This board replaces the dial light bulb on the Dynaco PAS3 with a LED.
The kit ships with a clear LED and a 390 Ohm resistor to give off light similar to what the bulb did but uses way less power. The PAS3 transformer runs pretty close to its limit so taking a couple hundred ma load off makes a difference.
If you want to get fancy and have a different colour LED, use the following chart to choose the resistor required. You do not have to be exact, just do not go way lower as it will exceed the 20ma limit on most 5MM LEDs. The voltage after the diode and resistor is 9V if you want to do your own calculation with your LEDs particulars.
| COLOUR | V DROP | BRIGHT (20ma) | DIM (15ma) |
| RED | 1.8 | 360 | 480 |
| ORANGE | 2 | 350 | 466 |
| YELLOW | 2.1 | 345 | 460 |
| GREEN | 1.9 | 355 | 473 |
| BLUE | 2.4 | 330 | 440 |
| CLEAR | 3.2 | 290 | 386 |
| WHITE | 3.5 | 275 | 366 |
Solder in the diode, resistor, 10uF capacitor and LED as per the silkscreen. Note the orientation of the LED, diode and the negative side of the capacitor, Ensure you have these correct. The diode has a white line, the cap has a white line and the LED has a little flat edge.
If you want to control the brightness, omit the resistor and use a 500-ohm multi turn pot. Bend the legs on the pot 90 degrees so the pot lays flat on the board. Solder the pot in and before you install it, put your multimeter probes on TP1 and TP2 and set the resistance to what you see on the chart above for the colour of the LED you are using. Once installed you can adjust the pot to the brightness you prefer. Do not adjust it too low as you could burn out your LED.
To install the board in your PAS3, you need to remove the old light bulb holder. It is riveted in so you have to remove the faceplate then unscrew the front panel so you can lay it flat on the table. Unsolder the leads and use a drill bit a bit bigger than the diameter of the rivet and drill it out. It is pretty thin so it does not take much.
Clean up the leads and solder them to the “AC IN” holes on the PCB. Use the .75” 6-32 bolt and 3 nuts to attach the board to the front panel. Tighten up the first nut tight then thread on the second one so it’s about ¼” down. Put the board on the bolt and center the LED on the hole though the front panel and put on the 3rd nut..Test fit the faceplate and adjust the height of the LED with the two nuts so it does not hit the plastic jewel.
