Replacing incandescent bulb with LED

Post Reply New Topic

It's a well-known fact that LEDs are more efficient, cheaper, and environmentally friendly than incandescent bulbs. They also last a lot longer.

One characteristic of incandescent bulbs that LEDs do not entirely duplicate is that an incandescent bulbs act as resistors; they have resistance whereas LEDs don't. This property of incandescents was sometimes used in circuits.

Which leads me to my question.

In my beloved vintage 1970s receiver (vintage hi-fi is always better than new... but that's a discussion for another time), an incandescent bulb is used to illuminate an indicator for FM stereo. But the same bulb functions as a resistor in the FM stereo circuit. Simply replacing the bulb with an LED would therefore fry the FM section of the receiver. Finding a replacement is also unlikely, as the receiver is 30 years old and the part is likely proprietary.

In short, how do I measure the resistance that an incandescent light bulb has, when it is burned out and its watt and voltage ratings are unknown? Is it even possible?

with a voltmeter?..
there's probably markets out there for 'discontinued' or 'obsolete' equipment. If you can get a schematic of the unit (you'd be surprised what you can find on the web..., there will probably be some sort of part number? depends on the schematic, I suppose.

The bulb might have a wattage stamped on it. from there you put a voltage tester in line and get the voltage. with these two numbers you can calculate the resistance of the bulb and have someone make a LED-resistor pair to spec.

This might help
http://www.paetzke.com/ti83programs/fin ... watts-law/

A reputable electronics repairman could fix things up for you. take it to a radio/television repair place.

I demand pics of that receiver!

My receiver is a beautiful, vintage 1978 Kenwood KR-4070 (link to an eBay auction selling one). The auction has some excellent pics. Mine, regretfully, does not have the gorgeous wood side panels seen on that example, and the lamp that lights the signal and tuning meters is burned out (hence my question.) I'm also afraid of the stereo light burning out.

(If you were wondering, my dad bought it new when he was 22 years old or so. It was left at my mom's house after my parents split up, so it's sort of mine now (I live with my mom.) I love that receiver, and vintage hi-fi in general. The newest piece in my rack is a CD player from 1986.)

How big is the bulb? Is it flashlight bulb size or smaller like the grain-of-wheat size? If it's grain-of-wheat, an electronics supply store may have what you need. Or you may find a website for bulbs that has a picture of your bulb.

Two web sites for bulbs:

bulbs.com

1000bulbs.com