View Full Version : Should I be shocked that I was shocked?


GeorgeHC
07-25-2016, 01:16 PM
I just picked up a nice late 50s/early 60s GE Ultravision TV this morning.

When I got it home, I started to clean it. I removed the knobs to let them soak in the sink for a while (they were quite grimy).

After a quick look inside and a vacuum of the chassis, I decided to power it up.

I plugged it in, and when I touched the metal on/off knob spindle I got one hell of a shock. The set powered up ok and seems to work well.

So is there something shorted out in the chassis? Or is this normal for one of these sets that has the "Chassis is connected to one side of power line" warnings? I find it hard to believe that the knob spindles wouldn't be isolated from the chassis.

MRX37
07-25-2016, 01:27 PM
Set that old, probably has a non polarized plug. You might have plugged it in backwards.

Otherwise... shorted capacitor, something else that shorted. Live wire touching chassis ground. Some other current leakage to ground. And yeah the knob spindles would very likely be grounded.

GeorgeHC
07-25-2016, 02:11 PM
So there is no way that I could have been shocked unless something is shorted out?

MRX37
07-25-2016, 02:52 PM
That's my guess. Or you plugged it in the wrong way making chassis ground hot, yet the set still works in spite of that.

Or, maybe it was just static electricity? You could try probing the knob spindle with a multimeter. See if there's current leakage to ground.

GeorgeHC
07-25-2016, 03:07 PM
No it was definitely not static... it was a sustained jolt that made my heart flutter.

How is it possible to plug in an ungrounded, non-polarized plug the "wrong" way?

Electronic M
07-25-2016, 03:11 PM
So there is no way that I could have been shocked unless something is shorted out?

Au contrare, it was likely that the chassis and knobs were live. That set looks to be more like a 1953-57 model (unless Canadian GE's were a few years behind), and it was not uncommon in the early to mid 50's for hot chassis sets to bolt the knob shafts directly to the chassis on hot-chassis sets. Many hot chassis sets directly connected the chassis to one side of the line (unless they were UL approved models which had a resistor/cap coupling line to line that could still give you a mean jolt). If the bare shafts don't protrude from the cabinet it is a dead giveaway that they are hot (but some hot ones don't warn you). GE was cheap, so if safety made them use more parts they would skip it if not mandated.

If a chassis is hot I always wear rubber shoes, and refrain from touching anything grounded.

MRX37
07-25-2016, 03:19 PM
Wow. Learn something new every day. Makes sense. So that's just the chassis operating "normally".

seriously that's scary that stuff was sold to the public.

maxhifi
07-25-2016, 04:04 PM
Au contrare, it was likely that the chassis and knobs were live. That set looks to be more like a 1953-57 model (unless Canadian GE's were a few years behind), and it was not uncommon in the early to mid 50's for hot chassis sets to bolt the knob shafts directly to the chassis on hot-chassis sets. Many hot chassis sets directly connected the chassis to one side of the line (unless they were UL approved models which had a resistor/cap coupling line to line that could still give you a mean jolt). If the bare shafts don't protrude from the cabinet it is a dead giveaway that they are hot (but some hot ones don't warn you). GE was cheap, so if safety made them use more parts they would skip it if not mandated.

If a chassis is hot I always wear rubber shoes, and refrain from touching anything grounded.

Yes above is 100% true never touch any internal metal
Parts oh hot chassis sets including chassis mounting screws and knob shafts. This applies to radios too.

GeorgeHC
07-25-2016, 04:08 PM
Wow thanks guys... amazing to me that they would intentionally wire sets like this.

Imagine how easy it would be for kids to pull the knobs off and get electrocuted!

I am always careful around the chassis itself but never considered the knob shafts as dangerous.

zeno
07-25-2016, 04:52 PM
A hot chassis is like touching one wire from an outlet.
One wont matter the other can kill you. Some sets have
a hot bridge ( like 80's GE's ) & it dont matter, its hot either way.
Use an isolation transformer & rubber soled feet.
Normally hot sets have plastic knobs with no chrome on the
shafts. Also insulated tuner & control shafts. You will also see a
lot of cardboard in them. One other thing is a fail of the
ISOLATED tuner balun. The antenna can go hot.
Best thing is to get a sencore PR57 or eq. It gives AC leakage test,
variac & isolation in one package. VERY useful on the bench
for many things.
Now you have had an AC shock so its time to get one from the HV
which is a quick SNAP. Then an RF shock thats like AC on steroids.

