Kenwood KT-6550 Display lights Upgrade - NICE!
Today I had a few hours to replace the 3 blown Stanley 8V incandescent bulbs. These are normally wired in series. But I wanted to do something better than that. I rewired the circuit so that each LED is fed independently with 28VAC. So basically each LED circuit is in parallel with 28VAC power supply after the big 10 Ohm resistor. This is not necessary for an LED circuit but it would have been useful for the failure-prone 8V incandescent original bulbs. This way if one failed, the other two would stay lit. But it makes it easier to run the LEDs with different current if needed.
1) I used bright White LEDs from Radio Shack - two 5mm and one 10mm but you can really use whatever color you want
as long as they are not dim lights.
For the main display I used two high brightness 5mm white LEDs. Radio Shack P/N 276-0017.
For the meters I used one ultra high brightness white 10mm LED. Radio Shack P/N 276-0005.
People may tell you to use 10mm LEDs for this project. But the bright 5mm LEDs work well too. The 10mm may fit better in the rubber holders but it turns out the angle was wrong and I did not want to bend the metal. Using the two 5mm for the main display lighting allows play to angle them perfectly.
Also, don't use LEDs with diffused lenses. They throw the light all around. Use ones with clear-like lenses that focus the light. You want the light focused toward the acrylic light carrying material.
I reused the three rubber holders as these came in handy to keep the leads separated so they don't short out and to hold the LEDs. And a hot glue gun to secure the rubber holders in place.
2) Coming off of the transformer is around 28VAC for the front panel lights. A 10 Ohm resistor was in series with the original three, series connected incandescent bulbs.
3) I left the 10 Ohm resistor in the circuit, then connected two 1N4007 diodes in series with the resistor (yes, I am anal as one would do fine). Then I added three 2k,2W resistors. Each 2k resistor feeds each LED's anode (+). The 3 cathodes (-) I tied all together and connected to the other side of the 28VAC.
4) The result is a nice, well-lit display and gauges. This circuit will outlast all of the circuits of this tuner. One thing I noticed is the meters (which are using the 10mm LED) are a little bit dimmer than I would like but still nice. I think it is because the 10mm LED focuses the light two sharply on the concave "light pipe" of the meters. So maybe two 5mm LEDs there in series facing each side of the concave section would do the trick.
See the pictures. It really looks good.
I guaranty you that your tuner will sound better after making this modification. Okay I am just kidding with that part folks. Maybe it is just mental.
See pictures attached.