ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Interesting flash-game - wire the plug

Basic european regulations require that *ALL* appliences function safely with either polarity. Polarity in almost all European systems is random.

Btw, I noticed European TVs still tend to have a physical switch (button) on the front while a lot of US TVs have software switching only.

Why is this?

A switch for what? If you mean power, some sets do/did have a main on/off, but genreally the standbys are left on for the benefit of a remote control.

There were a few sets here in the 1970s (can't remember what make) which actually had two main switches, the second one being located out of the way on the side of the set. (And both actually turned off everything, including the remote-control circuitry, if present).

There seemed to be an obsession with making sure that TV sets were always completely isolated from the supply when unattended at the time.

People were often urged to unplug the TV completely when going to bed at night, as this public information film demonstrates:

Bedtime Fire Routine, 1979

(Approx. 2.8MB, Real Player needed.)


{ Edited for altered URL on link }



[This message has been edited by pauluk (edited 07-19-2005).]

Virtually all Australian made TV sets had an earthed, transformer isolated chassis. There were very few using the European live chassis series heater approach as this was disliked intensely by the servicing trade. Further, the half wave rectifiers used in these sets put DC onto the mains which didn't go down too well with the supply authorities.
There was no actual need to make sets this way as DC mains had been all but phased out by the time TV arrived here in 1956. Apart from a small section of Sydney's CBD, DC mains was never used in the capital cities.
Further details on set design for those interested are on my site: http://www.users.bigpond.com/cool386/ekco/ekco.htm

With the advent of colour (and imported sets) during the mid 70's, there were a number of European and Japanese made sets with a non isolated chassis, so Aussie technicians had no choice but to get used to the idea. Fortunately, most of the larger set manufacturers like Philips and National (Panasonic) who were assembling locally, continued to give us isolated power supplies with their Australianised models, but a few like Sony and Sharp didn't. With many sets this was nothing more than a 240:240V (for the UK designs) or a 240:115V (for the Japanese sets) isolating transfomer bolted to the bottom of the cabinet. Philips modified their switchmode power supply so that it had isolated secondaries (the Europeans had an autotransformer in their version).
Common among some Japanese sets were two power switches. One was the normal on/off switch usually combined with the volume control. Hidden away under a control flap was the other switch which disconnected the set from the mains. The reason? The user's on/off switch only disconnected the transformer winding feeding the DC supplies of the set. A second pole on the switch in the CRT's heater supply switched over from the 6.3V winding to a tapping of about 4V to leave the heater warm(some used a resistor or diode to drop the voltage in standby instead). This way the set had an "instant on" feature.
With the flood of Chinese sets in the 80's, live chassis became common, and with bridge rectifiers the chassis is live regardless of mains plug polarity. I've seen some horrifying instances of headphones connected to these sets, or the aerial isolation capacitors bypassed (damaged aerial socket), by unknowing people. And yes there have been electrocutions.
Nowadays, with the requirement for external speakers and AV sockets most are now using isolated switchmode power supplies, though classing them as double insulated appliances seems to be a bit optimistic.

That Ekco set makes for some interesting comparisons. I hadn't realized that Australian models didn't usually use the transformerless, live-chassis approach.

In mid-1950s England there were quite a few urban areas in which the older districts still had their original 3-wire DC distribution systems, so there was certainly a call for DC-operable sets -- Radios as well as TV.

The halfwave rectifier supplies did cause some problems in heavily populated AC areas though. I remember reading a piece in one of my old magazines which said that a certain electricity board was concerned over the assymetric distortion on the network caused by the sheer number of TV sets all pulling power on one half cycle.

There would still have been plenty of sets running on a reversible two-pin plug at the time, and even some on polarized 3-pin plugs with line/neutral reversed if they'd been in a DC area on the negative pole previously, but with 3-pin plugs becoming the norm, the majority of sets would undoubtedly have been pulling B+ power on just the positive half-cycle.

Going back to that Ekco design in general, the U.K. had only system A (405-line) broadcasts in the 1950s, with the associated AM sound and positive video modulation, so obviously there are quite a few other aspects of the design which differ.

How many of the Australian VHF channels were actually assigned at that time? Was it just the Band I channels, or were you already using those which were in what is now the FM broadcast band?

It also appears from the schematic that this Ekco has provision only for a 300-ohm twin feeder for the antenna. In Britain, the Belling-Lee 75-ohm coaxial socket was already the well-established standard.


By the way, for anybody who tried the "Bedtime Fire Routine" link above, the URL has changed. I've edited the link, so it should work now.

I've often wondered how the mains coped in the UK during peak viewing times with huge chunks of current taken only in the positive cycle. Colour sets would have been worse, and with more 3 pin plugs being used by the time they appeared in 1967 it must have had an effect.

We had 10 VHF channels to start with in Band 1 & 3, operating on 625 lines & 5.5MHz sound IF as used in parts of Europe. In fact, Australia was the first place outside Europe to use this standard, now known as "system B".
Then, in 1961 it was decided that ten channels was not going to be enough for the expansion of TV into rural areas. So, three extra channels were added; designated 0, 5A, and 11. They were given these designations so the channel numbers on existing sets in capital cities would stay as they were. This was to prevent confusion to existing viewers and so stations wouldn't have to change their logos. (In Australia the viewing public knows TV networks by the channel number they transmit on).
In order to fit these extra channels in, they were put in Band 2. For here in Australia, there was a very anti FM movement by the existing commercial AM broadcasters and our excessively conservative PMG (Postmaster General) Department. There was only an "experimental" FM service run by the ABC (our government broadcaster, equivalent to the BBC) which was merely a simulcast of existing AM programs. It was shut down in 1961. Not until 1974 would Australia have FM radio again. As a side issue, given the FM band had been allocated to TV, it was proposed that if and when FM radio started up again it would be on UHF. Local industry would have loved this captive market! But with the amount of imported FM receivers in Australia by 1974, the UHF idea was canned and FM radio simply coexisted with the TV channels in the 88-108MHz band.
With FM radio really taking off in the 80's, all new TV channels were placed in the hitherto unused UHF bands 4 and 5, and areas near capital cities using Band 2 TV channels were also gradually shifted onto UHF.
300 ohm balanced transmission line was standard from day one. I suspect this was because our TV practice largely followed the US (in the monochrome era). In fact many of our sets were based directly on US designs but obviously with changes to the IF and channel frequencies. We therefore had a mixture of American and European valves in our sets. Also, as our transmissions were all horizontally polarised there was no need to use 75 ohm coax. The negative modulation system with FM sound also has less of an interference problem. (Having said that, it's a shame the 405 line system was shut down in the UK...the simplicity and economical use of bandwith had a lot going for it)
It is interesting to note the UK tended to favour separate band 1 and 3 aerials with a diplexer for 405 lines; whereas here it was always one multiband aerial. I don't know if that's in part due to our transmitters always being co sited for any given service area. Nevertheless, we did have some UK aerials of the "Antiference" brand (later produced by the local Hills Industries company). Most aerials were US designed "Channel Master" though.
Coaxial cable and those wonderful Belling Lee plugs didn't really come into fashion until the mid 70's. A lot of the public were duped into buying new aerials and transmission line when colour started, even though most didn't need to.
These days 300 ohm ribbon is seldom seen except on old installations that have survived away from the coast. It's virtually impossible to buy new any hardware for it such as mast standoffs, but I do prefer it for low loss on UHF. Even the Belling Lee plug has its days numbered with the US style F connector being preferred for new installations; especially for digital TV.