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Old 2nd Sep 2019, 2:31 am   #1
Synchrodyne
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Default AC-DC Live Chassis Receivers in the Antipodes

From the thread: “Valve Items - Philips/Mullard Rimlock-to-Noval Transition”, https://www.vintage-radio.net/forum/...00#post1172700

Quote:
Originally Posted by joebog1 View Post
As far as this goes, and only slightly off topic, I have NEVER even seen an AC/DC radio in my life. There were a few early B/W TV sets that were, but I have never worked on one. I think this may have to do with Australian regulations, but I cant prove that. We do have an excellent record for electrical installation however.
This I think justifies a separate thread.

Some information on the Australian aversion to AC-DC chassis is provided on this article from Electronics Australia (EA) 1975 August:

EA 197508 p.64.pdf

The major concern was that such receivers would put DC back on the mains, and that with the MEN distribution system by then common in Australia, this would cause DC earth currents of sufficient magnitude to cause significant corrosion in underground pipes and other apparatus. So the supply authorities said “no” to colour TV receivers with AC-DC chassis. Evidently with the advent of colour, there was renewed interest in using AC-DC chassis by some of the manufacturers. Philips might have been amongst this group. That was at least hinted at in an EA 1974 September article on the Australian version of the K9 model, whose European prototype was of the AC-DC type. On the other hand, the engineering required to include a transformer-isolated power supply had already been done for the NZ version of the K9, so it was easy enough for Philips to do the same in Australia.

The safety issue, at least from the end-user viewpoint, is an interesting one. The perception of what is safe and what is not does seem to vary from one country to another, and Australia and NZ have leaned towards a more rigorous approach than some others. It might be possible to build an AC-DC chassis that meets Class II requirements. But that did not seem to be the case during the valve era. At least from what I have seen, a typical British AC-DC radio receiver of the 1950s had a back panel with multiple ventilation slots. Although these were sized and placed so that it was near-impossible to touch the chassis with a finger, it was very easy to do so with a metal knitting needle, which was a commonplace household item of the time. Also, the aerial and earth sockets/connections, and the gramophone pickup input sockets, where fitted, were isolated from the chassis by a single capacitor in each case, so that a single failure could result in a live socket. A better way would have been to use isolating transformers, RF for the aerial/earth, and AF for the gramophone. The output transformer provided isolation for the external speaker sockets, where fitted, but a fully isolated secondary made it not so easy to include it [the output transformer] in the feedback loop. With a 230-volt electricity supply, I suspect that this kind of AC-DC chassis might have been deemed to be “unsafe at any speed” in the antipodes.

Here in NZ, AC-DC radio receiving equipment was rare, and I suspect for the same reasons as in Australia. NZ adopted MEN distribution (3-phase, 4-wire, with neutral solidly bonded to local earth at each consumer main switchboard) as standard way back in 1920, and there could have been very few installations that did not conform. I have heard anecdotally that some supply authorities frowned upon or even banned AC-DC equipment. Given the Australian experience, that seems to have been quite likely. I think that by the time colour TV arrived in NZ (1973), the rules required that domestic appliances be either Class I or Class II, with Class 0 (AC-DC) and Class 0I appliances prohibited. (Class 0I was Class I in which the protective earth lead was not incorporated in the power lead and its plug, but was separate and required separate connection to a suitable earth point, which meant that the appliance was easily used in the unearthed state.)


Cheers,
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Old 2nd Sep 2019, 3:18 am   #2
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

I think you're right about the colour TV. Though never sold in the UK, Philips' first transistorised colour TV chassis (K9) which first appeared in 1972 and was rolled out in various other factories in 1973 was a global design and as such adapted for local production for the AUS/NZ market as well. The simple but quite reliable uninsulated buck converter power supply unit was modified to provide mains insulation for those markets.
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Old 2nd Sep 2019, 3:34 am   #3
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

Thanks to Synchrodyne for the clarification.
Its interesting to note that Australian electrical installation rules are actually labelled
AS/NZS 3001:2018 was reviewed and updated only last year ( 2018). I did not know that the MEN system was introduced in 1920!! Im NOT quite that old yet . Australia and New Zealand share the same ( safe ) rules.

