Re: New BBC soap: Bert Coules?

Not only cheaper, but a _lot_ safer. A capacitor able to smooth EHT between cycles of the 50 Hz mains (or rectified versions thereof) stored a _lot_ of energy; one able to smooth a rectified 10 kHx signal stored a lot less. I'm not sure when the idea came in, but certainly by the time I got anywhere near sets, the capacitor was actually the tube itself: the inside and outside surfaces of the flare of the tube were coated with conductive material, which also meant connecting it to the final electrode was easier.

The energy more or less came for free: unlike oscilloscopes, most TVs didn't use electrostatic deflection (which only gave narrow deflection angles - very early sets had _very_ long tubes, often mounted vertically and viewer through a mirror!), but electromagnetic, using deflection coils. Coils by definition are inductors, and to make them change quickly - to make the beam fly back rapidly between lines - took a fair wallop of energy; recovering that with an extra winding to give the EHT seemed a good idea.

An early version of the switched-mode power supply. I think _some_ sets derived _all_, or at least some, of their other voltages from the line-output transformer (LOPT), not just the EHT.

The former - there _was_ no national grid. Lots of individual power companies.

I'm not sure about voltage, but of course definitely frequency. Before the grid, different companies didn't necessarily use the same frequency. Eventually, Europe settled on 50 Hz and America on 60. (Though I am pretty certain Britain never connected to the continent with AC, so we _could_ have gone our own way; the cross-channel interconnects are DC, with converter stations near Folkestone - Hawkinge, I think.)

Though economies of scale was probably the driving force for voltage harmonisation - light-bulb manufacturers, for example, wanted to mass-produce for one voltage; ditto switchgear and transformer manufacturers, so 11, 33, 66 (uncommon), 132, and 400 kV became the standard distribution voltages. (We don't go higher here: parts of north America, with very long runs, use higher.)

(Where?)

The industrial version of that was sometimes known as the Reyrolle design/pattern, as they were made by Reyrolle, mainly based in Hebburn (south bank of the Tyne, next to Jarrow). Seemed a good idea, except when a fuse failure resulted in the shattering of the fuse, after which you had to dig the remains out of the socket, either risking life or needing to have a whole circuit isolated.

The same way mains fed ones did.

By using the line oscillator to feed a ferrite transformer

Those connectors were used for 'technical' supplies in BBC TV centre when it opened in the early 1960s. We knew them as "Walsall Guage". The fuses used to be sold in Selfridges making me suspect taht soem of tehn 'mansion blocks' nearby used them, too.

Still made, but now known as "easigo"?

Those are different surely, 13A rectangular pins each rotated 90 degrees?

Dorman and smith?

Ah, I hadn't realised that CRT TVs generated the EHT at line frequency rather than mains frequency.

Makes life a lot easier if you need to drive the TV from DC as well as AC: the PSU just has to be able to accept a DC input at a certain level (which will be lower than the *peak* voltage of AC of comparable RMS value), maybe switch a few diodes out of circuit that would be used for an AC supply, and then generate line frequency from the local oscillator as normal.

Probably more difficult for transistor circuits which require low voltages, as opposed to valves which can accept (and indeed, *need*) much higher voltages that are closer to the mains supply. Were there any TVs, radios, hi-fi etc which used transistors and which could run off 240 V DC (or thereabouts). Or did the change to universal AC mains happen before transistor appliances became widely available?

It always amuses me in films/TV dramas set in the past when a character turns on a radio and you hear the sound immediately, instead of having to wait for the valves to warm up to operating temperature. I know there were some devices which kept the valve heaters powered all the time, even when the HT was turned off, but those were the exception rather than the norm.

In message snipped-for-privacy@mid.individual.net>, Andy Burns snipped-for-privacy@andyburns.uk writes

That take me back nearly 70 years!

And always, amazingly, just in time to hear the sonorous tones of the Prime Minister announcing 'I am speaking to you from the cabinet room at

In reality, they'd all have missed it and we wouldn't have been at war at all.

Except that in Neville Chamberlain's poncy Mr Cholmondley-Warner accent, it's the "Kebinet Room" ;-)

Sorry, yes tose were the ones that replaced the originals when someone decided that fuses projecting our of the live socket weren't a good idea. I still have one in a junk box somewhere. Yes - D&S.

There was another rival 13A which the Hydro board used as large at tehbnode

In message <qi0slt$rnf$ snipped-for-privacy@dont-email.me, NY snipped-for-privacy@privacy.invalid writes: []

(Most of them - see recent post re 12V valves!)

The latter; I'd say transistorised home electronics came in in the '60s, by which time universal AC mains was well established. (With a few localised variations as discussed in this thread!)

