Guide to replacing Signal meter bulbs with LED's

[Buick Mackane]

A frequently asked question here at TM1 is how do i replace my signal meter bulb with an LED ? What kind of LED do i need and what size of resistor do i need ? Etc. Well this guide will hopefully answer those questions and anymore you might have regarding LED's.

Unlike normal bulbs LED's have a positive connection and a negative connection. And have to be connected the right way round. Otherwise they go POP!!. The correct way to connect an LED is shown in the photo below. (But don't go connecting it just yet)




Before you go connecting it you'll need a resistor. The value of the resistor you'll need depends on the supply voltage and the LED spec. But for a typical LED with a supply voltage of 13.8 volts you'll need a 560 ohm 1/4 watt resistor. If it looks too bright using a 560 ohm resistor then slightly increase the value of the resistor. Use the calculator below to calculate the exact resistor needed for your particular circumstances if they vary from the above.
http://ledcalculator.net/


Contrary to what you might have seen or read the resistor can be inserted in either the positive or negative lead. Where you decide to put it is up to you. BUT DON'T LEAVE IT OUT.

Now there is lots of types of LED's. The ones shown here are 5mm. You might find that 3mm is a better fit. They are often called super / ultra bright LED's. The ones needed for signal meters are known as diffused LED's. Meaning they spread the light evenly. A normal non diffused LED can also be used. But you'll need to diffuse it first using some sandpaper. This only takes a minute. When you've done that the LED will look like the one on the right in the pic below. Don't go mad with the sandpaper. A quick rub is all thats needed.




Pre-wired LED's are also available. They also include a resistor, So its just a matter of wiring them up. Thats about it. Have fun

[Tigersaw]

The wattage of the resistor will depend largely on the current drawn by the LED not the actual R value, as most LED's forward voltage is in the region of 2v, and assuming we are using a 13.8v nominal supply then as you say, 1/4 watt will suffice unless its a extra bright one.
Try this site http://ledcalc.com/ as well.
From experience white LED's look too 'kitchen', and softer whites are closer to the original lamp.

PS its a lamp -- a bulb is something you plant in the garden

[Mudslinger]

I have found that with some LED's 1/4 watt resistors get quite hot.

You could either use a higher rated resistor, or as I have done use two 1/4 watt ones in parallel. If you use two 1k Ohms you will have 500 ohms resistance which is close enough...

Also warm white LED's look a very similar colour temperature to a regular filament bulb. If you like that nostalgic glow.

[MrWeetabix]

This thread is now 'stickyfied' for easy reference for all future generations of CB Radio LED Bulb replacement-a-teers

[Tim]

Much prefer the standard filament bulb lamp in those rigs that had them fitted as original, I think the LED's are too garish. I see nothing wrong with the soft glow emitted from a filament bulb. Perhaps a poll should be taken as to which everyone prefers.

[ChrisMagpie]

I was watching this video, the other day:
https://www.youtube.com/watch?v=N6g4DAEzvY8
Nice video. Replicates the filament bulb look
Video forgets to mention the very important LED polarity that the OP here points out, though

[Tim]

So has anyone posted up a comment on the video telling everyone that LED's have a polarity?

[dt307]

Not sure if been said ...
If you sand the led bulb with 400 grade sandpaper they will change from clear to misty
A cheap and good way to defuse hot spots caused by the beam angle

[Admiral]

I use LEDs now pure and simply because I know that's it for changing them, lamps will blow again within a week to 20 years, the LEDs with the same usage will pretty much last forever.

[Buick Mackane]

I use LEDs now pure and simply because I know that's it for changing them, lamps will blow again within a week to 20 years, the LEDs with the same usage will pretty much last forever.

Yeah. But you cheat and use pre-wired ones

[Admiral]

I use LEDs now pure and simply because I know that's it for changing them, lamps will blow again within a week to 20 years, the LEDs with the same usage will pretty much last forever.

Yeah. But you cheat and use pre-wired ones

You are correct, but in my defence my eyes are pretty crap these days.

[Buick Mackane]

Just bought some of these on ebay, Ideal for signal meters, Although you'll need to diffuse them first with sandpaper.
http://www.ebay.co.uk/itm/281867334255

[Mudslinger]

You don't have to diffuse them, I have found it makes very little difference.

[Admiral]

The only issue I've found is that with older HF kit, whilst the dimmer made a big difference on the old lamp installation, with replacement LEDs the dimmer button is virtually useless as there is no noticeable change in brightness.

[Buick Mackane]

The only issue I've found is that with older HF kit, whilst the dimmer made a big difference on the old lamp installation, with replacement LEDs the dimmer button is virtually useless as there is no noticeable change in brightness.

Well you could muck about and switch in different values of resistors, But far as i'm concerned a dimmer function on a radio is pretty useless anyhow.