp side. There is a plug between the two sides that includes the B+, as well as the connection between these two tube filaments. So if you disconnect the audio line between the two, you still have a ground connection via the two series filaments, but your hand would probably be a path of least resistance.

[@bobblum5973]

@@tpaairman "A ground connection" using the filaments isn't necessarily the same as a true ground. What were they thinking when they designed this? 🙄🤦‍♂️

[@tpaairman]

@@bobblum5973 As I'm looking at it further, it's actually not another ground-ish connection. it's how they tied the cathodes of the output tubes to ground, which makes it an even stranger design.

[@bobblum5973]

@tpaairman It reminds me of a piece of military test equipment I worked on at the manufacturer. All the indicator lamps were 28 volt miniature flange base. That made sense since it was used to test aircraft on the flight line or in the field. But I noticed a 28 volt lamp connected to the 115/120 VAC 400 Hz main power feed. Checking the schematic showed a _capacitor_ being used to drop the voltage down to 28, matching its impedance at line frequency to do the job. Why do it that way? Then I realized that ALL the lamps were the same, so they only needed to stock one type out in the field. So like in the case of this amp, they may have had some reason behind why they designed it that way, we just may never find out what it was. 🤔🙂 Side note: That 28-volt lamp running off 115 volts was a military-style push to test lampholder. I dug into the circuit while testing, discovered the lamp holder was mis-wired, so pressing it to test put the 28-volt lamp _directly_ across the 115 volts. POP goes the lamp! 😁

[@daveanderson5680]

I guess that DanElectro was a Damn Electro

[@geemac7267]

Thank God you're okay. If it can happen to you, it can happen to any of us.

[@vadenk4433]

Holy smokes that’s scary. Glad you’re alright Terry

[@DeadKoby]

I've got my share of zaps as a technician too. They all serve as a learning experience.

[@tschupbach]

Seems strange they would depend on the input jack for a ground. I'd probably look at the main plug connecting the two units and see if there isn't a failed ground there. That would also explain the noise.

[@iandeare1]

Had something similar, forty odd years ago, from a 150 W PA valve Amp. The isolating cage/cover was off, I reached into adjust something, and inadvertantly touched chassis, and a HT valve top cap at the same time: I was literally thrown, unconscious, 6' across my bedroom, came too slumped against the wall, literally wondering what the hell had happened!

[@Brian-yt8fu]

Glad to see ok. Had your other hand been touching the other chassis you might be in heaven now.

[@cheycasters]

You the man Terry no doubt!!!!! Thanks man🎸🎸

[@brentnearhood8874]

Thanks! D-Lab

[@DemonKingOFFICIAL]

I got shocked once when working on my Peavey Valveking. Just barely though. Was modding the power board to allow for a 50w mode and my finger grazed something hot by mistake. Was quite surprising lol!

[@loumonte658]

Wow that was a close call. Stay safe.

[@jonathanbobohunt6507]

I got 454 volts in my hand once ( voltage went through my thumb through my hand to ground) when a tube cooler melted into a wire on the output transformer so I know where you are coming from. glad you are okay.

[@shckltnebay]

tube cooler?

[@MrMeik1970]

Oha ,Thanks Terry 👀

[@poisedforduty]

Thanks for the public service announcement

[@hestheMaster]

"Remember kids electricity can kill you." - Reddy Kilowatt

[@jenniferwhitewolf3784]

Close call there... an important lesson in just how potentially dangerous high voltage equipment can be, sometimes in unexpected ways.

[@Spookieham]

Nasty glad you are ok.

[@livewire4495]

Sounds like your voice went up an Octave Terry. I have had a few bites in my day. A three phase 440vac back fed crane rail circuit got me one time. I thought I was dead and so did my Partner. Always check for potential. That near miss taught me a lesson that saved my ass more than once during my 49 year career as an industrial Electrician. Can't see It. Can't smell it. Can't Hear it.⚡⚡BANG!

[@ne2i]

Crazy design. Quite unsafe to have separated grounds.

[@NINEWALKING]

I think the actual issue is that they are using that main chassis ground true that cable only. So once disconnected preamp chassis doesn’t have ground anymore. Still big design flaw and potentially deadly one too.