I do well remember figure 8 cable being used on almost every radio that I have seen going way back. Earth being provided by the antenna earthing system, which in my experience was never used. Even a nice set with an RF stage generally had a "bit o wire" nailed into the picture rail, or just hanging out the horrible press spring post that most used. SOME had nice brass nickle plated spring posts, but as sets became cheaper they then became self collapsing bakelite.
I have repaired many hundreds of Fender amps over the years, and they contain a wonderful little death cap. US mains doesnt have earth ( that I know of ) and to prevent hum they had a switch so one could switch either active or neutral to ground. ( I remove this little death trap on sight) The cap was usually a moulded paper rated at 400 volts, and as far as I know was never uprated for export models. Perhaps that slightly OT.

Australia has had ELCB ( thats what they used be called : Earth Leakage Circuit Breaker) since the 80,s, and now any house connected to the mains must have "safety switches ) (todays name for ELCB ) fitted before the electricity supplier even hooks your house into the grid. Interesting to note : Today the wire from post to house belongs to the house and its the house owner that needs supply that bit of feeder. Only a few years ago that was supplied by the electricity company, and they did very vigorous megger tests before connecting their cable.
Electricity supply companies back then had substantial copper wire to feed the house, and was hard drawn copper with very hard PVC insulation.
Today its quite thin aluminium wire, and is about half the guage it used to be.

On a big house it was four strands of bare copper of minimum 16MM^2
isolated on the necessary glass or porcelain insulators.
Today its 4 aluminium conductors insulated with hard PVC, and lightly twisted together. No catenary wire is used however !!.

Just my observations, even if it is off topic to some degree.

Joe
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Old 2nd Sep 2019, 4:27 am   #4
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

AC/DC sets from the mid 1930s thru to 1940s were/are not uncommon in Australia. Most manufacturers listed in the 1938 Radio Trade Annual of Australia had "Universal" or DC models.
By the late 40s and 50s this had changed and it is a truism that you don't see the live chassis sets in the late 40s onwards which were so prevalent in the UK & USA markets.

It really is more a case of location, location, location as to whether you come across any/many AC/DC sets in Australia.
I've got a garage loft full of Philips sets with C type valves and bulbous Barreters!

Every town outside the Perth Metropolitan area where the mains was 250 volts 40 cycles only had DC 220v mains from local generators. It was only in late 38/39 that AC mains replaced DC in Albany and was gradually introduced into other towns over the next decade(s). I believe, It was a similar story in rural South Australia. Whereas DC mains was most definitely the exception in the more populous states of NSW, VIC & QLD.

So yes by the 50s AC/DC sets were not common or popular but most definately AC/DC sets were produced as a necessity in the 30s and 40s.
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Old 2nd Sep 2019, 7:19 am   #5
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

The attached Electronics Australia 1986 January article covers the final switch-off of Sydney's remnant DC distribution system. At the end the author details his view of AC/DC radio receivers.

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File Type: pdf EA 198601 Sydney DC Switchoff.pdf (588.2 KB, 122 views)
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Old 2nd Sep 2019, 10:45 am   #6
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

A bit dramatic though. The last mains non-insulated TV sets even made it into the early 1990's in other parts of the world.
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Old 2nd Sep 2019, 10:52 am   #7
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

I suspect there was an element of protectionism in the Aussie aversion to transformerless sets. It discouraged cheap imports from Europe and North America, and forced foreign companies to run Australian factories building specific designs for the local market.
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Old 2nd Sep 2019, 11:38 am   #8
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

Quote:
Originally Posted by joebog1 View Post
Electricity supply companies back then had substantial copper wire to feed the house, and was hard drawn copper with very hard PVC insulation.
Today its quite thin aluminium wire, and is about half the guage it used to be.

On a big house it was four strands of bare copper of minimum 16MM^2
isolated on the necessary glass or porcelain insulators.
Today its 4 aluminium conductors insulated with hard PVC, and lightly twisted together. No catenary wire is used however !!.

Joe
Fascinating to see how power distribution techniques differ between different countries. I gather that Australia makes quite a bit of use of 'single-wire earth return' overhead distribution lines, something that's entirely unheard-of in the UK!

As to the overhead distribution run from the transformer/substation along streets and the 'final drop' to houses, yes here in the UK we are seeing more and more of the uninsulated-wires-on-porcelain-insulators being rapidly superseded/replaced by what's known as ABC - Aerial Bundled Cable -

http://www.caledonian-cables.co.uk/p...es/al/lv.shtml

which is joined/tapped-into using a bolt-down insulation-displacement-system.

