VU meter lamp to LED conversion - help needed

[Soul One]

Hey guys,

I am contemplating converting my Tascam M-520 VU meter lamps to LEDs. The stock lamps are 8V 55mA fuse-type pilot lamps. I thought about doing something similar to this guy:



I would need help with calculating the correct resistor value.

The schematics are attached.

 

[user 130681]

As the supply is AC, you may not notice but the LEDs will flicker.
I would fit a 470R 1/2Watt resistor in series with a 1N400*, (the voltage rating doesn't matter, use one on hand), after removing the link shown.
Fit both LEDs around the same way with the cathodes connected as shown.

 

[sodderboy]

I am all for LED replacements for meter and power bulbs. I like his little jam using the resistor as a frame for the LED chips. I actually soldered 5 chip LED's together to make lamps for a friend's compressor. Resistor on the outside, epoxied to a tiewrap. THAT was nuts, but they are still working over 5 years later.
I would do exactly what he does, but make sure you use a 5K LINEAR pot starting at full resistance, and slowly lower the resistance to get the desired brightness. The result will certainly not draw 55 mA. I would lose the shrink tube as it will certainly get brown over time. Still, I like the build and would follow.
Luckily for 1176, CL 1B, Avalon, Summits, etc. there are slightly larger pre-made LED signage assemblies.
Mike
PS: I also arrived at the 470 ohm dropper resistor to use with most outboard retrofits, but in this case the value will be a little more and wattage less. No need for a diode because the LED's are that already.

 

[user 130681]

I am all for LED replacements for meter and power bulbs. I like his little jam using the resistor as a frame for the LED chips. I actually soldered 5 chip LED's together to make lamps for a friend's compressor. Resistor on the outside, epoxied to a tiewrap. THAT was nuts, but they are still working over 5 years later.
I would do exactly what he does, but make sure you use a 5K LINEAR pot starting at full resistance, and slowly lower the resistance to get the desired brightness. The result will certainly not draw 55 mA. I would lose the shrink tube as it will certainly get brown over time. Still, I like the build and would follow.
Luckily for 1176, CL 1B, Avalon, Summits, etc. there are slightly larger pre-made LED signage assemblies.
Mike
PS: I also arrived at the 470 ohm dropper resistor to use with most outboard retrofits, but in this case the value will be a little more and wattage less. No need for a diode because the LED's are that already.

Some LEDs use GaAs and they do not like reverse voltage, hence the 470R due to the extra voltage drop.

 

[Soul One]

Thanks for your suggestions, @Jon S and @sodderboy!

I have to admit that I am a bit worried about the flickering. Maybe I ditch the idea of converting the VU meters to LEDs...

 

[user 130681]

Thanks for your suggestions, @Jon S and @sodderboy!

I have to admit that I am a bit worried about the flickering. Maybe I ditch the idea of converting the VU meters to LEDs...

Place a 100uF 10v or higher capacitor across the two LEDs that are in series., that will stop any flicker but I dare say you will not even notic it without the 100u smoothing capacitor.
Not two capacitors, just the one between the DC feed, (after the resistor and diode) and the bottom of the last LED.

 

[ccaudle]

Some LEDs use GaAs and they do not like reverse voltage,

What about anti-parallel LEDs? That would clamp the reverse voltage, and by conducting in both directions the flicker frequency would double and become less noticeable.

 

[user 130681]

What about anti-parallel LEDs? That would clamp the reverse voltage, and by conducting in both directions the flicker frequency would double and become less noticeable.

Try it. Depending upon the type of LED, the reverse voltage may be OK.

 

[Errit]

How about LED fuse lamps? You only have thema to replace your lamps by the LED version. I found AC 6 Volt types on AliExpress. On Amazon I found 8 Volt versions that are used in hifi equipment.

 

[industrialarts]

What about anti-parallel LEDs?

I just did that in some meters on a DBX556. Worked great, was across the AC voltage for the unregulated DC. I would suggest you get diffused lens LEDs, I only had clear and you could see some "hot spots" but really worked well.

 

[fillur]

little

 

[gyraf]

Fillur: You're a bot, aren't you?

/Jakob E.