Ive just been given another AC/DC Mains set, A 1937 Skyscraper, manufactured by Radio Ltd (AK).
I wonder how "Radio Ltd" got away with it, Mains directly rectified with huge Wirewound resistors on the rear of the chassis and no rear cover , to top it off, of course only 2 core mains cable, because the chassis was in theory tied to Neutral", but if someone rewired the mains plug incorrectly, potentially the chassis could have 230V Phase on it.
Interesting because many of the early houses had few plugs so it is likely that the radio could have been connected to a light fitting. So... a 50/50 chance of livening the chassis WRT ground. All the American radios without power transformers, and indeed all the early NZ B & W tvs which had no power transformers, all had fitted backs to prevent the chassis being touched.
There was also a range of small mantle radios in the 1950s, mainly Philips, that didn't have power transformers, but these all had backs. Perhaps in the 1930s they didn't think it through? I am not sure when NZ adopted the multiple earthed neutral power system. Perhaps it was after this radio was manufactured so it would have been safe(r)?
That's one of the earliest NZ made AC/DC sets I've seen. All other AC/DC sets I have come across have had backs on them, even ones that were clearly conversions by radio servicemen. I strongly suspect this radio originally had some kind of back on it due to what look like vent holes in the side? The main market for these sets would have been places with DC mains I imagine.
History perhaps: Auckland's electricity was initially used for street lighting and electric trams. The Auckland City Council opened a rubbish-burning generation plant at Freeman's Bay in 1908 and a more efficient coal-burning station at King's Wharf in 1913. I believe these were DC - for the trams. All Auckland's power was generated within the city. By 1909, the council had signed up 195 electricity customers. Five years later, there were 2123. On April 1, 1922, the new AEPB (Auckland Electric Power Board) took over the council's power assets. It started off with 8000 customers and revenue of 210,000 NZ pounds. And then came radio! Chrs, DC
Likewise in Christchurch. DC power was supplied from a rubbish destructor which provided steam to generate electricity for the trams, starting in 1905. The network extended around the business district where it was used mainly for lifts but there were DC motors driving the organ blowers at St Luke's to the north and St Andrew's to the south. As far as I can ascertain these were the extremities of the system. AC power came to ChCh in 1918 when Lake Coleridge started supply. There was also DC in Akaroa from 1911 installed specifically for street lighting. It was changed to AC in 1923. Have a look here. akaroagenerator.org.nz/ The ChCh system will have had one side of the supply grounded because of the trams but the Akaroa system started life as a +/-110V system with the centre earthed. By 1937 the supply would definitely have been AC. All interesting stuff.
My first job was with the BBC as a transmitter engineer. I was posted to the stations at Burghead, and then Westerglen, both in Scotland. In the 1930s these stations were supplied with 230 VDC power, and in the 1970s the enormous copper busbars were still up on the walls. A fortune in copper! No doubt long since disappeared.