Panel LED using heater tap

[kleuck]

You can yes, or use two standard diodes in series (1n4001 or the like)

[Chuck H]

There's also the issue of the OP needing 1.7V to illuminate his diode. Doesn't running the LED at 3.15V pose any problems?

[kleuck]

It doesn't work like this, the direct voltage drop is always the same, you just have to feed the led with more voltage than the direct drop, and limit the current to no more than the led can stand.
I a HR blue led, and it burnt -the 100 Ohms resistor is too low for them- but standard red or orange leds are fine with these values.

[J M Fahey]

Why are you making such a *simple* task so *complex*?
Just feed the Red LED from the 3.15V heater tap with 470 ohms to 100 ohms in series.
Period.

[kleuck]

Because it's even simpler ?

[Steve Conner]

Personally I prefer the Gingertube method.

[chunkitup]

I ended up going with a 820 and a diode in series with the led and it works perfectly. Thanks again

[Mick Bailey]

Why are you making such a *simple* task so *complex*?
Just feed the Red LED from the 3.15V heater tap with 470 ohms to 100 ohms in series.
Period.

That's all I ever do.

[stormbringer]

I've done it the Fahey way in the past, but I have been bothered by flicker.

Regarding Gingertube's method: is it possible to install a 10-47uF cap across the heater wires, after the diode to smooth out the voltage fluctuations and reduce flicker?

[Enzo]

Put the cap across the LED.

[R.G.]

Actually, a simple thing to do is to use six-pin-DIP bridge rectifier across the whole heater winding, with the heater voltage on the AC pins. The DC pins get the resistor and LED in series. Get it running, then pour epoxy over it and pot it up solid.
One of these:

costs $0.39 and isn't all that much larger than the resistor or LED.

[stormbringer]

Can the panel LED be powered by the 6.3V heater wires in an amp that elevates the heaters to 80Vdc?

[The Dude]

In theory, yes. The LED won't know the difference. It will only see the voltage across its leads. You'd of course need a resistor in series. It is a bit dangerous for the next tech who is maybe working on a panel LED problem. At the very least, I would sleeve the leads to avoid someone accidentally touching them.

[J M Fahey]

Yes, but the LED must float, no part of this circuit should touch ground.

[frus]

OMG just realized I did just that (raise the heaters), without even considering the LED
lucky I heat shrinked the led all the way, including the limiting resistor