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Old 4th Sep 2019, 12:32 am   #21
Synchrodyne
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

As I see it, the evidence so far available is not really supportive of the protectionism argument. The EA article attached to the opening post made it clear that when the emotive aspects were stripped away, the heart of the matter was that the electrical supply authorities did not want the non-negligible DC currents fed back into their supply systems that would derive from the widespread use of transformerless TV receivers. There was some quantitative data on this in the article. At the time, there was nothing to stop the import or local manufacture and subsequent sale of transformerless receivers. The risk for the buyers of such receivers was that some electricity supply authorities would ban such receivers from use on their networks.

Also, it was not a case where all local manufacturers were using transformers whilst some importers or would-be importers were not. Some of the local manufacturers also wanted to offer transformerless TV receivers.

The electricity supply authorities were essentially disinterested parties when it came to the question of the origin of appliances connected to their network. They had a technical argument, supported by actual measurements, against transformerless colour TV receivers from any source. I haven’t seen any rebuttal of that argument, and it could be inferred that at the time, the setmakers and importers who were in favour of transformerless receivers were unable to provide a persuasive rebuttal.

It was the supply authorities, not the local manufacturers, who made representations to the Government to restrain both the importing of and local manufacture of transformerless TV receivers. That adversely affected not just importers, but also those local manufacturers who otherwise would have opted for the transformerless approach.


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Old 4th Sep 2019, 3:05 am   #22
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

Quote:
Originally Posted by G6Tanuki View Post
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!
Single Wire Earth Return (SWER) was developed by Lloyd Mandeno in NZ in the 1920s for back-country electrification. (See: https://www.delahyde.com/tauranga/pa...47_Address.pdf.) Australia might have become be the biggest user, although it SWER is also used elsewhere. I noticed that is quite common in Canada. In some cases there it appears that two wires are used, the second being mounted on the poles about a couple of metres below the main wire, without any significant insulation. A look at the installation in the wildlife park a bit north of Whitehorse, Yukon showed that the second wire was connected to earth by a downlead at about every 5th pole. I’d guess that the second wire was added in areas of very poor ground conductivity.

Quote:
Originally Posted by G6Tanuki View Post
As to AC/DC technique - was there ever much domestic DC mains in Australia/New Zealand?
There was not much DC in New Zealand. The early adoption of 400/230 volts 50 Hz three-phase four-wire MEN distribution meant that most non-standard schemes, whether AC or DC, were not that large and were converted to standard before WWII. Auckland central was an exception. That had a fairly large DC distribution system that was not fully replaced until the late 1950s. The decision to replace DC with AC was made in the 1920s, but conversion work was suspended during WWII, at which time about 150 route-km was left. Wellington and Christchurch had DC systems that also survived into the mid/late 1950s, but in later days (post-WWI at least) these were special purpose supplies, for elevators, dentists’ drills, etc., with standard AC being available in the DC distribution areas.

Whether AC-DC radio receivers were offered for use in Auckland central during the 1950s I don’t know. I have never seen one from a local manufacturer, not have I ever seen any reference to this type being offered by local manufacturers. One might expect that had there been a market for AC-DC receivers, Bell would have offered an AC-DC version of its famous Colt model, but none of the information I have seen evens suggests that such existed. Conceivably those who lived in the Auckland central DC area were advised to use dry-battery table radios, or those with vibrator power packs that would allow operation from accumulators.


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Old 4th Sep 2019, 5:35 am   #23
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

Yes we had lots of SWER lines in Australia, Hateful, horrible things!!. 400 to 450 volts at any single time. Impedance measured in the ohms range. Noisy as anything imaginable.
Yes one could run a welding machine, while subjecting all other users to a "musicolour" light show as the volts went up and down with the welders skill.
They still very much exist!! After all a 10,000 square mile cattle station will be some ways from the grid. Most stations these days have largish solar systems with battery backup. I have fitted many my self. The "genny" usually an ultra leaky green painted Lister diesel picks up the slack. Its turned on for two days when a beast is killed to supply meat for the station. Neither SWER, or solar can pull a one ton beast down to frozen solid!!.
As to Lister diesel generators, most run slow in reference to 50 Hz, so fridge compressors are often replaced for no other reason than the motor flux is so high the motors melts down.
My observation to the cocky( VERY acceptable name for a farmer in Australia) to
"rev it up" meets with a sneer, because it uses too much oil.
Joe

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Old 6th Sep 2019, 1:57 pm   #24
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

Interesting Antipodean observations... I really wonder; were the power-companies' reasons _really_ justified, when you consider that almost every valve TV/radio in the UK from WWII to the mid-1970s (when solid-state and SMPS became the norm) used AC/DC and direct-on-line halfwave rectification - we didn't seem to experience our water-pipes dissolving en-masse as a result!

