Where live chassies banned on Australia

[Telecolor 3007]

Is true that live chassies where banned in Australia (on live chassies you don't have a transformer, so you may get 110 or 220 V on the chassie => risk of electrocution)

[kx250rider]

They should have banned them here... SO many people died from those little metal radios from the late 30s. Some even had metal knobs. I have a friend who lost his frat brother that way while he was at USC. Came home and found the guy in the bath tub dead, with a 5-tube metal radio on a table next to the tub. Metal knobs, guy's arm slumped out of the tub below the radio. (Happened in the mid-1940s). Those are often called "Suicide radios" buy collectors. I've been knocked across the room by F-connector receptacles on various TVs, in cases where the polarized plug was defeated, or where the house was wired backwards.

With all the lawsuits everywhere in today's society, I can't believe they still have live-chassis items on the market today in 2009.

Charles

[AndrewM]

The live chassis was never banned here in Australia. There have been transformerless sets (radios) available since the 1930's or even earlier. These were mostly imported radios or local sets made for AC/DC operation.

Monochrome TV's with a live chassis have been imported for sale here since 1956 and some local manufacturers made sets that were live chassis, though they were not a common practice.

When colour TV was introduced in 1975 the majority of sets were based on European designs or directly imported so many had a live chassis.

The use of transformerless sets was discouraged for a while (during the late 1950's or early 1960's I think) because the electricity companies did not like the effects some of these sets had on the power grid. This was mainly due to the uneven power usage of sets using half wave rectification.

[Telecolor 3007]

Is that true that some folks liked Soviet tv's because they had transformer?

[nasadowsk]

I'm amazed the live chassis set wasn't banned in the US. It was a truly stupid design idea. Most live chassis stuff worked like crap, anyway.

As for a live chassis TV? these days, I'm amazed - switching power supplies are so cheap to build it's amazing.

[old_tv_nut]

I once encountered a European set that had some sort of bridge rectifier arrangement that guaranteed the chassis was hot no matter which way the plug was inserted (wish I could recall the details). I had it on the bench at Zenith to do some comparison of video output circuits, and got fireworks when I first connected the scope probe ground, so reversed things and got fireworks again!

We also once had a workbench moved that mistakenly got wired backwards -oops! All communicatins with the electrician were through the building manager, so I don't know if he got a reprimand. Once bitten, twice shy, so ever after, I checked any new wiring myself before using a bench.

[peverett]

I have some of the early 1940s radios. Mine are bakelite, but the screws on the bottom connect directly to the chassis which is live. Also, if you loose a knob, you are in trouble. A very dangerous design.

By the mid 1940(just after WWII, the power was coupled to the chassis via a 240k resistor or so and a capacitor. This is somewhat safer unless the capacitor shorts.

I also have 1953 model Hoffman TVs with live chassis. The Tubes are on a filament transformer, but the DC supply grounded on the chassis. Hoffman used a full length back and a paper cover behind the control door as well as non-conductive shaft on the front controls to protect the user. I do not know why a power transformer was used instead-I do not think the cost savings was that great.

Another example of what I think is a stupid way to design a set is a 1950 GE series string set that I have. They used the radio trick of wiring all the power supply grounds together and then coupling it to the chass via a resistor/capacitor network. Considering the labor used in tieing all the necessary components for a TV to the common internal ground, I think this design did not save any money over a power transformer.

I have two isolation transformers and always use them when repairing radios/tvs.

[andy]

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[wa2ise]

Originally Posted by nasadowsk

As for a live chassis TV? these days, I'm amazed - switching power supplies are so cheap to build it's amazing.

In a sense, half of a switching power supply is a "hot chassis" design. The line gets rectified, filtered, and there's high voltage high powered transistors being driven by an oscillator that switches current on and off into a high frequency transformer.

Any line operated device has to have some powerline wiring inside, and as long as that is well insulated via a plastic or wooden cabinet, it's not an issue. It's then an easy extension to just make the entire thing hot chassis, and if it's a self contained radio with internal antenna and speaker, and is completely surrounded by a non conductive cabinet, it is safe.