High-voltage semiconductors did exist, but until recently only in rare and specialised applications - I'm not aware of any domestic, or even professional, audio (for example) gear that ran on rectified mains directly. Even now, when they are very widely present in domestic equipment, they tend to be only in the power supply.

And it comes on just when the relevant item is being announced/shown.

I suppose, to be fair, having to wait for warm up, while more realistic, would rather cramp the storyline.

I hadn't realised that there were fused versions of round-pin plugs. All the ones I've seen, both 5 A and 15 A (usually after they have been removed for a 13 A plug to be put in its place) have had identical solid brass pins for live and neutral.

Unfused plugs were (and maybe still are) used in situations where the fuse in a plug is inaccessible. When I used to do the lighting for stage plays at school, the lamps above the stage each plugged into a round-pin socket, with each fader on the lighting panel having its own wire fuse. I remember the "joys" of having a fuse blow during a performance, hastily replugging the patch board to drive that circuit from an unused fader, repairing the fuse and then switching back at an unobtrusive moment. With a fused plug, you'd need to wait to the interval to repair it - going onto the stage, amongst the actors, with a long stepladder and screwdriver, during a performance, is somewhat frowned upon ;-)

The other thing I remember was the huge 3-foot-square resistive dimmer, with a large wheel on it, for dimming the house lights. It made an ominous graunching sound as it was rotated (which meant the audience knew that the lights were about to be dimmed!) and then emitted a nasty smell of hot shellac as the remaining wire glowed cherry red. We were warned to dim the lights *quickly* and not to leave the dimmer for any longer than necessary on an intermediate setting.

That was the "proper" stage in the school hall, with ancient equipment. The school also had a modern lecture theatre with triac-controlled theatrical lamps, dimmable fluorescent tubes and tiered seating. It would have been perfect for school plays apart from one crucial omission: there was no proscenium arch and therefore no wings for the actors to wait in until their entrance; someone did suggest opening the fire doors at either side of the stage and using those as wings, but the girls from the High School didn't like the idea of having to go outside into the cold and rain and dark whenever they needed to make entrances and exits - hardly surprising. So all that fancy stage lighting was a bit of a white elephant and was never used. The dimmable fluorescent tubes were very cool, though ;-)

All sounds very familiar, with twisty knobs that locked individual circuit dimmers onto one of two rods, so they could be dimmed in unison by turning one or other large handwheels?

Our dimmers were linear, with sliders that moved up and down. You put all the lights that you wanted to dim in unison on adjacent dimmers and then used a wooden batten to move them all together. That's why it was a pain when a fuse blew (which happened somewhere in almost every performance) because the rogue circuit had to be switched onto a non-adjacent dimmer (hoping that one was available *) which had to be moved separately but still roughly in unison.

All hideously unsafe: it's hot on the gantry about 10 feet above the stage, so you're sweating, and you hope that no sweat drips through the channel where the dimmer knob ran onto the bare windings of the dimmer or that your pen (for marking off the cues so you kept your place) didn't drop into the gap. When a total instantaneous blackout was needed for dramatic effect, there was a master switch which cut the power to everything, and made a hell of a bang with many kW of lights being cut off by a switch that arced; you then had to very rapidly reset all the dimmers to zero ready to bring up specific lights on the next cue.

(*) The sixth-former who designed the lighting marked contingencies where possible: "if these lights fail, bring up these ones instead as a stopgap".

Strand Grandmaster

I think others in this thread might be referring to some of these

I remember noticing that the 2A version of the round-pin plugs seemed to survive in shop window lighting, for some reason. []

I remember coming across somewhere that had ordinary fluorescents, but just connected to an ordinary dimmer; needless to say, it didn't really work - as you varied the setting, just different tubes either struck or didn't, and they all seemed very unhappy. Do you know how your dimmable fluorescents worked?

I've noticed recently some (either CFL or LED, not sure - LED I think) "bulbs" marked as dimmable; anyone know how they work?

Not quite as 'frankenstein' looking as that

and why not. They are still available and ideal for this purpose.

They work in a few ways..

they don't usually use simple capacitor droppers but a more sophisticated PSU that can recognise that the normal sine wave is being chopped and hence lower the current going through the LEDs.

they are smart bulbs that can dim themselves by recognising on/off/on patterns to start and stop dimming.

they use a resistive dropper so the normal chopped off dimmer output only lights them for the bit of the cycle its above the operating voltage. The problem being that the operating voltage will need to be quite high or the resistor will get really hot. It would probably need about 60+ LEDs in series so it would only be at full brightness at the top of the sine wave and you may notice more flicker even with a full wave rectifier in there.