[AC/DC and half-wave mains rectification seemed to wortk OK in the US too - the classic "All American Five" broadcast-radios invariably used it. US TVs always seemed to use big mains-transformers though - I guess you can't get enough 'oomph' to do a decent line/frame deflection with only half-wave-rectified 117V as the power-source]
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Old 7th Sep 2019, 4:14 am   #25
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

Quote:
Originally Posted by G6Tanuki View Post
Interesting Antipodean observations... I really wonder; were the power-companies' reasons _really_ justified, when you consider that almost every valve TV/radio in the UK from WWII to the mid-1970s (when solid-state and SMPS became the norm) used AC/DC and direct-on-line halfwave rectification - we didn't seem to experience our water-pipes dissolving en-masse as a result!
That aspect was addressed in the Electronics Australia (EA) 1975 August article, as follows:

‘Two major questions arise from all this. The first: "Why is a practice, acceptable in Europe and elsewhere, unacceptable in Australia?"

‘One factor seems to be than with the common use overseas of non-polarised plugs and/or less rigid wiring conventions, transformerless receivers are more likely to be connected to the mains in random polarity, so that the DC effects may tend to cancel rather than to add. This, coupled with independent neutral wiring has, historically, diminished the apparent magnitude of the problem.

‘I gather, however, that some European supply authorities have been disturbed the Australian research into underground corrosion effects. It could lead to local research and a harder line in some countries.’


It was mentioned in the article that the concern was greater in the 1970s with colour TV receivers that it had been in the 1950s with monochrome TV receivers because by the 1970s there was much wide use of the MEN system.

My understanding (and it may well be wrong) is that historically, UK wiring practice favoured “independent” neutrals, wherein the neutral was earthed only at the substation and then sometimes via a resistance. PME was used for post-WWI installations and renewals, but it may have been some time (1970s or so?) before it became general. PME looks to have been an MEN derivative, but apparently not always, perhaps not often - with the bond between neutral and a local earth stake at the consumer premises. Whether the fact that neutral currents therefore had to travel some distance on the neutral itself before encountering an earth connection made a difference to how much thereafter returned by the earth route I don’t know.

The prevalence of overhead distribution in Australia (and New Zealand) was another difference factor. From the EA article:

“Some have argued that the DC effect of the suspect receivers was much less than the load current and that only a small portion of it travelled via the earth path. In fact, it would appear that the total DC load of such a receiver flows through the mains and, with overhead wiring in particular, most of it travels via the earth path rather than via the neutral conductor.”

In the UK, I think that much urban and suburban wiring was underground from early times, perhaps some original installations were underground. I don’t know what was the exact situation in Australia, but two of the locations we lived at in Sydney (Gore Creek and Lane Cove) during our decade there both had overhead supplies. (Three-phase as well, I think for the air-conditioning plant. At Gore Creek we were on a back lot, with an overhead line down the driveway – it got blown down once during a bad storm.) In NZ, overhead was the long-time norm except for the small areas in centres of some larger cities. As I recall underground did not become the norm for new subdivisions in the Auckland suburbs until around 1960.

The Australian electricity supply authorities were essentially guided by what the water utilities deemed to be acceptable in terms of potential differences. Again from the EA article:

“In Sydney, the Water Board has nominated a figure of 10 millivolts as the maximum potential difference they are prepared to tolerate between their pipes and the surrounding earth. Above this, electrolysis can make a significant difference to the service life of buried pipes. How does this figure relate to the possible effects of transformerless TV sets using half-wave rectifiers?”

