This thread is an offshoot of the previous one which discussed the need for and viability of AC/DC receivers.

Enjoy.

One thing to remember with earthing valve radios is that whilst the earth connection provides the normal protection that earthing provides, because the secondary winding is connected to the chassis, the isolation protection provided by the transformer is removed.

This is because the neutral wire on the primary side of the transformer is connected to the earth wire on the chassis (and therefore the centre tap of the secondary winding) via the MEN link in your main switchboard.

Food for thought.

A lot of Australian sets through the fifties had no mains grounding. Some claimed the set to be sealed and you could not touch anything alive.

As far as I am aware, from the 1920s right up to the 1960s there was no earthing. Some last-minute models like the Kriesler 11-99 came with a three core cable and thus earthing (whereas the 11-90 and 11-81 did not) and the sealing that manufacturers referred to was the same as the Australian Standards referred to when judging the suitability of BP connectors for hard-wiring in buildings - the 'standard finger test' where if a normal human hand could not come into contact with live parts without the use of a tool then the item was deemed safe. If the shaft on a potentiometer went live it was still deemed safe providing the grubscrew on the knob couldn't be accessed. How times have changed.

If you guys point me in the direction of companies that sell (and deliver) stuff I will put their details in the Services Directory over the Christmas break.

It gives food for thought as to the real danger of AC/DC and transformerless sets when the voltages are around 240AC and DC will "Grab" you.

These sets were always regarded as trecherous as there was always a 50/50 chance that the chassis had Active on it.

One reason I have an isolation transformer.

I did have a CRO where the focus & intensity pots were metal shaft and on, and insulated from, the front panel.

These carried 5KV. I did actually point out the danger of that when one pot decided to track & flash over.

The manf.in question was quite arrogantly defensive about it. I believe they got sued when a student got zapped by one doing the same thing. And he would not have had to remove the knob to achieve it.

Always, when fixing / tampering with these things "Caveat Actor" applies.

Marc

Heh... I have one AC/DC set here, an Airzone Radiostar. Even though I am a licenced electrician I am leaving that one idle for the time being. My workshop isn't in a state for doing repair work in at the moment and the kitchen table isn't appropriate as there is too many interruptions around it like the telly, phone, computer, etc.

The other thing is that it requires some P-base valves and I don't have any aside from those in service in other sets. When all is said and done, it's not a priority.

Technically I am a chemist, albeit I seem to do a lot of everything other than that.

I have worked on a couple of them. That is why I have everything to endevour to aviod being bitten by one.

That Airzone sounds familiar with one waiting to come in. It uses a C1 on the heater string.

I did have a Philco that some one messed up and had a filament transformer fitted. plus other undesirable mods. that were it's downfall.

Transformer was handy, as I applied it correctly and then provided a 180V DC HT source. All of the PSU in a seperate box with appropriate polarised plug & lead.

Much tidier & safer.

Marc

One thing to remember with earthing valve radios is that whilst the earth connection provides the normal protection that earthing provides, because the secondary winding is connected to the chassis, the isolation protection provided by the transformer is removed.

Yes, by definition you can't be isolated from earth if a unit is earthed. However, I'm seeking the protection of an active to metal parts fault via the earth return, especially as I'm doubling the primary voltage.

As for transformerless radios, I got the mother of all shocks across my chest in the school physics lab in 6th Year (year 12) from one of those. Luckily I touched the chassis with the back of my right hand (my left hand was resting on the gas tap on the bench) and my right hand was repelled away from the chassis otherwise I would not be here typing this and my physics teacher would have been on the stand in the Coroner's Court trying to explain why he let his students loose on lethal equipment.

I let out an expletive and the teacher turned white when he realised what had happened. I felt curiously energised by the experience and I've never forgotten it, nor have I been zapped by mains voltage ever since. Once was definitely enough.

The big problem with DC, aside from what has been discussed is that when it throws a spark it will not quench by itself. Unless there is some interference that quenches the spark it'll just keep going until either the two 'electrodes' have burned away or a fire has started. This is why DC is unsuitable for the switches in our houses. They are physically too small to quench a DC spark, particularly when the supply has the capacity to feed a higher current than the radio would normally use.

