Re: New BBC soap: Bert Coules?

Not quite. The vibrator was encased in sorbo rubber to keep it as quiet as possible but its function was to switch the battery polarity to produce a 12V (or 6V) square wave which was used to drive a step-up transformer to produce the HT,

They came in two flavours, asynchronous and synchronous.

The asynchronous type drove the transfomer but a valve rectifier was needed to produce the DC supply whereas the synchronous type has two sets of contacts, one to switch and reverse the LT supply and the other to do the same to the transformer output. Being synchronous with the input, it switched the AC volgage to produce DC, so no rectifier was needed!

One place I worked at in the 1970s invested in a small number of early desktop computers. They were proprietary in that the format that they wrote to floppy disc wasn't IBM compatible. From my point of view, they could run a decent spreadsheet package and import the results into a report writer.

The place where they were installed had a lot of electrical equipment that could potentially introduce interference into the mains, so the company invested in "filtered mains" for the computers. The filtered sockets and the hard wired mains leads for the computers had connectors that looked like a standard 13A except that the earth pin was round rather than rectangular, like this

In those days they were expensive pieces of equipment, and the special connectors were also meant to make them unattractive as items to steal. Unfortunately they also made it difficult to borrow to work at home at a weekend. I bought a 2-way 13A adaptor that I took apart and drilled a round hole in one socket where the earth pin went in and buckled the earth connector inside so that the round pin was a snug fit. When reassembled the non-standard plug went in OK and that adaptor went into a standard 13A socket in my house. Taking a computer home (with permission) saved me commuting into work for 4 weekends of a rush job.

Jim

Nearly all devices today run on SMPS - the mains is rectified and smoothed and chopped to provide HF AC to a ferrite transformer.

They rn on DC just as happily. I worked on one piece of kit that could handle 48VDC to 240VAC without reconfiguration.

I am not aware of any pre the days of high voltage transirtors

Yes. Mostly

Back in the day, I remember seeing someone running a BBC micro from a

Incidentally, the valve heaters were driven directly from the car battery - 12V in the UK and (usually) 6V in the US. This led to the effective standard heater voltage of 6.3V in nearly all (mains) valve devices. 6.3V to allow for the on-charge voltage of 7V. Presumably a lot of valves were imported from the US.

Yes I tend to forget that a bridge rectifier as the input to a SMPS can handle DC as well as AC.

That reminds me of a prize-winning SMPS that our team designed at university for a project. We needed to drop a significant voltage to go from the AC input that we were supplied with to the max DC that the switching transistor could handle. For some reason we couldn't use a transformer. Most people used dropping resistors which incurs a significant loss. One of our team had the brilliant idea of using a capacitor in series with the load as a dropping impedance, and this was damn-near lossless. Obviously the SMPS could only handle AC, and the capacitor was sized for 50 Hz, so it would have been less effective (less voltage drop) on, for example, an aircraft

SMPSs are brilliant for regulation: we could detect *very* little mains ripple, even with the final-stage RC bridge out of circuit, and the voltage remained rock steady up to a very large load current and for a very wide range of input voltages. The only thing we had to make damn sure of was that the switching oscillator would *never* fail, because if the switching transistor was left turned permanently on for anything more than a trivial load, it exploded: the warning signs were very characteristic - a sound of rustling leaves for about 5 seconds, followed by a loud crack... and then another dent in the ceiling ;-) Fortunately we'd been made to wear safety glasses in case this happened - and we weren't the only culprits by any means.

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

Battery radios usually had valves with directly heated cathodes (ie the bit that glowed was also the cathode). When you switch on, the cathodes 'light up' virtually instantaneously (like switching on a light bulb), and the radio comes on immediately.

Mains valve radios and TVs made extensive use of valves with indirectly heated cathodes. Here. the cathodes are wrapped around an electrically-insulated heater, and it takes some time for the heater to heat the cathodes sufficiently for the valves to start working.

To reduce the warm-up time for TV sets, someone had the bright idea of leaving the valve heaters half on when the set was switched off. This might have actually reduced the switch-on thermal stress on the heaters, but it might also have resulted in a certain degree of 'cathode poisoning' - a condition which can occur when a valve is operated with a hot cathode, but at the same time it is not passing any HT current. The 'good idea' was probably short-lived mainly because of the increasing use of transistors in most of (and even all of) the TV set circuit, apart from the CRT.

In message <qi1vr8$sjc$ snipped-for-privacy@dont-email.me, NY snipped-for-privacy@privacy.invalid writes: []

Still used for electric toothbrush chargers. They do not like quasi sine wave inveters, and the magic smoke tends to escape quite quickly.

The "instant on" feature also lead to some house fires as there usually wasn't any indication that the set was in standby, and people went on holiday leaving the set in that state.

Though the feature only lasted for a few years, it lead to a (mainly superstitious) habit of unplugging the set at night that lasted for decades.

When CRT sets went all transistor, they somehow managed to make a tube that warmed up in about five seconds - a Sony colour 18" job I bought in

Nowadays, with LCD TVs, you have to wait about 15 seconds for the TV to be fully usable, e.g. it'll come on all right, but it'll be reluctant to change channel or volume.

It takes that long for the computer to boot. Modern TV sets are just one piece computers with a crippled operating system. Many of them actually run a version of Linux.

I think that was Max's point: we've actually gone _backwards_ in respect of time-to-available. Whatever the actual _reason_. Most of the more tech-savvy of us haven't noticed, as we're used to having to wait for computers (in computers, smartphones, cars, washing machines, microwaves, ...) to boot.

In article <hgyoP7s8$ snipped-for-privacy@255soft.uk, J. P. Gilliver (John) snipped-for-privacy@255soft.uk scribeth thus

And when are they upgrading the local distribution system to cope with these types of loads??..

The cars might the local distribution system won't!..

In article <qi0slt$rnf$ snipped-for-privacy@dont-email.me, NY snipped-for-privacy@privacy.invalid scribeth thus

IIRC Very early , and I mean 1936 models used a mains driven EHT supply!..

They were used in some makes of TV as a "Wattless" dropper for the valve heater supplies!...

In article snipped-for-privacy@candehope.me.uk>, charles snipped-for-privacy@candehope.me.uk> scribeth thus

Yes so it did of the Thompson's lane power station!

AC IIRC ;)...

Nev was a brummie. He was putting that accent on.

Bill

It was certainly AC. In the ADC theatre there was a transformer to get the voltage up to 240 for the stage dimming system. This system managed to drop the voltage back to 200v - so we could swap kit with the Arts Theatre ;-)