“Seeking a positive answer, electricity supply authorities in Sydney made up thirty black boxes simulating the load of suspect TV receivers and installed them in customer's homes in various districts and in a likely distribution density. They then measured the potential of the service pipes in relation to ground, with rather disturbing results—a potential difference in some cases of up to 300mV, or thirty times the maximum figure set by the Water Board!

“If the current were to flow uniformly through and from metal structures, it would not be quite so bad but, in fact, it tends to find paths of lowest resistance and to concentrate along those paths. Under worst case conditions—say amps of direct current flowing from a large block of home units—the concentration could cause intolerable corrosion at specific points on underground pipes within a matter of months.

“In the magazine "The Contractor" published by the Sydney County Council, it is claimed that one ampere of direct current discharging from an underground metal structure can remove approximately 9kg of iron or 34kg of lead, in a year. Whose iron and whose lead is anybody's guess, because current flowing through underground pipes and structures is no respecter of premises! A's TV receiver may damage his own pipes, or B's or C's.”


Quote:
[AC/DC and half-wave mains rectification seemed to work OK in the US too - the classic "All American Five" broadcast-radios invariably used it. US TVs always seemed to use big mains-transformers though - I guess you can't get enough 'oomph' to do a decent line/frame deflection with only half-wave-rectified 117V as the power-source]
I think that there was quite widespread use of transformerless TV receivers in the USA, but not by all setmakers and I understand there were some who used it for a while and then reverted to the use of power transformers. Certainly in the mid-1950s whole series of TV valves suitable for series-string applications were developed, initially with 600 mA heaters and then with 450 mA and 300 mA heaters as well.

The USA as far as I know favoured multiple grounded neutral distribution, with much of it overhead, so might have had the same potential problems as in Australia and NZ. But during the era when transformerless equipment was commonplace, so were non-polarized plugs, so statistically at least the net DC on the neutral should have been much reduced. Also, the split-phase distribution system would have been beneficial in significantly reducing net DC on the neutral. Plus US distribution tended to use closely-spaced pole transformers. I think Australia was more like NZ, with larger transformers more widely spaced (maybe around a kilometre more-or-less in the suburbs), and so with longer earth pathways.

Returning to the Australian case, the opening paragraph of the EA article set the scene:

“There has been more heat than light in the recent discussion about the banning of certain transformerless colour television receivers. It has been interpreted as a defensive ploy by entrenched interests against further partitioning of the market. Others see it as a stick-in-the-mud attitude by Australian Electricity authorities, but neither suggestion squares with the facts.”

I’d say that the author the presented a fact-based analysis in support of his contention, and one which did consider overseas experiences. It would appear that the use of MEN system coupled with overhead distribution created a situation wherein the adverse effects of DC ground currents on “third-party” equipment (i.e. that of the water utilities) could not be ignored. (The MEN system itself had no major problem with the DC.)

Any rebuttal would, I think have to start with challenging the water utilities’ position on DC ground currents, and working up from there.


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Old 7th Sep 2019, 9:48 am   #26
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

The climate may be a factor. Much of Australia is very dry, or at least has prolonged dry periods. This will result in difficulties with earthing provision. This doesn't apply to the same extent in NZ, but they may have simply followed Australian practice.

Most UK domestic plugs were polarised by the 50s (either BS546 or BS1363) and while there would have been miswired plugs and sockets, there wouldn't have been enough to be significant. It's true that much of Europe used non polarised Europlugs for appliances though.

Overhead distribution was indeed very rare in the UK in urban areas, though you did (and still do) find it in rural villages.
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Old 7th Sep 2019, 10:22 am   #27
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

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This doesn't apply to the same extent in NZ, but they may have simply followed Australian practice.
The other way around, I think. NZ adopted MEN as a national standard in 1920, and Australia followed, using it not exclusively but to a steadily increasing extent. One reason for NZ’s adoption of MEN was poor ground conductivity in parts, less due to climate than to soil types, pumice being particularly bad. Somewhat south of here is pumice country, and for example its poor ground conductivity restricts the southern arc reach of the regional Bay of Plenty AM transmitter which is a few km southeast of here. Back in the 1950s we lived in the southern Waikato, and I recall that whilst reception of the more distant Auckland regional AM stations was fine , that of the closer Bay of Plenty station was subject to fading at times. Many years later I learned that it was mostly due to the poor ground path between here and there, even though in those days the subject transmitters were all 10 kW and used the then-standard NZBS 500 ft two-section antifading mast radiators. The earth pathway from Auckland was mostly over arable land, reaching pumice right at the end.


