I'm replacing the tuner pointer illuminator lamp on a Scott R75s. It's a rice-grain bulb run off of a 6 VAC line with a 33 ohm resistor. Not having a suitable replacement, I used a white led out of a penlight. It runs on 3 button cells, so about 4.5 volts. (I turned it down lathe-like in a drill chuck. Took less time than placing an order, let alone waiting for it to arrive.) Using http://ledcalculator.net, entering a suggested voltage drop of 3 v for a white LED. I got a suggested resistor of 150ohms. Does this sound right? I've also heard it's best to install a rectifying diode to extend life of the LED. Do I install this anode to cathode? E.g. as a series double diode setup both in same orientation?