Question - add LED power indicator to Aikido pre

[cjkpkg]

I put the Aikido in a new chassis and I am now using John Broskie's PS-3 PSU.

My question is how can I wire up a power indicator LED - my toggle switch has an LED buit into it. I have two others but those are in lower voltage applications so tapping for an LED was no problem.

I experimented with the heater circuit but it seemed to mess with the bias of B+/4...plus I'd rather not mess with the heaters as it is spot on running 12.6V.

The only other thing I can think is to rectify my incoming house voltage somehow.

Any ideas/guidance on component setup/values would be appreciated.

[cjkpkg]

I did find an online LED converter that let me put in 250V.

It spit out a resistor value of
1.24E+4
4.95W

dusting off the cobwebs I am thinking that a 12,000ohm resistor rated at 5W should work right? - at least according to the calculator

[rotaspec]

That's too much current for modern LEDs and therefore too hot for a 5W resistor. I would try 27k 5W resistor which should dissipate around 2.3 watts (still gonna run hot). That will be about 9mA through the LED which should be plenty of brightness.

[gingertube]

You should be able to run the LED from the DC regulated heater supply on the PS3 board.
I think from what you said above that you must have connected it incorrectly on your first try.
The negative of the DC heater supply is connected to a voltage divider (R8 and R9) off the High Voltage Supply such that the heater sits at an elevated DC voltage. You want to make sure that you connect the LED plus series resistor across the DC Heater supply (that is from heater +ve to heater -ve) and not from one side to ground. These board connections are labeled H+ and H-
A LED current of 2 to 5mA will be plenty. Using 2mA that means you would want a series resistor of (12.6-2.0)/0.002 = 5.3 K - Use 4K7. Power dissipated in the resistor will be about 1mW so any old 1/2 or 1/4 watt resistor will do.

The additional 2 to 3 mA drawn by the LED from the regulated heater supply will be insignificant and will not affect that supply in the least.

Hope this helps.

Cheers,
Ian

[HollowState]

For 120V line and a normal (medium) size red LED, a 12K to 15K 1 watt carbon resistor in series is all you need. No rectifier necessary. The LED doesn't need it. I've been doing this for years.

[Mooly]

You might notice "flicker" running an LED on 50/60 hz when viewed (out of the corner of the eye)

Modern LED's are bright on a couple of milliamps, and there's no way that will upset or remotely alter any heater supply.
I would just use a diode/resistor/cap to power the LED from the heater supply if the heaters are AC, and the same but without diode and cap if DC.

[Arnulf]

use a small capacitor and its reactance in paklce of a large resistor, it will reduce pwoer dissipation.

Read this: Marc's Technical Pages: Mains LED

Unlike what the schematic here suggests you don't need a full-wave bridge rectifier, one diode will do if you don't mind some small flicker.

[cjkpkg]

Awesome! thanks for the various tips. I will experiment and see which one is most elegant...

Gingertube...you're exactly right. I hooked the LED + to H+ and LED - to GND, not H-...I may try the H+ and H- hookup with a 12K resistor first. The PS-3 board is close to the switch so this would be the ideal option.

The other promising one would be tapping off the mains - Thanks Hollow!

[nigelwright7557]

Originally Posted by HollowState

For 120V line and a normal (medium) size red LED, a 12K to 15K 1 watt carbon resistor in series is all you need. No rectifier necessary. The LED doesn't need it. I've been doing this for years.

I have seen a few threads where LED's have failed without an inverse diode connected. For the sake of a 2p diode you might as well fit one.

[Arnulf]

OR, one could use one of those bidirectional LEDs (two LEDs in reverse parallel in same bulb). These are usually made in two colors (green and red) so together they give a nice organgish glow that fits well with tubes

This way maximum allowed reverse voltage per LED is never exceeded as both have Vg far below that value and protect one another from reverse conduction, overheating and consequent failure.