From ChristianH Sent Fri, May 3rd 2019, 10:26
I wouldn't expect much in terms of an original data sheet, at least not online - that was 20 years before the internet took off.=20 And - LED usage wasn't as sophisticated as it is now. Gee, even other colors than red weren't that common.=20 Rule of thumb for red was 1.2V, 20mA, which meant 180R for 5V TTL operation. That was the same I did back then without thinking.=20 Oh, and flat side is negative, but that was about all you needed to know abut LEDs. BTW, I think forward voltage mainly is determined by physical properties of LED color and hasn't changed since then. Current is a different thing, 20mA would be considered much by now for indicating purposes (in contrast to illumination). Chris On Thu, 2 May 2019 20:11:18 -0700 Brian Willoughby <xxxxxx@xxxxxxxxxxxx.xxx> wrote: > If this were my Polymoog ( ;-) ), I would try to find the model number of= the original manufacturer=E2=80=99s LED and look for a data sheet. Hopeful= ly, that data sheet would list the exact color wavelength of those LEDs in = nanometers. I would personally want the =E2=80=9Csame=E2=80=9D color of red= , not just any old red. >=20 > Modern LEDs are available in various shades, usually with good documentat= ion on the exact color wavelength. Of course, the really cheap LEDs just sa= y =E2=80=9Cred=E2=80=9D but you can still afford LEDs with better quality c= ontrol. Some have just a single wavelength, while others have a wide range,= but can still be =E2=80=9Cbinned=E2=80=9D by measured wavelength in much n= arrower ranges. You could save a little money by buying the unmeasured LEDs= , but the savings isn=E2=80=99t worth the tradeoff at your quantity. Instea= d, I think it=E2=80=99s worth paying a little more to control the color. >=20 > Assuming you can find the original specifications (or perhaps measure the= m), then finding a modern match should be easy. Most modern data sheets hav= e graphs showing brightness versus color, and you can match the brightness = as well. >=20 > As Murray pointed out, you=E2=80=99ll have to change the resistors, too. = The 180 ohm resistor sets the current, based on the LED supply voltage and = the LED forward voltage drop. If the modern LED has the same voltage drop, = then you=E2=80=99ll surely have to change the resistor to get lower current.= There=E2=80=99s a random chance that you could find a modern LED with a hi= gher forward voltage (that isn=E2=80=99t too high for the existing LED volt= age) and this would lower the current without changing the resistor, but it= seems unlikely that it would work out precisely. >=20 > One option that you should consider is buying modern LEDs with the same c= urrent rather than lower current. The reason for doing this is that you wou= ldn=E2=80=99t need to change the resistors. Of course, forward voltage and = efficiency are factors. >=20 > One thing to note is that LED brightness can be measured in lumens or can= dles, so you might have to convert between the standards if you want to dia= l in the same brightness. Also look out for the dispersion pattern - a dire= ctional LED will only be bright directly in front, while a non-directional = LED will spread out the brightness across a wider angle. The difference bet= ween lumens and candles is related to dispersion in different ways. >=20 > I suppose that I=E2=80=99ve made this sound like an incredibly difficult = task, but it=E2=80=99s actually quite simple if you do the math. A good LED= data sheet will give all the information you need to calculate a match to = the Moog original and perhaps even save you from changing the resistors. >=20 > Good luck! >=20 > Brian >=20 >=20 > On May 2, 2019, at 1:51 PM, Dan Goldstein <xxxxxxxx@xxx.xxx> wrote: > > I=E2=80=99ve got a Polymoog I=E2=80=99m restoring, and I=E2=80=99d li= ke to replace the old, original LEDs with new, modern ones. The originals w= ere 5mm bulbs, =E2=80=9CSSL-22=E2=80=9D, each with a 180 ohm resistor hooke= d up to it. > > =20 > > I=E2=80=99d like to replace them with new, modern red LEDs of equiva= lent brightness and lower current use. There are so many different LED valu= es these days, and I=E2=80=99m not sure how to know what would be the ideal= replacement LED. Can anyone offer any advice on specs for replacement LEDs= for a Polymoog? > > =20 > > Thanks! > > Dan > >=20