DC is starting to fall back into use for HV transmission networks because it is more efficient to transmit, though it is very unlikely it'll be used on the domestic scene again and it's not such a bad thing. It's hard enough to make a 240VAC appliance safe for both smart and silly people without having to consider the extra requirements for DC operation.

It makes me wonder what sort of market share AC/DC receivers enjoyed and what suburban DC footprints existed. There would have to be a certain number of punters connected to a DC supply for these receivers to be viable to manufacture.

DC's great advantage in transmission is the interconnection of dissimilar AC grids and bypassing the considerable problem of synchronizing AC to AC.

In Oz, and probably in the USA too, transformer-less sets avoided the manufacturing cost and space of a transformer. I don't believe that any domestic DC supplies were a genuine commercial consideration for manufacturers in Oz, particularly 240v DC.

I read somewhere that in the USA those sets killed or shocked so many people that manufacturers were eventually forced to take the mains off the chassis and run it along an insulated bus in the pan.

One must not forget that in 1937 there was not much in the way of a grid & several towns ran from 200V to 250V AC and several Like Appolo Bay, Avoca, Broome DC & Broken hill was 115V AC at 100 Hz.

1937 Radio Trade Annual has four pages of who had what at that time.

Do note there is no "Corona" discharge loss with DC

The secondary being what it is in most domestic sets does keep the current pretty much below killing range and isolates from the full capabilties of the mains.

Line amps like the Philips I have, I would suggest in being able to put 320V on plates and run other items would have around half an amp capability on the secondary. If that could deliver half that or more, it is likeky to kill.

Marc

One must not forget that in 1937 there was not much in the way of a grid & several towns ran from 200V to 250V AC and several Like Appolo Bay, Avoca, Broome & Broken hill was 115V AC at 100 Hz.

Yeah, AC, but who in Oz (in commercially significant numbers) had 240v DC?

1937 Radio Trade Annual has four pages of who had what at that time.

I'd love to have that as a reference. Has anybody posted it online? (hint, hint)

Yeah, AC, but who in Oz (in commercially significant numbers) had 240v DC?


Many small settlements in the sticks ran 240Vdc up to the late fifties. In SA along the rail line between Broken Hill and Port Pirie there were isolated stations every 30 miles or so with up to 20 homes for station staff and fettlers.

As the only electric appliaces in these homes were a frig, radio, some small jugs and lighting, the load late at night was quite small. During the day, the generators were run to supply the needs of the residents and railways and to charge up a large battery bank. Around 9PM the generators would be shutdown and the batteries used to supply the needs till the next morning.

Some places like Cockburn on the SA/NSW border, Mannahill, Olary, Yunta, Mingary etc used this system.

At some larger settlements which had a hotel such as Yunta, the hotel had its own AC generator to power the essential cooling equipment of its products.

Some of the larger sheep stations also used this method instead of the usual 32V lighting systems.

More about BH's different systems to follow. Massive thunderstorm approaching.

Cheers, Graham...

There were parts of Sydney that had DC mains. Further to Marc's comments, most suburbs were served by smaller municipal power stations and there was pretty much no uniformity at all. You got what your local station offered or generated your own power, though of course for most people the latter wasn't a practical option.

The last DC substation in Sydney was turned off around 1989 though it did not service any domestic installations. This was in Clarence Street as far as I remember and it powered many of the lifts (remember the old lifts with trellis doors powered by compressed air?) and escalators in that part of the CBD until the advent of reliable controls for AC machines.

Search engines seem to be completely useless at the moment. I cannot find any reliable information on what was generated where apart from the biggest of the stations, such as White Bay, Ultimo and Pyrmont.

Brad, we have drifted off this thread's specific topic onto mains supply types in general, which is also of interest. Can you split the thread into two, please?

It's possible to do but has to be done manually. Let me see what I can do.

I think we can weed out the bits related to reticulated power .

We have wandered but this is discussion rather than technical, which we can perhaps move the other to?

We then re-lable this as an explanation as to why AC / DC & 32V radio's were made.

In a nutshell: There were 32V lighting plants running into the 60's & beyond. We did not get connected to the grid until 1962. At that point transistors were still to really develop.

Until every thing was standardised after WWII,it was chaos.

I have sent a listing of the 1937 situation to Brad (someone will be pleased) The first lot bounced so I have shrunk them a little more.

Pkzip is looking better by the second.

Marc