Panel LED using heater tap

[chunkitup]

I need to get voltage for a red led to signal that the amp is on. I need 1.7v and I was thinking of using a half wave rectifier on the heater taps. Please correct any miscalculations: 6.3v - .7(diode drop)= 5.6 then divide by 3.14 = 1.78v
Would the half wave rect make the led flicker or strobe?

[Kazooman]

Curious why you don't just use a 6 or 110 volt pilot light? They are available in lots of styles and colors.

[Chuck H]

Half wave rectification is fine. IIRC from some experiments you won't see any strobing. Use high value resistors in the voltage divider. Like 100k/33k at 1/4W or 1/2W.

You could do the same thing off the fuse holder at mains voltage. With different value resistors of course (like a 470k/6.8k). That might be easier. I hate wiring filaments. Any extra leads to be soldered tandem only make it worse.

[chunkitup]

I think I will link off the fuse. Good call.

[Gingertube]

Just put a series string of 1K resistor, power diode (1N4007 or similar), LED straight across the AC heater winding. Power diode and LED need to be oriented the same way, e.g. power diode cathode to LED anode. If it is too bright then increase the 1K.

The power diode is there to handle the reverse voltage on the half cycle that the string does not conduct. LEDs have a reverse voltage rating of only about 5 or 6 volts so it is not a good idea to just string the LED and the resistor across a heater winding, always add that series power diode for safety.

Cheers,
Ian

[Chuck H]

He mentioned earlier that he intends to use half wave rectification.

[kleuck]

If you are using a virtual ground, just put the led across one of the resistors like that :

[kleuck]

Took the idea from the Pipsqueak : Pipsqueak pentode DIY guitar amp

[Jazz P Bass]

What a cool amp!
And it was stuffed in an ATX power supply enclosure.

[kleuck]

Mine too :

[Jazz P Bass]

Cool 2.

[Zozobra]

If you are using a virtual ground, just put the led across one of the resistors like that :
[ATTACH=CONFIG]21964[/ATTACH]

Thats a neat little trick. Appears to work with elevated heaters too!

[Steve Conner]

The LED will light up, but it'll also unbalance the virtual ground, increasing the level of hum. That may or may not be a problem in practice.

[kleuck]

It's not, at least with elevated heaters.

[I'm a beginner!]

Could you not use two LEDs, one with each resistor? Would that be less likely to massively unbalance the ground, and still be cheap?