As to AC/DC technique - was there ever much domestic DC mains in Australia/New Zealand? DC generation/distribution continued in some parts of the UK until the 1960s, predominantly in industrial/mining areas where 'the big factory' or "the pit" had its own DC generating plant. AC/DC meant the manufacturer could just supply one radio/telly range, with obvious production cost-savings - and purchasers weren't faced with their electronics becoming useless once the National Grid hooked the area up to AC.
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Old 2nd Sep 2019, 11:52 pm   #9
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

I was completely unaware that Australia EVER had DC mains until Red Duck pointed it out.

I did know that Western Australia had (or maybe still does) have 260 volt AC mains where the rest of the country has 240 volt AC. In every house I have lived in, and every workplace I have been in, it's been almost spot on at 250 volts AC. As far as frequency goes a synchronous clock almost never needs resetting. Also spot on @ 50 Hz.

I have never been to Western Australia so I have no experience with that state, so I'm only quoting what I have read.

Synchrodyne also has posted more information. I had given up reading Electronics Australia by that date as its technical writing had diminished considerably by then, and most of its projects revolved around semiconductors.

Joe
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Old 3rd Sep 2019, 9:39 am   #10
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

Hi Joe
Perth switched from 40 to 50 cps mains only in 1958. Mains voltage in Western Australia was decreased from 250 to 240v sometime in the late 80s or 90s.
Prior to 1946 there was no interconnection between country towns and they all had their own power house. Post '46 the government started building an interconnected network and gradually replaced/shutdown the old DC generators.
So courtesy of geography I got more than my fair share of old AC/DC sets.
Some photos attached of an STC console (~1938) which had been delivered to a country town and converted for DC mains with an STC conversion kit (barreter, dropper resistor for valve heaters and choke for HT) by the local radio shop.
I had a spare transformer and converted it back for AC operation. Which was essentially going from series to parallel wiring of valve heaters,earth connection had been isolated from chassis by a capacitor.
The magic eye - a 6T5 (which are now unobtainable) - still had life in it. Probably due to the set running on 220v DC for many years.
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Old 3rd Sep 2019, 10:17 am   #11
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

I'm not quite clear how AC/DC sets would "put DC back on the mains" [post 1*] but then my knowledge of mains distribution is at zero potential

It seems that the history of DC mains [followed by AC] in Australia [Red Duck post4*] was not so dissimilar to that in the UK except that one country was relatively new and building up it's infra-structure as opposed to having it bombed out in Europe. This would explain why the UK continued needing to meet the requirements for different mains supplies in different areas across the country. There would be economic factors applying too, well in to the sixties eg a Mains Transformer was probably the most expensive component and doing without it would help to make domestic goods more affordable when we were being told that we'd "never had it so good" circa 1963. On top of this I suspect that Paul's comment about protectionism [post7*] possibly being a factor influencing a quicker reduction in AC/DC goods at the Antipodes may be correct!

As for the safety factors with AC/DC equipment knitting needles etc, it is possible that Health and Safety Officials would be committing suicide en-masse these days but different times, more respect for electricity and commonsense being applied seems to have worked. I have never come across any report of a domestic fatality or injury although this may have been a factor in the workshop environment. Working conditions were usually pretty "shocking" in the Trade [from what I read].

The late, great Chas Miller told the story of two elderly ladies who plugged in a TV set up for AC but they were on DC Mains. When it began to smoke and smoulder, they poured in a bucket of water for good measure but they survived!

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Old 3rd Sep 2019, 10:35 am   #12
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

It's the necessarily half-wave rectification used that puts the DC component in- perhaps if every set used twisted, unmarked pair mains flex there would (statistically) be net cancellation of DC component on the AC supply, but only half (again statistically!) would work first time when connected to DC, the others would need plug wiring reversal.... So, mains leads were marked red and black (or whatever code a particular territory had adopted for line and return) and folk assiduously wired accordingly, many into 3-pole or otherwise polarised connectors and the DC component aggregated.

As well as the protectionist aspect mentioned (as my brother puts it, everything in human history boils down to economics....), would iron and copper for transformers have been relatively less expensive in Australia? I know it's got loadsa iron ore (and coal for the processing thereof), but not sure about the copper.

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Old 3rd Sep 2019, 10:41 am   #13
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

Quote:
Originally Posted by dave walsh View Post
I'm not quite clear how AC/DC sets would "put DC back on the mains" [post 1*] but then my knowledge of mains distribution is at zero potential
Because the radio/tv etc has a rectifier.