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Old 7th Sep 2019, 11:56 am   #28
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

Here in the UK in the 1960's house main earthing was usually via a water pipe or a copper stake in the ground the water pipe earth gave a good low impedance path but even a good earth stake could have resistance up into hundreds or even thousands of ohms this is partly why RCDs were introduced to mitigate the problem. In urban districts the earth was via the lead sheathing of the supply company's main These days DNO's often link the neutral and earth in an underground cable but never tell anyone so you end up with a sort of pseudo PME system but back in the 50's and 60's this was never done so here at least the amount of current flowing in the actual earth was small as most of it was on the cable sheath and of course non fault currents simply followed the neutral back to the supply transformer.
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Old 7th Sep 2019, 6:12 pm   #29
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

Interesting to learn that the concern was from the water rather than the electricity authorities in NZ. The numbers in terms of weight of metal compared with size of voltage are surprising! From what I understand in the UK the concern about 1/2 wave rectification was for the transformer rather than corrosion. Supply sockets were polarised by the 60s but the appliance cable generally wasn't, so chance still allowed correction.
At the time, there was still significant industry in residential areas - with heavy plant capable of deforming the mains waveform. Maybe this made the consideration of DC offset from a domestic TV less significant in comparison?
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Old 11th Sep 2019, 5:34 pm   #30
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Default Re: AC-DC Live Chassis Receivers in the Antipodes

There were probably quite a few reasons for Australia to avoid the AC/DC route.

Although there were a fair number DC Mains systems, the vast majority of customers lived in the major cities where AC systems were already the standard.

Valve manufacture ramped up enormously during WW2, with the vast majority of valves being 6 volt heater types.
After the War, there were large numbers of unsold valves held by the local valve companies.
At the same time, military surplus valves were available at "surplus stores", for "pennies" -------again, almost all 6 volt types.

It would have been an expensive exercise to tool up to produce series heater valves, for what was a smaller market, so such valves were normally imported, & hence were costly.

Radio manufacturers could obtain 6 volt valves, either relatively cheaply from the local valve companies or "dirt cheap" from disposals (from memory, only the smaller manufacturers used the latter option).

Power transformers weren't prohibitively expensive, & all the paraphernalia of isolating a "hot chassis" from customer contact was done away with in "one fell swoop"!

Apart from the large cities with AC Mains, & the smaller centres with DC supplies, there were a lot of small towns which weren't on any Power supply, & who relied upon battery radios.

These came in two flavours-
(1)Those using 1. 4 volt directly heated valves., either portables or larger "mantel" or "console" sets using what were called "Farm Packs" of large dry batteries.

(2)Those which had vibrator supplies run off 6 volt batteries---these all used 6 volt valves.

There was yet another group--- those who had 32 volt DC lighting plants.
Radios for this group were either Mains types, operated off "inverters", (either using large 50Hz vibrators, or occasionally, motor/alternator sets driven off the 32 volt system)," or "specials" made to operate with 32 volt HT, & utilising series heater valves.
The only ones I saw of this latter type were modified Ekco RM204s, which my employer made up on request.
This was in the early 1960s so they could use power transistors for the audio output.--- I'm not sure how this would have been achieved in the earlier period.

Receivers for the places with DC Mains were similarly made up in small quantities as "specials" or modified from standard sets.

TV only started in Australia in 1956, & followed the same pattern as with radios, using power transformers & full wave rectifiers.

By the time all the largish country centres had their own local TV site, DC Mains had pretty much gone the way of the Dodo, & without any real incentive to make transformerless TVs, they never happened (Apart from a little Admiral "portable")

Radio & TV servicemen hated the very idea of the things!

There was a bit of a fuss when Colour TV began, but the very early use of SMPS
offered chassis isolation in most designs, & it wasn't hard to modify those which didn't.
There was no reason to use half wave rectification with a SMPS.
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