wouldn't a DC mains need to be around the same voltage as AC

The subject radios are rated 240 volts AC/DC.

BTW: Now that we have the benefit of the under-chassis photo, what you thought was a small transformer appears to be a choke.

It also needs to be remembered that, in that era, houses with electricity usually had it for lighting only. As appliances became available and affordable, they were plugged into light sockets via bayonet plugs -- polarity random.

I recall that just about every Victorian and Federation era house I've entered had three-gang mounting blocks in the kitchen with a switch, a three pin socket and a bayonet lampholder. The latter being for appliances with a bayonet adaptor instead of a three pin plugtop. Because I came along some 70-80 years after these homes were built I noticed that people would put pilot lamps in the sockets to stop curious fingers making their way into the lampholders.

One such residence was the Graythwaite mansion in North Sydney. It was fitted with its original gasolier piping and four generations of electrical fittings when it was acquired by the Shore School from the NSW Ministry of Health. Sadly I changed employers before getting the chance to see this property of significant heritage restored to its former glory but I did get a change to photograph some of the features of this place, which served as a private residence to wealthy gentry, including Sir Thomas Dibbs, brother of former NSW Premier, Sir George Dibbs; a convalescent home for returned servicemen and then purchase by the neighbouring private school for use as an administration building and museum. One day I'll dig the photos out.

A word now about rewireable fuses: The mention of the paper clip is pretty much the reason why state governments banned the installation of rewireable fuses. People were just doing silly things with them and most likely still do, in the millions of establishments still fitted with them. The older three core SDI VIR cables installed in the first electrified households was not as thick as the modern power-rated cable. It was closer to 2mm² than 2.5mm² and after connecting a radio, beehive heater and electric jug it would have pretty much consumed the available capacity of the single power circuit GTC had mentioned. During the day some or all of these would have had to be turned off before the maid ran the hoover over the rug in the drawing room.

Fires that have started over the last century due to overloaded power circuits would be too numerous to mention.

‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

I recall that just about every Victorian and Federation era house I've entered had three-gang mounting blocks in the kitchen with a switch, a three pin socket and a bayonet lampholder.

I may have mentioned on here before that during my high school days a mate's house had one of those in a cupboard containing a foldaway ironing board. I said in passing one day to his mother that I didn't like the look of the condition of that power point arrangement.

One morning in class I asked that mate, whom I shared a desk with, if he could smell smoke. He said, "It's me. My clothes. Our house caught fire last night while we were out. It started in the ironing cupboard." The place had to be bulldozed.

Excuse my lack of knowledge, but is 240v AC actually +240v and - 249v 50 cycles /second or is it the sum of +120v and -120v, making up the 240v measured? Just curious...

Also, what is a "Choke", what exactly does it do? I thought it might be a transformer as I discovered 435 volts at several places such as certain valve pins, wondering how 435 volts can be stretched out of the 240volt supply? I'm interested to know, as the more fascinated I become with these amazing things?
Yes I have seen bayonet light fitting on walls in very old houses and wondered why the hell anybody put a light in such a place??? Ha ha well that answers that!

It's 240 volts RMS. This page explains the difference between RMS and peak: http://www.electronics-tutorials.ws/accircuits/rms-voltage.html

Excuse my lack of knowledge, but is 240v AC actually +240v and - 24[0]v . 50 cycles /second or is it the sum of +120v and -120v, making up the 240v measured? Just curious...

Currently, most of the nation's electrical supplies are connected via the MEN (Multiple Earthed Neutral) configuration. This ties the neutral side of the supply to earth which means there is a potential difference of 240 volts between the active and neutral but also active and earth. If you remove that earth bonding from the neutral wire (not an easy thing to do because there are literally millions of these bonds in the electrical supply) then there will be a potential difference of 240 volts across the active and neutral and 0 volts between active and earth. But because of this, the protection provided by the earth conductor is no longer present. Because the wiring system is a three phase one, there is never a case of 120 volts plus 120 volts to equal 240 volts. Many electronic inverters do work in the way you describe but this is to simplify the design of the circuit that generates the power.

Also, what is a "Choke", what exactly does it do?

Usually they limit current flow to protect a circuit from overload. In some cases the voltage rises on an inversely proportional basis and this is how fluorescent lights work. The lamps need a strike voltage of more than 1,000 volts and once the lamp is lit the voltage drops to whatever the operating voltage for the particular lamp is.

‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

what is a "Choke", what exactly does it do

A choke is a filter. http://www.aikenamps.com/index.php/chokes-explained

Thank you very much for that, got my head around it finally! Good info, thanks

QUOTE: Good move that, they last a lot longer than a fuse

In the USA, we had Edison fuses, using screw in sockets, like our light bulbs. And one could insert an American 1 cent coin (copper penny) and screw in the blown fuse over it. This would get the lights back on, but you don't have overcurrent protection anymore. Oh, the fuseholder and penny combination would blow open at around 1000 amps.

More fun: the 15A, 20A, 30A fuses were physically the same size, and people sometimes replaced a 15A fuse with a 30A fuse as "They don't burn out as often as the 15A ones do"... As if they're light bulbs.

First time I saw a screw in fuse I thought it was a special kind of light bulb, and was going to try it in a table lamp. But my father stopped me, saying it was NOT a light bulb...

QUOTE: there is never a case of 120 volts plus 120 volts to equal 240 volts.

The power company always grounds the secondary of transformers. Otherwise capacitance from the primary (some thousands of volts) will create some high voltage (depending on the transformer's construction) that would have enough current ability to kill someone. Also protects against primary to secondary shorts, or if a high voltage wire should fall on a house feed service wire.

In the USA, the secondaries provide 240V end to end, and have centertaps, which are grounded. So we do get "120 volts plus 120 volts to equal 240 volts".

There were a myriad of power stations around in the early days before standardisation. Daylesford Vic was one of many with 240V DC in 1938. That necessitated no transformer.

240V RMS is not the same as 240V DC. Which is why the Barretter (Ballast tube) RMS (Root Mean Square) is a derived value based on Thermodynamics. It is the point on the sine wave that gives the same heating as DC.

So 240 RMS & 240 DC should yield the same joules, when heating. When rectified you get the peak of the AC wave form which is higher than the DC value. The barretter then heats to hold the current constant.

I would wonder at that being a transformer, unless its use when the set is running AC. I an suspecting a choke.

Marc

We are no closer to identifying this radio.

But I can tell you this:

Saxon branded coils, capacitors, etc., are a product of Eclipse Radio. Though I doubt if this a Eclipse chassis as it almost looks as if it is home made.

The dial assembly & escutcheon is a EFCO type "Moderne". See this thread:

https://vintage-radio.com.au/default.asp?f=2&th=586#5554

The ARTS&P label indicates 1934 with 4 valves. However there could be some inconsistency with the valve count. Some say that the valve count doesn't include the rectifier.

1934 model AC/DC radio's did not use barrettas. Barrettas started to appear in AC/DC sets a few years later. The barretta in this set appears to be an afterthought. This particular barretta looks like a type 302. See attacjed PDF file:-

Osram 301, 302, 303 and 304 Barrettas

My conclusion is that this set is either a homebrew or something from a very small manufacturer. Also the chassis looks like it was originally an early AC/DC set with no barretta or a battery set that has been converted to run on AC or DC

Furthermore, this set is extremely dangerous as it is and should only be worked on by someone with a lot of experience.

I noticed a original paper capacitor still in situ. Why has this not been changed.

this set is extremely dangerous as it is and should only be worked on by someone with a lot of experience

Agree 100%.

Jamie: would you kindly provide a sharp, close-up photo of one of those Saxon stickers, please.

I'm not sure which is the paper capacitor Carl, but I should be able to find it easy enough, I guess as a believer in "If it ain't broke, don't fix it" I have really only cleaned the set and fixed the valve top cap which was broken, as apart from that it works wonderfully well with great sound and appears in very good condition, having been stored for some 50-60 years, possibly more. When I bought it and took it home I noticed one of the valves sitting up, not pushed into it's socket properly, apart from that, nothing wrong with it, and as I have been told it is a dangerous one to work on, I'm avoiding actually working on it unless absolutely necessary, so long as it is working fine!
One thing though when I had it apart to take those photo's, I found inside the chassis, a very old and ragged Final Inspection card, not shedding any light on the manufacturer, however a date, barely readable 3/?/35 and a signature!
So I do not believe it is home made now, having a final inspection card, however the guy I bought it off, it belonged to his father, a collector in his nineties who no doubt acquired it in his youth. when it wasn't that old and had been superseded by more modern appliances (I'm guessing) and simply stored in very good condition. There is thus every likelihood that he may have altered it, but I can only speculate...There is a component inside, you can see, a square object with two wires coming out of it with a (although not visible in the photo) very colourful illustration/ sticker on it depicting a three headed "Hydra" type monster, unsure what this component actually is? But yes it is an enigmatic radio!