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Old 2nd Jul 2020, 11:56 am   #1
winston_1
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Default Half wave mains rectification and live chassis in Australia and New Zealand?.

Recently came across on an electrical forum the fact that half wave rectification of the mains was not allowed in Australia.
Some quotes:

"While I do not know concerning the "Regulations" in the UK, any device which provides only "Half Wave" rectification is not allowed to be connected to the "mains" in Australia. However, if the Rectifier is only "Half Wave", the Mains supply will be "loaded" at only every "half cycle". (Power supply authorities do not like this - for rather obvious reasons.)"

"As far as I am aware, all (Cathode Ray Tube) CRT TVs sold in Australia had a "mains" transformer.
The "high voltage" secondary of these transformers was "centre-tapped" and the DC was obtained via a "full wave" rectifier, such as a 5Y3GT.
(Yes, I do know that anything less than 1000 V AC is "low" voltage, according to IEC definitions.)

Of course, later designs (and, probably, all colour TVs) utilised solid state components, including "Full Wave" (Bridge Rectifiers) but these always included a "mains" (isolation) transformer - for "safety" reasons - and the transformer was required to provide the "heater" voltage for the CRT."

"(This post has sent me back looking at books and manuals which I still have from the 1970s and before.
e.g. "Miniwatt Technical Data" 1958 and "The MAZDA Book of Pal Receiver Servicing" 1971.)"


I was quite surprised to read that as I thought UK sets were exported down under before the Japanese invasion. Does anyone have any more information on this and did this also apply in New Zealand?
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Old 2nd Jul 2020, 2:29 pm   #2
Dave Moll
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Default Re: Half wave mains rectification and live chassis

Presumably, this implied either that non-isolated chassis were not used or that they were all at half-mains potential after full-wave rectification.
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Old 2nd Jul 2020, 3:09 pm   #3
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Default Re: Half wave mains rectification and live chassis

I am not surprised that Oz has (had) problems with asymmetric current. A lot of places where and still are fed by Single Wire Earth Return (SWER) circuits, you don't want any DC on them otherwise bang go the earth spikes.

It is worth looking up SWER, a most ingenious system that is remarkably safe, cheap, and upgradeable.
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Old 2nd Jul 2020, 4:56 pm   #4
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Default Re: Half wave mains rectification and live chassis

Quote:
Originally Posted by merlinmaxwell View Post
I am not surprised that Oz has (had) problems with asymmetric current. A lot of places where and still are fed by Single Wire Earth Return (SWER) circuits, you don't want any DC on them otherwise bang go the earth spikes.

It is worth looking up SWER, a most ingenious system that is remarkably safe, cheap, and upgradeable.
I never gave it a second thought!
The US power system is somewhat different. Our earthing system is different, as well. There is so much half-wave retification used here for just about everything, so there is little concern.
Power factor is a different issue. Little concern in residential, but commercial and industrial has to have correction.
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Old 2nd Jul 2020, 6:51 pm   #5
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Default Re: Half wave mains rectification and live chassis

Surely SWER on the input-side of a "power-pig" transformer doesn't imply that the downside should necessarily have any issues with half-wave rectification?

Provided the half-wave-rectifiying downstream loads are [randomly and equally] doing their thing then the DC components they introduce will generally cancel-out and so not present any reflected DC component to the line?

I always thought that the UK's "Live and Neutral" polarised-power-plug mentality must have caused significantly and unnecessarily-excessive DC-components on the mains back in the days of half-wave rectification. Unpolarised power-plugs would have randomised the DC-component across the local phases and made life easier for the power-providers.
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Old 2nd Jul 2020, 7:12 pm   #6
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Default Re: Half wave mains rectification and live chassis

The Aussie electronics industry was surprisingly idiosyncratic and it's true that live chassis radios and TVs were very rare there, though I don't know if they were actually prohibited. There were technical reasons for this, but Australia was very protectionist throughout most of the 20th century despite the 'commonwealth preference' talk, and used what would now be called health and safety rules to discourage European and American imports. (Most countries were protectionist to a degree at that time of course, including Britain.)
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Old 2nd Jul 2020, 8:00 pm   #7
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Default Re: Half wave mains rectification and live chassis

The last section of this web page gives some information. One portable TV designed in Australia had a live chassis, the other live chassis sets were modified imports of UK and USA sets.
http://members.iinet.net.au/~cool386...n/foreign.html

One other point about USA TV sets was that many used voltage doubling for the HT line therefore using both half cycles. An interesting design was the use of, I think, the sound output valve to supply lower HT to parts of the set requiring lower voltages. The sound output anode was supplied by the higher HT and the cathode circuit fed the lower voltage part, well decoupled.
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Old 2nd Jul 2020, 9:25 pm   #8
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Default Re: Half wave mains rectification and live chassis

SWER is indeed used in Australia, but only for the high voltage supply into distribution transformers.
Half wave rectification of the mains would have no effect on the high voltage circuit feeding the power company transformer.

