UK LV Electricity Voltages 1954

[broadgage]

Indeed, back in the good old days, electricity was largely for lighting and the odd AC/DC radio and maybe a heater.

The red wire was live. Fuses and single pole switches that formed part of the fixed installation should always have been in the red wire, no matter if this be from the positive outer or the negative outer of a 3 wire DC system, or from any phase of an AC system.

Some authorities recommended that when the live wire was derived from the negative outer of a 3 wire system, that the wire should be red as required by regulations, but ALSO identified by blue marking.
I have seen this on old installations, where the red (live) wire had a blue rubber sleeve at the termination to a switch or outlet.

[Tim]

The correct colour code was
RED=POSITIVE OUTER
BLACK=CENTRE WIRE
BLUE= NEGATIVE OUTER

For a 2 wire circuit derived from a 3 wire DC system the correct colour code was black for neutral and red for live. This led to confusion at times since many people expected red to be positive, when in fact in a house connected to the negative outer, the red wire was negative.

I wonder if that's why some peoples mains connections are "reversed". My parents in law had a wooden fuse box(I kid you not) with fuses in the -ve line until the early 90's.

[hannahs radios]

Just a comment to G6Tanuki's post. Your ancient relative's TV would have had a big dropper resistor and I'm sure they would have set it on the 200 Volt tap and possibly bypassed the rectifier valve. So she would got a full picture despite the low mains input.

[SteveCG]

The discussion of 3 wire DC has been thought provoking.

I wonder how people with 2 wire AC/DC radios with 2 pin reversible plugs got on in a home that had the live line with (say) -200V?

What would happen if the set's supply got reversed? Clearly if the set used a dropper resistor then the heaters would still light. Also the set's valve rectifier should have stopped the -ve voltage being put across the set's smoothing electrolytics in a reversed manner. Otherwise on switch-on (perhaps, say, after moving the set to a different power outlet in the house - or connecting it again to the lighting outlet in the room) silence from the set followed by a bang ? (Especially if the rectifier has been bypassed as hannahs_radios's post no. 23 has suggested happened.)

[emeritus]

AFAIR, the mains voltage selector of out first TV, a Bush that dad had bought for the Coronation, had separate voltage setting positions for AC and DC, and that the DC range was only 230V to 250V.

[TonyDuell]

I think in some cases the short across the rectifier (valve or metal) was made by a cartridge fuse that was clipped in only for low (200V etc) DC mains. The idea being that if the mains is reversed and the smoothing capacitors break down then this fuse would blow before too much damage was done.

I also seem to remember (at least for some TVs) you set the heater dropper to the right value, set the HT dropper as low as it could be set, got the set working on the low DC mains as best you could (often the picture would be too small, etc)and then fitted said shorting fuse.

[broadgage]

In most cases a valve radio connected to DC mains of the wrong polarity would suffer no harm whatsoever.
Remember that connection was often to a lamp socket or a 2 pin socket outlet into which the plug could be inserted either way around.

The valve heaters would light, but the wrong polarity supply would be blocked by the rectifier valve and no harm would result.

Such sets were often designed for operation from AC or DC mains, and worked fine on AC despite the polarity being wrong half the time.

[Nickthedentist]

Coincidentally, I've just been reading the instructions for the Bush VHF90A radio (c.1958). They advise DC mains users to plug the set in, wait a minute, and if nothing happens, simply reverse the plug.

Same as the this one really: http://www.pasttimesradio.co.uk/scra...bush-vhf70.pdf

[emeritus]

Just checked with an early 1950's Bush TV leaflet, and the specified DC mains range was 220V to 250V. The AC range was 200 to 250V, 40 to 60 Hz.

[Station X]

Originally Posted by SteveCG

What would happen if the set's supply got reversed?

The instructions with AC/DC sets generally stated that if the set didn't work on DC, the mains plug should be reversed.

[broadgage]

Operation of valve equipment from both AC and DC mains was rather a compromise since no simple means existed of getting both the HT and the heaters at the correct voltage.

Consider the heaters first. A series heater chain may be worked from any mains voltage in excess of the total heater chain voltage. It is a simple matter to provide a dropper resistance with different tappings to suit different mains voltages.
This will work equally well on AC or DC mains, a simple series chain of resistors will work just the same on AC or DC.

Now consider the HT supply, this was commonly obtained by half wave rectification of the mains and smoothing with capacitors. A valve rectifier introduces a roughly constant voltage drop of say 30 volts.
With 200 volt DC mains, the HT would be about 170 volts.
Now connect the same set to 200 volt AC mains, the capacitors will now charge to a voltage approaching the peak of the AC mains, say about 270 volts, or 240 volts after deducting the rectifier drop.

There is no simple way around the problem that rectified and smoothed AC will produce a higher voltage than a DC supply of the same nominal voltage.
A choke input filter circuit helps a bit as compared to capacitor input.

A basic valve radio would have worked acceptably with an HT voltage that varied a lot, though the audio output might have been limited on DC mains especially if only 200 volts or so.

The more complex circuitry of TV sets were less tolerant of varying HT voltages.

[TonyDuell]

The problem that AC mains and DC mains of the same specified voltage (this being the RMS for the AC mains of course) give different HT voltages can be got round by having an extra dropping resistor in the HT circuit (normally on the mains side of the rectifier) on AC mains only.

I have never seen a radio which did this, but TVs often had different settings (either on the votlage selector panel or with wires you clipped onto the tags of the dropper resistor) for AC and DC mains of the same nominal voltage. It was these I was thinking of when I mentioned that some sets (I meant TV sets) shorted out the rectifier with a fuse on low DC mains. Point being that on 200V AC even with the drop across the rectifier you could get a high enough HT voltage, with 200V DC you couldn't.