[@pearsedunne9938]

Yikes, I know how it feels. It happened to me many times working on old vintage British tube amps back in the 70’s. Absolute death trap when you’re between ground and stray B+. Extreme caution should be taken seriously. Good warning on KZbin, Terry……👍🇮🇪

[@jerryking2418]

great advice.

[@Route66Wanderer]

Imagine if you had a load resistor on your 10 meg high impedance multimeter or better yet, a good old 20,000 Ohm’s per volt Simpson 260. You would not have seen that high of a voltage. It’s important to understand the limitations of the test equipment. This phenomenon is actually well known with AC as a Ghost Voltage.

[@jeremywinnett6352]

Widowmaker, in typical Dan-O style.

[@AndreaAustoni]

Be careful, Terry!

[@danrussell9357]

Glad the video was 4 minutes; otherwise, we would have to call it a short : )

[@d-labelectronics]

Yep, it was a bit short, without the actual shock footage

[@danrussell9357]

@@d-labelectronics Glad you can share about the experience so calmly. Thanks for the content!

[@sw6188]

I'd like to see a schematic for that amp too. Even with an audio ground between the two chassis removed, you still shouldn't have HT on the pre-amp chassis! Either there's a really bad design fault or someone has done a bodge job and connected something incorrectly (or both) or a component has let go (think death cap) and livened the chassis enough to give you a belt but not enough when the grounding cable is connected that it blows the fuse.

[@tpaairman]

I found one on EL84 world for a model 89 which from what I can find is very close. it took me a minute to figure it out, but that there is no direct ground connection between the two panels except the audio connection. What's even more bizarre is there is the filament of the 12AX7 on the preamp side, which is in series with a filament on the power amp side. They run between the cahodes of the power output tubes and the ground side of the audio jack in the preamp side. There is a plug between the two sides that includes the B+, as well as the connection between these two tube filaments. So if you disconnect the audio line between the two, you still have a ground connection via the two series filaments, but your hand would probably be a path of least resistance.

[@sw6188]

@@tpaairman That sounds like a nightmare. I never understand why manufacturers choose to do things the hard (and potentially dangerous) way when they can just as easy choose to do it the right (and safe) way.

[@tpaairman]

@@sw6188 Typically it's doing it the cheapest way possible. Got to save that 7 cents per unit by not having to run an extra wire.

[@sw6188]

@@tpaairman Yes. many pieces of equipment were built to a price. I have worked on quite a few items from the past which were built with as few components as possible. They started with a design, then looked at every single component and tried to work out a way to make the unit still work without that part.

[@josephcote6120]

Is there a schematic for this? I'd like to see how they could have set it up that badly.

[@dhpbear2]

Assuming everything is connected up normally, wouldn't strapping the chassis together create a ground-loop?

[@cloudconnect]

No, because the whole point is to get rid of that ground in the RCA cable, altogether, by disconnecting at the source side. The best way would probably be to put the ground in the same plug as the high voltage supply. Then you could never have one attached without the other.

[@pauldow1648]

How could this have been prevented ? Isolation transformer ? Circuit schmatic analysis ? Other ? Or maybe not at all !

[@scottbc31h22]

Danelectro schematics can be hard to find. But the problem arises from poor design. Both the audio ground and the DC voltage ground are shared by the RCA cable. Not a good idea. I don;'t think the design would pass Underwriters Laboratories listing. If the RCA cable is pulled, there is no path for DC voltage to return to the negative terminal of the power supply (ground). This is not a situation one would expect to find. I would look to see if there is/was a ground connection that came loose. If not, Terry;s fix is correct Some amps that have two chassis have a multi pin power supply connector on the cable between the two chassis, It would be OK to run the ground wire through this connector.

[@mpirron1]

Secure your chassis when removed for in-circuit testing

[@bobblum5973]

Terry, here's a thought: how much current is passing through the RCA cable's shield? It would be interesting to rig up something, such as a current meter or a voltmeter across a low-ohm resistor in series with the shield, and _carefully_ measure it. I've always avoided or minimized current in the shield for audio signals to reduce noise from current loops; this sounds like it was designed to encourage it instead.

[@russellhltn1396]

Sounds like it's the entire B+ power is going though that.

