I have mentioned before that I have been using a 12.6V center-tapped filament transformer for accessory power, and that I was planning to use some of my supply of 2.5V miniature Christmas lamps for panel indicator lights. I expected to have to put additional lamps in series to bring the voltage from the center tap to each end into line with the lamp capacities. I use the full 12.6VAC to power twin-coil switch machines - with a 3-amp capacity it has no need for a CD circuit boost and I use non-stick power contacts (AKA studs and probe.)
Well, I installed some lamps - and ran into a problem. Seems that they could take power all the way across the 12.6VAC winding, even with the 6.3VAC center tap not only dead but disconnected. Fortunately the circuit had a total of six lamps in series (four serving only as resistors) so nothing died…
After some consideration, I added a pair of opposed diodes between the transformer coil terminals and the lighting circuits. Viola, no more unintended cross-power. And - no more need for multi-bulb strings for voltage matching. Most of the circuits are designed for two indicators in series. Now, with the 1/2 wave DC showing only 3V between the center tap and either end terminal, two lamps will light adequately, but three produce only a feeble glow. Suddenly the need for thirty-odd lamps pretending to be resistors went away.
Actually, the reduction isn’t all that big a deal. I have literally thousands of those miniature lamps, purchased for a couple of cents each (sockets included) during an after-Christmas clearance sale several years ago. What IS a good deal is that I no longer need to hide strings of ‘resistor’ lamps turning on and off for at odd times for no obvious-to-the-obsrever reason.
(That one filament transformer is only intended to power a single zone w