> > Quite probably, but the modern mains-side switcher is more > > troublesome and a lot less pleasant to repair. I think I'll stick > > with the room-heater in my 11's :-) > > Well, you could use a switcher, paralleled to the mains with a heater.
One reason I want to keep the original supplies in my 11's is that they are a lot easier to keep going than a mains-side swticher. Yes, they are switchign regulators, but the chopper works at 30V or so, on the output side of a big iron-core mains transformer. So no lethal voltage around. Using a mains-side switcher in parallel with a heating element would seem to be the worst of both worlds. Actually, no. That honour goes to the PSU in a Zenith MDA monitor which as I said 'combines the efficiency of a linear with the reliability of a switcher'. The design (if you can call it that) of this PSU is to rectify the mains, feed it into a free-running chopper circuit, then a transformer. The output of that is half-wave (!) rectified giving about 18V DC. Note the chopper free-runs, so there is no regulation applied at this point. That 18V is then fed to a discrete-transistor linear regulator. And that's not the end of the 'curious' design. As you know, a linear regualtor compares the output voltage of the supply with a reference votlage. That reference voltage is typically produced by a zener diode. Not in this monitor. It uses the drop across the power-on LED. Which means it is important to use a green LED. Another colour, with a different Vf, and the PSU output is wrong. > Just as you can use a CFL along with a heater for some applications > that call for an incandescent. I once saw a curious lightbulb which contained both a mercury vapour discharge lamp and a filament. The idea was that the latter would provide some red light to go along with the predominantly blue/green mercury lamp. I think the filament was also the ballast for the dischage lamp. Oh well.. The time I need a filament lamp is when I am using it for the electrical characteristics (e.g. using it as a ballast resistor), so no kludge with a CFL is likely to work -tony
