Fender Super Twin.

[DrNomis_44]

I think I ended up using 2.4k for the blue LED in the buffer. I normally just put the LED in a breadboard and try resistor values until the brightness looks about right. This is only around 2 or 3mA running off 9v but the brightness looked good.

I've used a resistor value as high as 47k for a blue led running on a +15V DC supply, and it was still pretty bright,I did a quick calculation and found that a 3k3 resistor will limit the current to 1mA on a +4.8V DC supply for a Blue led, I used 1.5V for the forward-voltage of a Led in my calculation.


I used the following formula to calculate the resistor value:



R=Vs-Vf/I


R= Resistance.

Vs= Supply Voltage.

Vf= Forward-biased Voltage of the Led (typically about 1.5V for standard 3mm and 5mm Leds).

I= Led Forward-Biased Current.


Although, some 3mm and 5mm Blue leds have a Forward-Biased Voltage as high as 3V.