It would however adversely affect the transformer itself, DC current through the low voltage side of the transformer would tend to saturate the core and result in extra heating and losses.
A small transformer for a single household would be more vulnerable than a large one in a built up area.
But we have single transformers for isolated homes here in the UK, and no one worries.

Of greater concern would be higher loading appliances with half wave rectification. Hair dryers and the like. I suspect that no one has realised that these are sold worldwide including presumably in Australia.

There is somewhere a now long closed thread in which I enquired about the effects of half wave rectification on power company transformers.
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Old 2nd Jul 2020, 10:25 pm   #9
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Default Re: Half wave mains rectification and live chassis

Quote:
Originally Posted by paulsherwin View Post
The Aussie electronics industry was surprisingly idiosyncratic and it's true that live chassis radios and TVs were very rare there, though I don't know if they were actually prohibited. There were technical reasons for this, but Australia was very protectionist throughout most of the 20th century despite the 'commonwealth preference' talk, and used what would now be called health and safety rules to discourage European and American imports. (Most countries were protectionist to a degree at that time of course, including Britain.)
We tend to forget how powerful were these ‘non-tariff’ barriers to trade. They’re still around, though attenuated compared with 30-40 years ago. Needless to say, they tend not to enter politicians’ thinking because they’re technical and difficult.

We tend to think particularly of the old challenges of stringent German DIN and IRT specifications, but in many ways competing with Australian products was just as difficult, particularly those from the mighty AWA, who embraced practically all electronic markets, from consumer to industrial to broadcast. As we know, all design involves compromise, and Murphy’s law would guarantee that the AWA designer adopted a different set of compromises from one’s own (often apparently regardless of cost!). Competing with that situation was tough.

However, we have to thank Australian technical independence for the wonderful work of Fritz Langford-Smith (of AWA) and his splendid authoritative ‘Radio Designer’s Handbook’ which so many of us keep close at hand.

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Old 3rd Jul 2020, 12:26 am   #10
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Arrow Re: Half wave mains rectification and live chassis

Quote:
Originally Posted by merlinmaxwell View Post
It is worth looking-up SWER: a most ingenious system that is remarkably safe, cheap, and upgradeable.
Having never heard of 'SWER', I 'looked it up' at Wikipedia . . . .
https://en.wikipedia.org/wiki/Single-wire_earth_return.

I found that write-up to be really interesting.

Al.
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Old 3rd Jul 2020, 12:36 am   #11
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Default Re: Half wave mains rectification and live chassis

This issue was discussed previously in this thread: https://vintage-radio.net/forum/showthread.php?t=159413.

The objection to the use of AC/DC receivers with half-wave rectification came from not from the local setmakers (some of whom wanted to go that way), nor from the electricity suppliers, but from the water supply authorities, who found that the resultant stray DC earth currents caused significant corrosion of underground pipework. This was based upon measurement, not assumption. The supposition that it originated as a non-tariff trade barrier is not supported by the available evidence. That argument seems to be commonly invoked in cases where the destination country regulations differ from those of an exporting country, sometimes I think before any analysis is done as to why there are differences. That regulations differ is hardly surprising. There are usually multiple satisfactory solutions to any given engineering problem, and that chosen will often depend upon local circumstances, preferences, etc. In some cases the differences might also turn out to be hurdles to trade, but that does not mean that they were originally installed with that intention. For example, the effective division of world electricity supplies into 50 Hz and 60 Hz areas is a barrier, although less so these days, but arose not because of a desire to create a barrier, but from the separate deliberations – and outcomes - on the question of optimum frequency.

Given that Australian electricity distribution coalesced on the MEN system, I think following the NZ lead, where it had been standardized in 1920, then non-negligible earth currents did exist as a matter of course, and I understand the more so with the commonly used overhead distribution. The MEN system, with a neutral-to-earth connection and earthing point at each consumer’s premises had been adopted with good reason, namely poor ground conductivity in many locations.

