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Comment by gumboza | Hacker News Reader

Definitely read the potential hazards section. Dangerous as hell these things.

Slap a "No user serviceable parts inside" sticker on it, and you have an unbeatable liability shield! /s

Yeah, they are dangerous, but their safety can be improved: add polarized cord (probably have to move the power switch to the hot side for this) and replace the chassis ground capacitor.

Table top FM radios and TVs also tend to be hot chassis.. (that mains transformer is just too expensive). Even today you can find capacitor dropper powered devices which are hot.

AA5s are nice in that you can almost always get them to work for cheap. I mean if you have an older radio with a bad mains transformer, it's probably not worth fixing.

Another advantage: they will work on 120V DC.

I don't think low end hot chassis radios were popular in Europe, they all seem to have a transformer. Maybe 220V is just too dangerous... (but you can certainly have a primary to secondary fault in a transformer..)

Polarised cord only works if your house sockets are wired correctly which is not necessarily the case and your earth bond might not be as good as you think it is. Always assume that the lowest competence is applied when it comes to safety evaluation.

At this point I wouldn’t run one of these things at all. If you drop dead you have no idea if some relative is going to plug it in and kill themselves with it. They were designed to a cost target when safety wasn’t a business concern. Steal the tubes and variable caps out and dispose of the rest. At best, stick it in a museum, preferably of dangerous things that should never be plugged in.

There’s plenty of tube kit out there you can buy which isn’t even remotely this dangerous.

Please do not willy-nilly dispose of beautiful pieces of interior design which likely won't ever be produced again with similar aesthetics. [1]

People constantly throwing away cultural heritage without any second thoughts is the reason why we barely have any left from only even more than 100 or 200 years ago - thousands of years of furniture, decoration, etc. are gone.

If you don't want them to be dangerous, make them safe.

If thats too complex for you, remove the cable and clearly label the backside with "DANGER! [...]" to explain that this shouldn't be used as is, and ideally put a letter inside which explains the technical details.

[1] Yes, I know there are things which are newly produced to "look" old. But they only do to people who aren't into that taste. If you are, all of the modern reproductions look like cheap, insufferable garbage.

I wonder why faux vintage stuff with modern electronics isn't more realistic and higher quality. It's not like high end woodworking isn't still a thing.

At the very least, if the alternative is full disposal, the old ones could be upgraded with modern electronics.

Okay but assuming there's no exposed metal parts, is one of these radios with a polarized cord really more dangerous than a regular old two pronged lamp with a polarized cord?

If you plug that lamp into an outlet with positive and neutral wired wrong you will have mains voltage on the light bulb threads and socket threads instead of ground, and that's gonna be pretty unsafe for anyone changing the bulb.

But lamps are so common, we don't even think about them as safety hazards.

240 was too high, and most of the non-110v sets use a transformer.

In reality, the case is meant to isolate the set, so the thing is only relevant when performing service work, and honestly, I just measure voltage between chassis and earth and make sure there is zero volts of potential.

That’s ok until you accidentally find you have an earth fault.

Well, in most cases I'm sitting on a chair isolated from earth, several feet in the air (wearing rubber soled shoes), so long as my test equipment shows 0v of potential to the chassis, its pretty safe. It could be that the earth bond has failed, but provided I have both pieces of gear sharing an earth, its all good.

Famous last words.

Leave that scope probe ground clipped on something and every earth is floating live on your bench.

Source: ex EE.

And at 110v, thats a risk I'm willing to take.

I wanna note, I worked as an FSE for a telecom, I've been 'bit' more than once by 130v, and by 160v B+ in shit, the sparks from crossed neutral are fine.

Anyone who is deeply concerned can buy an isolation transformer.

110v can fuck you up. Don’t take your own advice please. At least no one else should. Isolation transformer will only stop you getting killed one of three ways.

Worth backing my experience up as well. Ex EE covering RF and power in defence sector.

There is no room for arrogance or assumptions in dealing with safety.

How would you work on these things?

I wouldn’t. Simple.

Dangerous to poke around inside when plugged in, but quite safe unplugged (unlike say an old TV).

My dad used to repair TVs; I asked him what the easiest way to discharge a tube was and he said "grab the anode lead and the chassis" then after I gave him a look he said "well you didn't ask for the easiest safe way to discharge one"

DO NOT ASSUME a CRT MONITOR or 'old' TV IS SAFE to poke around when unplugged!!!!!!

https://www.instructables.com/How-to-take-apart-TV/

Read what I wrote again carefully, paying extra attention to the word "unlike"

"but quite safe unplugged"

a CRT monitor is typically (I would not gamble on it - again!) not safe when unplugged

Unlike means not like, so they were effectively saying it was safe to go inside radios but it is not safe to go into old televisions.

yes, you two are in agreement. it's the radio receiver that's safe when unplugged.

Not necessarily. The main filter caps can retain a high voltage depending on how it’s wired and if the designers installed a bleeder resistor and if the production guys didn’t remove it to save a few cents.

appologies - I just re-read the article (and the other comments). I see where you're coming from

I just saw the words "unplugged" and remembered the word vacuum tube - then massive emotions from my past came rushing through

Thanks, I did not know they were still dangerous when unplugged, but it kind of makes sense that they act as some kind of capacitor.

Why is an old tv unsafe?

The CRT acts like a capacitor, storing charge for quite considerable lengths of time. Consider that a B&W would typically run 10kV to 15kV, and color sets easily 25kV, and that should give you some idea of how much energy one of those things can hold. And with those kinds of voltages, you don't even need to make contact to find you've become a discharge path, that stuff will reach out and grab you across considerable air gaps.

oh, boy. the temptations of telling how to find out on your own are strong!

the capacitors in CRTs could store a charge for a long time. i've seen people that assumed the caps were discharged find out the hard way when they shorted the leads with a tool. the noise alone is enough to make one need clean shorts. the only good thing is that they discharge quickly, but they give you "both barrels" worth to borrow a phrase.

The CRT retains a high voltage charge even when the TV is unplugged.

CRTs hold a deadly charge for minutes to hours after being unplugged. CRTs can also emit x-rays if you bypass safety circuits. And touching a live flyback would be shaking hands with death. They were also manufactured before RoHS, so don't lick the PCBs or throw them in the ocean. Other than that, they're perfectly safe.

They're perfectly safe to work on, just measure voltage between chassis and earth and make sure there is zero volts of potential - or be fancy and use an isolation transformer.

You can still kill yourself with an isolation transformer fairly easily if you don’t know what you’re doing. See my other comments about earth assumptions.

Many consumer appliances are also still unisolated inside, it saves cost and you are unlikely to be touching anything inside if you don't know what you're doing (hence the usual "do not open" warnings on them.)

With tubes you were much more likely to touch stuff inside though, since they didn't last forever and people used to fix stuff more.

Yeah, do not attempt to use. High voltage inside. Better to buy any new low voltage piece of shit. Throw this all away. Be very afraid of this old stuff. Hmmm....your Tesla, runs on 3.7V LiIon...safe.

It is better to say that you should not go inside of an old television unless you know what you are doing, and don't assume that you know what you are doing unless you have guidance from someone who is experienced. Reading about or watching someone work inside of high voltage devices should not be considered sufficient since it is easy for either the author or reader to miss important details.

It is also worth noting that electrical safety depends upon far more than voltage. We think of 3.7 V battery operated devices as safe because our bodies are not very good conductors (when dry) and some types of batteries have an internal resistance that will limit the current draw. If I recall correctly, the internal resistance of LiIon batteries is sufficiently low that they are dangerous if not handled correctly (e.g. if you short them).

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