[@bobblum5973]

@Russell Hltn I could see it going that high because that voltage potential is being applied to the circuitry in the (currently ungrounded) secondary chassis, and with no return path (no ground) it just tends to follow any path to ground available (Terry's hand, in this case!). It's not the high voltage itself that's dangerous in and of itself. It's like building up a static charge on yourself, you're fine until you touch something and discharge at a high rate.

[@cloudconnect]

@@bobblum5973 I think you are right. Normally, it is not that much voltage going up to that single 12ax7, but when you disconnect it, it will read much higher on the meter. It's still probably just under 200v under normal operating, though, and whatever current a 12ax7 manages to draw.

[@paulomeyer3900]

Hi, Terry. I don't know this amplifier or its schematic, but I assume that the pre and power units have their power coming from a single source. Isn't it a case of unifying your grounding, without using the RCA connector? Just curiosity...

[@sundogaudio851]

thats exactly what he was suggesting for a ground runner.

[@luthiervandros]

I got hit by a Musicman. Agh. No more late night work.

[@clarkturner7484]

Wow. What a dumb design. The HV line should be shielded or a ground runner at minimum. Reminds me of the death-O-matic Heathkit chiipiwa amp. This thing has a plastic meter with full 3000 volts on the meter. If amp was on and you rested your hand on amp near that meter, You where dead. They also had a MALE pin plug on the power supply! So if ya unplugged it, the pins had full voltage like 500 screen right on the plug!!!. Glad you are ok man.

[@johnmorgan2043]

How can I get ahold of you to inquire about purchasing a small tube build of yours

[@d-labelectronics]

See my contact info on d-labelectronics.com

[@neccron9956]

What is causing it?

[@zulumax1]

I don't see how that kind of high potential could leak on to the sub chassis, unless you have a shorted tube, tube socket, or leaky bypass capacitor. (DC) edit: removed comment on leaking AC current which was not the case here.

[@cloudconnect]

It's not leaking. Its all contained within a wire. Unfortunately that wire is the shield for the RCA cable, and that's it.

[@zulumax1]

@@cloudconnect So that is the return path for the B- current? Probably from the cathodes?

[@zulumax1]

@@cloudconnect Had to think about it for a few and realized if you open the circuit to the cathode current which is usually going through a resistor to chassis, the chassis voltage will float up to the same potential as the plates. Riding the short bus I guess.

[@tpaairman]

@@cloudconnect I found a schematic for a model 89 on EL34 world. Long story short, other than the audio cable between the two, there are two tube filaments in series. One on the pre amp side, one on the power amp side. There is also a plug that has the B+ line, and a connection between these two filaments. The filament series connects between the cathodes of the power output tubes and the ground side of the audio jack. So, that is the only other (kinda sorta) ground connection.

[@1974UTuber]

What would be the reason for having the 2 chassis with different ground potentials? Would that just be a design error? Or would they do it for a reason?

[@cloudconnect]

Best to look at a schematic, and it will show it somewhat. There is that RCA plug and a multi-connection plug Terry didn't mention. Search Silvertone 1433.

[@mackfisher4487]

Little or no Shock Hazard: Purchase cheap Chinese battery-operated amplifiers, not those dangerous Gibson motivators. Kidding Aside, the longer one work with this stuff the more you become complacent how we all been poked a few times but the more accidents one has more potential for electrocution. How many times do we forget to turn off the power, or when troubleshooting a hot chassis get distracted. (Thanks Terry for reminding me)

[@cloudconnect]

Or work when tired or frustrated. All_the_bloody_time.

[@rciancia]

Electricity is like a caged animal. Always looking for a way to get out

[@buzzedalldrink9131]

if i understand this correctly the B+ is going through the rca cable to the other chassis?? if thats the case I am surprised this amp has not killed many over the years

[@d-labelectronics]

Nope, the shield of the RCA cable connects the 2 chassis grounds

[@buzzedalldrink9131]

@@d-labelectronics Thank you and I am very glad you are OK

[@Hammerjockeyrepair]

if you picked your boogers while working your other hand will always be busy!

[@spooky3120]

God was looking over you. It could have been MUCH worse.

[@doctorcircuit5338]

I've been fried a few times over the years 🤔 and it shows 🎉

[@flintdavis2]

Why don't you tech guys wear gloves?