Whether or not the MEN system and its consequences, including the need to minimize DC earth currents - was idiosyncratic I think depends upon one’s frame of reference and comfort zone. From the UK perspective, it may well look that way. But turning the telescope around, I found that the UK use of clunky three-pin plugs incorporating fuses to be rather odd at first, until I understood the reasons – including the use of ring mains - for so doing. And I thought that the NZ earthing requirements were pretty strict, until I was living in Texas and had a house built. There its was required that just about everything, including the neutral, be bonded to the grounding stake, including incoming utilities (telephone and cable TV) and the TV/FM antenna structure and coaxial cable outer. One could have a separate RF ground stake for HF receivers, but it had to be bonded back to the main ground stake. One reason was that in an area of intense electrical storms, kV potential differences could exist between ground points separated by just a few metres. I surmise that DC in the ground currents was less of an issue because the split-phase system would result in much cancellation, even at individual consumer level, hence the acceptance of AC/DC equipment..


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Old 3rd Jul 2020, 1:18 am   #12
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Default Re: Half wave mains rectification and live chassis

The comment about all solid state sets in Australia having a mains transformer is a furphy, having been bitten once or twice in the 90's repairing sets where some had replaced the aerial socket with a none isolated one, subsequently emitting showers of sparks while connecting the aerial lead and tripping the safety switches.
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Old 3rd Jul 2020, 6:50 am   #13
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Default Re: Half wave mains rectification and live chassis

Hi Terry,
I read somewhere that the TV repair trade in Australia generally didn’t like the live chassis TV’s and if asked would try to steer the purchaser towards fully isolated sets.
Do you know if this is correct or a “Trade Tale”.
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Old 3rd Jul 2020, 11:01 am   #14
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Default Re: Half wave mains rectification and live chassis

cannot speak for Aussie but I do know that here in NZ there was often a large gap between the wiring regs and what actually happened - e.g. people happily wired up their own places and some suffered from the results - so it would not surprise me if some imported live chassis sets either ignoring or unaware of the regs.
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Old 3rd Jul 2020, 11:03 am   #15
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Default Re: Half wave mains rectification and live chassis

The other thought is that a lot of immigrants from the UK to here and to Aussie brought along their own household electrical goods as they could be quite pricey - so that's another avenue as there were no inspections.
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Old 3rd Jul 2020, 11:42 am   #16
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Default Re: Half wave mains rectification and live chassis

Quote:
Originally Posted by Nuvistor View Post
Hi Terry, I read somewhere that the TV repair trade in Australia generally didn’t like the live chassis TV’s and if asked would try to steer the purchaser towards fully isolated sets.
Do you know if this is correct or a “Trade Tale”.
Money was money, live chassis or not and I didn't have nor knew of anybody else that had problems servicing live chassis sets.

One of the workshops I worked in had over a dozen techs and we all worked on live chassis stuff.

Wracking the brain to recall anything that had a transformer in it other than the earlier solid state stuff is drawing a blank

There probably was some, but it would definitely have been in the minority.

As for sales of sets, well the salesmen told all sorts of to get a sale.

I think you'll find it was more of a fairy tale than actual fact.
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Old 3rd Jul 2020, 11:47 am   #17
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Default Re: Half wave mains rectification and live chassis

Thanks Terry,
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Old 3rd Jul 2020, 6:12 pm   #18
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Default Re: Half wave mains rectification and live chassis

Whatever the reason might have been, even the penny pinchers at Philips went through the trouble of redesigning the non-isolated buck converter powersupply of their 1972 K9 colour sets for the AU/NZ market to use an isolation transformer instead of just a coil. Basically the same circuit, I think, but slightly more expensive to manufacture.
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Old 4th Jul 2020, 10:00 am   #19
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Default Re: Half wave mains rectification and live chassis

Quote:
Originally Posted by paulsherwin View Post
The Aussie electronics industry was surprisingly idiosyncratic and it's true that live chassis radios and TVs were very rare there, though I don't know if they were actually prohibited. There were technical reasons for this, but Australia was very protectionist throughout most of the 20th century despite the 'commonwealth preference' talk, and used what would now be called health and safety rules to discourage European and American imports. (Most countries were protectionist to a degree at that time of course, including Britain.)
Those trade 'barriers' could be quite helpful. The Co. I was working with made studio mixers and at the time the only comparable item was from Rupert Neve imported from the UK. Since we were making a comparable item, we managed to get a 20% import duty on the Neve stuff!
The only thing that got my goat in Australia was the fact that (in theory) I was not allowed to do house wiring although I was considered competent to design and install a 3Ph power supply for a TV transmitter. I got over the wiring regs when we moved to the bush and having my own generator, was deemed to be the electricity 'authority'!
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Old 4th Jul 2020, 10:15 am   #20
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Default Re: Half wave mains rectification and live chassis

Quote:
Originally Posted by lesmw0sec View Post

Those trade 'barriers' could be quite helpful. The Co. I was working with made studio mixers and at the time the only comparable item was from Rupert Neve imported from the UK. Since we were making a comparable item, we managed to get a 20% import duty on the Neve stuff!
Hmm....so it was you was it?

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