[Telecolor 3007]

The Swedish guys from "Luxor" also made electronics with live chassies, but don't know how they made the next thing: when you insterted the plug and the chassie should had 220 V on it, the apparatus didn't turn on!; in only turned on when the phase of the supply network isn't on the chassie!
In Europe, there where a lot of damn bloody live chassie tv sets (including color ones). The reason why: they sad the transformers are to expensive to built and the tv sets will be to heavy if they will put an transformers. The only ones that gave a shit about that stupidity where the Soviets - the Soviets always made tv's with transformer (there where a few models that had auotransformer - likw the one at my home - with autotransformer you could have a live chassie too!)
The 1st Romanian tv set (V.S. 43-611), made with French components had live chassie and metal case! I guess that in Japan they had live chassies sets too, since the Romanian tv sets (Naţional, Luchian, Grigorescu) where made with Japanese components and live chassies! On the oposite, allmost all Romanian tube radios made after 1949 had transformer (the only live chassies ones where made in the '50's, when D.C. was still found in some areas).
I heard of people dieing electrocuted by live chassie tv sets. A guy had 2 doughters. One day, one of his girls flipped a flower vase and the watter liked into the tv... the chassie was live, and she got electrocuted - she died The guy dumped the live chassie tv and he bough him a Soviet tv - the Soviet tv had a transformer. Some people died while tryed to repair these sets.
I will get me a Romanian Naţional V.S. 43-614 tv set (the 1st one to have Japanese components - made by "National-Panasonic" ("Matsushita")) - except for the C.R.T. - which was "Valvo"), whic have live chassie, but since it may also works at 110 V I will conect it to an 220 V - 110 V transformer, so there will be no direct conection to the supply network! I will also put an light bulb to see if there is current on the chassie.

[kx250rider]

Originally Posted by andy

That TV must have also had a defective antenna isolation block. No dangerous voltage should ever appear on the F connector regardless of which way the power line is connected. Even when the power is connected correctly, the chassis of a hot chassis TV still has a dangerous voltage on it, and needs to be fully isolated from anything the user can touch.

True in theory, but by the late 80s and 90s, the F-connector was common ground with the whole ground of the board, which was often connected to the neutral side of the line. Same deal on cable boxes and VCRs. The Sony TVs from the 70s also had the F-connector live. In fact, when I was working for a Sony shop in the 80s, there was a rule that you may NOT use the F-connector to feed the sets on the bench. We had to use a 75-300 ohm transformer and use the twinlead input. The boss got tired of buying SG-613s after a tech would blast the power supply by cross-polarize the TV with the antenna amplifier, which was in common with all of the other TVs on the bench. We did use isolation transformers on all sets being worked on, but not for bench-testing after repairs were finished. One of the worst cases I saw myself, was that I was in a customer's house, and the husband was trying to show me some sort of a hook-up problem he was having, and he laid the cable box ontop of the VCR... A big flash, and the house breaker tripped. The cable box and the VCR were welded together from one of the cable box's case screws and the metal case of the VCR. It was a Panasonic VHS machine from the 80s, and the cable box, if I recall, was a Zenith from the 80s. It also took out the power supplies in both units. Turned out that the customer had an old nonpolarized extension cord running into the wall cabinet where all this stuff was hooked up, and the VCR & cable box were reversed.

Charles

[yagosaga]

Hello,

I am repairing tv sets since 1973. The first non-life chassis I personnally saw was in 2005. It was an U.S. tv set... It was an incredibly exciting feeling to touch the chassis without being fried...

- Eckhard

[Tripod]

Hi

I was alerted to this problem by my tech who made this one safe. I'm not sure exactly what he did, but he also told me an interesting story about this little Mullard doorstop. A bloke in England got fedup with his nagging wife. One fine day, he replaced the grubscrew in the on/off knob with a longer one. When his wife switched the radio on, she was electrocuted. I'm not sure if this is an urban legend, tho'.

tripod

[andy]

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[Telecolor 3007]

Many people died in Romania trying to repaier live chassie sets!
I can use a protection transformer or a transformer if you want to have a set like this, in order to don't have the phase of the electricity network on the chassie.