Do black and white TVs use less electricity than colour TVs?

[Welsh Anorak]

Hi
To go back to the original question, for many younger people it will seem strange that there was ever such a thing as a black-and-white television - after all it makes little sense nowadays when every recent LCD screen is capable of displaying a colour or monochrome picture with no difference in power consumption.
If we take the Seventies as a benchmark (which is where Tim's original leaflet comes from) we have a (say) 20" thin-neck 110 degree mono CRT requiring around 18kV of EHT, one video output stage and a fairly low current frame output with any LT supplies being fairly rudimentary.. A contemporary 22" colour set - solid state or hybrid - will need 25kV of EHT, three video stages, a thick neck 110-degree tube with increased scanning requirements and some convergence and raster correction circuitry, not to mention a stabilised LT supply for the low voltage circuits, plus a much better sound output stage. We need to remember that power economy was not that high up the designer's brief at that time, otherwise I suspect hybrid sets would have been phased out much sooner.
The PD500 shunt stabiliser was soon consigned to history after the dual-standard receivers (pace Philips) were superceded. After all, a good example of the dual standard GEC hybrid (with no shunt stabiliser) would perforn at least as well - if not better - than a Bush which did have a PD500.
Glyn

Soft X-Rays are more of a hazard than the hard ones, they go right through, the soft ones stop in the body and can cause damage. Dad was a radiographer he winced every time he saw one of those shoe shop x-ray machines and told me why. Never did get my foot into one.

[G6Tanuki]

The 1970s were at the point when it became possible to manufacture an all-semiconductor [except for the tube] TV - both colour and mono - at a competitive price.

I'd bet that for a given tube-size a 1970s Toshiba all-transistor colour TV - or a BRC2000 - would take less power than an equivalent-sized largely-valve mono TV of the sort that the likes of DER, Radio Rentals, Visionhire etc were still buying from the mainstream UK manufacturers to inflict on their customers.

[Hybrid tellies]

Earlier colour tv's that used the delta gun tube were rather power hungry with single standard hybrid sets useing about 300w. Transistorised colour sets such as the G8, BRC3000/3500 and the RBM A823 used less between 150-200w of power. The typical large screen hybrid black and white TV, from the same era, used between 150-170w of power. It's interesting to note that the RBM hybrid dual standard black and white TV used the same power as the all transistorised RBM A823 colour TV at 165w. The power requirements for colour tv's has come down considerably over the years due to more efficient in line colour tubes and the use of switch mode power supplies. The last generation large screen CRT colour sets all used less than 100w. A good example being my main TV which is a 1998 21" Nicam stereo Philips TV which has a power consumption of between 50-70w.
So yes as a rule of thumb black and white sets did use less than their coloured counterparts and if black and white tv's had continued to be built this still would have been the case but the gap would have narrowed.

[Welsh Anorak]

Hi
Of course when it came to portables those 12v colour sets in the early Eighties used lots of power compared to the equivalent black and white models. Think Ferguson TX series with 12V converter, the Nikkai Baby 10 and so on.
Large screen mono designs could have been far more efficient if necessary - even the solid state ones didn't put much effort into economy - look at the Thorn 1615 with its big dropper, the Rank A816 (help!) and the Philips 320. Most other manufacturers just stuck with the good old hybrids as there wasn't too much of a demand. Eventually Pye and Philips did come up with fairly economic mono designs, but by then there was scarcely any market for large screen monos.
Glyn

[Studio263]

Glyn is right, the first generation of large screen solid state mono sets in this country were needlessly inefficient, I've been wondering for some time now why that was. It could have been becasue the stuck with the same thick neck tubes as the last valve sets used, meaning that considerable scan power was required to operate them properly - far more than was needed for the "pencil neck" tubes that the Japanese had.

However, it seems that in the end it was just down to tightness on the part of the manufacturers. They were interested in economy, component economy, so made the sets as simply as they could. Take the RBM A816 and the BRC 1600 / 1615 (much the same thing apart from the frame output stage) for example. These both used nearly identical shunt regulator circuits, not for the EHT but for the whole set! The plan went a bit like this:

A transistor is placed across one of the low voltage line derrived supplies, 22V I think in both cases. This progressively loads the supply to acheive regulation, and assuming that all the windings are tightly coupled (as they usually are in a LOPT) the output voltages at the various other circuit points will also be stabilised, as will the peak voltage at the line output transistor's collector by virture of the shunt circuit's damping action. Every shunt regulator needs some "give" in its supply of course to drop the surplus voltage across, in the case of these two sets this comes in the from of big resistors in series with the HT feed to the line output transistor, which is derrived from the mains much as it is in a valve set. No wonder the backs get hot! I was unable to find the figure for the BRC 1600 but the power consumption for the RBM A816 is given as 138W, quite unacceptable for a design of this period and very probably worse than the equivalent valve set.

B&O's first solid state monochrome chassis, as seen in the little Beovision 600, isn't that much better. This draws 100W for a 17" picture (admittedly a very good 17" picture mind you...), again due to its odd power supply arrangement. This uses stacked power transistors as an "electronic mains dropper", the circuit being rigged to produce not a constant output voltage as one would expect but constant scan power, the feedback loop being closed by an auxilliary rectifier connected to the LOPT.

I'm not convinced that screen size and power consumption are particularly dependent on each other in the sets of this period. An example is the Thorn TX9, this was availalbe with every tube size between 14" and 22" but the chassis are all interchangeable. The only thing that is different is that some have a link in the frame scan coil plug that corrects the range of the height control, so there can't be much difference in the difficulty of operating a "portable" sized tube and a full-sized one.

From an efficiency point view the best large monochrome set of this period was probably the Philips 320, which at least had a switch mode power supply using a thyristor and a bridge rectifier. Since the 520/ 550 (G8) colour chassis also uses a thyristor and many of the other circuit blocks are much the same this would be a good point of reference to compare the power consumption of colour v. monochrome sets. I don't have the figures here but my guess would be that the 320 uses between 1/2 and 1/3 of the power of the 520 (G8), so the leaflet may be right after all.

All such things are achedemic though when the weather is as hot as it is down here, what is needed is a truly efficient set that generates hardly any waste heat at all. Enter the brilliant Sony TV9-90UB, which is so perfectly designed that it doesn't need a regulator at all. All they did was to match the output voltage of the power supply and its source impedance correctly to what the set requires. See, that wasn't hard was it?