TR7 - VFO dial light
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My mail reason for removing the DR7 was to get to the dial lamp. I had suspected it was still incandescent, as it was dimmer than I would have liked. To my surprise, someone had rather sloppily replaced the lamp with a string of LED's and a series resistor. They had gobbed heat glue to hold them in place. See attached photos.
I replace with three LED's cut from a strip in a waterproof outer casing, double-sided taped behind the dial. These are bright white and the dial looks great. I installed a terminal strip on the side panel withh a flush screw to connect the LED and wiring that had previously been connected to the removed bayonet socket. Being in the outer sleave it would be very easy to replace them in the unlikely event that they ever failed in the future. Either it was not connected or I inadvertently pulled it off because it was tangles in the heat glue, the braided wire to the spring-loaded bar. I assume this should be resoldered there? Photos show detail of the change. The S meter and dial light are so bright they wash out in the front panel photo but look great to the eye. The bright white really bring out the blue color. The yellow light from an incandescent or the dim LED's gave an off color blue. -- Doug, WA3DSP |
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The way that a white LED works is that the semiconductor junction emits
light in the ultra violet end of the spectrum and a phosphor coating over
it converts the UV into visible light much like a florescent light bulb.
The UV still comes through and yellows the waterproof coating. A year ago
I replaced the LED strips in 2 Astron 50 Amp switching power supplies.
The LED strips have the voltage reduced to around 9 volts to cut the
brightness. One of the supplies is left on 24/7 as it powers my main TR7A
that I never turn off. The other power supply hasn't been used since
installing the LEDs. A few months ago I turned on the other power supply
and the LEDs were many times brighter and more white. I removed the strip
that been on all of the time and the clear coating was a dark yellow and
the LEDs had dark spots from the coating becoming brittle and holding in
heat. There is no heat in the power supplies and after the LEDs have been
on fo over an hour their temperature after removing the coating was under
80 degrees F. I talked to SuperBrightLEDs.com and they explained what was
happening and the sold me a strip that was not coated and it's been on
for a month and is still OK.
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73, Joe Pyles KC9LAD At 11:17 AM 3/7/2023, you wrote: I never heard of UV from LEDs that weren't specifically the expensive UV emitting type. |
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I found the old LED strip that yellowed after a year and here it is
compared to a new one.
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73, Joe Pyles KC9LAD At 11:17 AM 3/7/2023, you wrote: I never heard of UV from LEDs that weren't specifically the expensive UV emitting type. |
Doug Crompton WA3DSP
Gary WB6OGD