Lawrence.
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Old 3rd Sep 2019, 11:16 am   #14
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

Yes LOTS of copper. Mt Isa Mines is predominantly copper. I dont know wheather it was our processing, or the quality of the ore, but Mt Isa copper is exceptionally pure and of low resistance. Years ago ( when I learned to design and make transformers) Australian winding wire was the best obtainable. ( read: probably because we didnt need pay freight)

To red duck: That was once a very nice electric wireless!! Even an RF stage, which wasnt common in eastern states. Its a pity it was stored in the shearing shed ( maybe the grain barn ) but I cry to see that tuning capacitor so corroded. It even looks like an Aegis brand cap. 10 - 415 pF if I remember correctly. 455 Khz IF stage.
I am guessing that whacking great big "valve" next to the transformer is the barreter.
I have never seen one "in the flesh".
RF stages also were quite rare. I guess most of the radios I saw as I grew up were made in Sydney, which also had LOTS of radio stations. I have fallen out of quite a few gum trees tying up wire to receive 2SM, the local rock station in Sydney. Which by the way was roughly equivalent to "channel radio" But of only ever seen the Goodies version of how that happened.

Only slightly off topic, but here goes.
Dad worked on T1 power station. Its one mile underground ( to walk in ) and located very high up in the Snowy mountains, ( You enter from Cabramurra somewhere. Australias highest town ) and the 3 phase cables ran from there to Melbourne. It used to be 330 KV.
I worked on the digitisation of Rowville power station in Melbourne, and those SAME cables my dad worked with now carry ONE MILLION volts to Melbourne.

https://www.exploroz.com/places/1031...-power-station

Joe
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Old 3rd Sep 2019, 12:40 pm   #15
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

Quote:
Originally Posted by ms660 View Post
Quote:
Originally Posted by dave walsh View Post
I'm not quite clear how AC/DC sets would "put DC back on the mains" [post 1*] but then my knowledge of mains distribution is at zero potential
Because the radio/tv etc has a rectifier.

Lawrence.
More significantly - an AC/DC radio or TV has a HALF-WAVE rectifier.

So, the positive half-cycles supply more current than the negative half-cycles. This leads to greater voltage drops in one direction in a distribution cable than in the other direction - there is therefore a DC bias.

AC-only equipment also has a rectifier, but it is almost always a full-wave rectifier, so current flow in positive and negative half-cycles is the same, and this asymmetric bias does not occur.
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Old 3rd Sep 2019, 12:59 pm   #16
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

When I first started in the trade it was all half wave rectifier for TV's, later on it was half wave for heaters too, usually -ve which made it more mains friendly.

The bridge rectifier came in later which meant we only got a belt/2

Lawrence.
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Old 3rd Sep 2019, 1:10 pm   #17
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

Yes I understand half wave rectification chaps but thanks for the fuller explanation of a DC bias being created. It was just that I didn't realise it was that simple in terms of National Power Suppliers-the heavy lifting as it were I couldn't see how the Electrical Engineering ie MEN distribution with a bonded local earth could be so vulnerable to the presence of domestic sets. If the concern was simply the half cycle product of rectification from AC/DC equipment wouldn't it take a lot of them? Did problems actually arise and if so, was it just the sets, local wiring or a different regulatory perception perhaps? Maybe we are just back to finding an excuse to apply Trade Protectionism? It's all a bit fascinating and new to me, certainly justifying a separate thread as synchrodyne [great ID] said in the first place.

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Old 3rd Sep 2019, 1:20 pm   #18
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

On the continent, most colour TV sets were AC only but still with a live chassis. Some used AC for the valve heaters, some used one half of the waveform for the heaters and the other half for the +B. Still others used full bridge rectifiers (Philips K8 and later; increasingly more common in other brands during the 1970s). Sets with a full bridge rectifier could theoretically operate on DC mains, but apart from the degaussing, the mains switch would also have posed a problem.
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Old 3rd Sep 2019, 1:35 pm   #19
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

I didn't know that either Maarten-very interesting. Overall I suppose the biggest concern re AC/DC circuitry these days is people trying to restore equipment "by sight" who may have no understanding of live chassis issues

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Old 3rd Sep 2019, 8:01 pm   #20
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

The cynic in me thinks that Australia and New Zealand requiring power transformers in their sets probably had about as much to do with personal safety and network integrity, as British manufacturers managing without them had to do with the ability to operate on a DC supply.

Which is not to say it wasn't an absolute master stroke on both sides .....
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