73 Zeno:smoke:

ppppenguin
07-26-2016, 02:31 AM
Live chassis sets (hot chassis in US English) were commonplace, both for radios and TVs. Saved the cost and weight of a double wound transformer. Because you guys across The Pond only use a puny 120V there was never quite the same need to keep humans away from the metalwork in the set. Here in the UK with 240V power it was a lot more important.

While it's best to connect the chassis of the set to mains neutral (cold) it's meant to be safe either way round. The antenna input is meant to be isolated with good quality capacitors in case the chassis is live (hot). Don't trust that these capacitors are still good.

Always use an RCD (GFI) in the power to sets like this. Then if the worst happens nobody gets hurt.

There are some sets where the incoming power is bridge rectified. In such sets the chassis is always at half mains (line) potential. A good trap for the unwary.

Don't assume the power switch in the set is OK. It's meant to be double pole but don't rely on either pole working. I learned this lesson at a very early age. I'd checked the chassis of a TV was safe. Turned off the switch and got a nasty belt from the chassis. The neutral (cold) side of the switch had failed int he closed position.

If you're using testgear such as a 'scope with a live chassis set then the correct way to do it is to power the set via a double wound isolating transformer.

Electronic M
07-26-2016, 09:28 AM
Here in the states unless there is an instant on circuit (which runs the heaters at half voltage when the set is off) most power switches were single pole...

Some transformer powered sets had a chassis to line resistor that could give you a tingle, and it was often wired so that when it would depended on how the un-polarized cord was connected and weather it was on or not.

dieseljeep
07-26-2016, 11:21 AM
Wow thanks guys... amazing to me that they would intentionally wire sets like this.

Imagine how easy it would be for kids to pull the knobs off and get electrocuted!

I am always careful around the chassis itself but never considered the knob shafts as dangerous.

The control pots and tuner shafts should be isolated by fiber washers or fishpaper sheets.
Look at the Zenith 7 & 8 tube FM-AM radios! Their chassis is as hot as the best of them, but see the effort put into making them shockproof. All the quality makes were that way.
The newer sets had captive knobs, nylon shafts, interlocking line cords, etc.
I'm still a great believer of GFCI receptacles. In old homes with no means of grounding, K&T wiring, Romex with no grounding wire, the GFCI receptacle will still give you the protection.

DavGoodlin
07-26-2016, 04:22 PM
Most series-heater (transformer-less) radios had the chassis connected to one side of the line and very few had polarized plugs, even after all the series-heater TVs had them. Often, the AC line went via the power switch right to the chassis, so adding a polarized cord without rewiring this condition was of no benefit.

Some of the higher-quality radios had the chassis connected to line or "B-" via a capacitor, .05 mf or so. The metal chassis was more of a signal ground.

The first TV repairman I worked for said the most dangerous voltage in a TV was the 120 volts AC feeding it. The 400 volts B+, boost, focus and HV would hurt but you seemed to recoil AWAY from those as discharges, causing cuts or worse from the reaction.

maxhifi
07-27-2016, 09:50 AM
Here in the states unless there is an instant on circuit (which runs the heaters at half voltage when the set is off) most power switches were single pole...

Some transformer powered sets had a chassis to line resistor that could give you a tingle, and it was often wired so that when it would depended on how the un-polarized cord was connected and weather it was on or not.

There's also chassis to line capacitors which can go leaky. I got a shock from an old EICO oscilloscope, which has a power transformer, on account of leaky line to chassis capacitors.

Electronic M
07-27-2016, 11:29 AM
There's also chassis to line capacitors which can go leaky. I got a shock from an old EICO oscilloscope, which has a power transformer, on account of leaky line to chassis capacitors.

I've seen those, but I usually change them even if good so I never have to deal with or think of their shock hazard.

ppppenguin
07-28-2016, 02:23 AM
Chassis to line caps must be replaced with Class Y types. Likewise any cap whose failure would give a shock hazard. @Electronic M is very sensible when he replaces them regardless.

This page is written from a largely US/Canadian perspective but it's just as relevant in Europe where the higher mains voltage is more dangerous if something goes wrong: http://www.justradios.com/safetytips.html