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Old 6th March 2010, 09:16 PM   #1
newtube is offline newtube  United Kingdom
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Default LED power on light?

Hi guys, i built a simple se amp last year and i'm very happy with the whole thing. . .
However, i fitted a yellow led light into the front panel as a power on indicator but never got round to wiring it in, my question is how?

What do i wire the two leads to and is there a resistor needed etc?

Thanks.
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Old 6th March 2010, 11:24 PM   #2
rknize is offline rknize  United States
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All depends what you want to wire it to. If it is a typical yellow LED, figure 2.2V @ 20mA or so. You can wire it to a 6.3VAC heater wiring using a 220 ohm resistor. It will flicker at 60Hz. If that bothers you, you'll need a low voltage DC supply of some kind.
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Old 7th March 2010, 12:48 AM   #3
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If you can't tap from a DC point in the circuit and don't want the flicker use a full-wave bridge and a cap...(don't forget the led series resistor as well)... or, you could use a resistor and a dual color led (say red and green) wired in anti-parallel. It'll glow "yellow" on AC...

If you want to run off the line voltage (120VAC) use a 0.47uF, 200V cap in one leg of the AC line. Put a 1K resistor in the other AC leg. Use a 1N4004 (or such) diode wired in anti-parallel with the led. Put one leg of the AC on one side of the diode pair and the other AC leg on the other side of the diode. Still going to "flash" at 60 Hz (though you'll only see the flash if you wave your fingers in front of it or shake your head around while staring at it)...
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Old 12th December 2015, 06:03 PM   #4
peraho is offline peraho  United States
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Hi there-

I have a tubelab sse power indicator question, so I figured just add it to this old thread and keep it all together.

A friend and I are wrapping up our SSE builds, and he wanted to add a 6.3v pilot lamp from parts express as a power indicator, and I was going to do something similar with an LED.

Per Russ's advice above, for the 6.3v incandescent lamp my friend has, does that mean he just adds it into the two "T1-GRN" terminal blocks (one wire into each) on the board and that's it? I know this is a really simple question, but just wanted to double check before something explodes.

In my case, if I'm going the LED route, I use the same two terminals, but wire a 220 ohm resistor in series with the LED?

I just want to double check that with this sort of wiring, I'm using just terminal blocks, not connecting one end to the board and the other to ground or something. (This has been a great learning process, but still remember blowing up a multimeter back in high school...)

Thanks as always for the help!

Pete
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Old 12th December 2015, 06:46 PM   #5
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Originally Posted by peraho View Post
Per Russ's advice above, for the 6.3v incandescent lamp my friend has, does that mean he just adds it into the two "T1-GRN" terminal blocks (one wire into each) on the board and that's it? I know this is a really simple question, but just wanted to double check before something explodes.

In my case, if I'm going the LED route, I use the same two terminals, but wire a 220 ohm resistor in series with the LED?
Pete:
As far as I know, the answer to both your questions is :'Yes".
Wire the incandescent bulb across the heater supply, and do the same with an LED and a suitable dropping resistor.

A comment about some of the jewel-type indicator lights: I bought a bunch of new jewel light holders (imitations of the ones from the 50s & 60s) which use a #47 bulb- I can't rcall if I got them from PartsExpress or another supplier. The lamps in the new holders are shorter than the 'vintage' ones and it's almost impossible to remove the lamp ('push and turn') as it's buried in the holder. So my advice would be to check the lamp removal and insertion process before committing to a particular holder in an amp. BTW, I solved the problem with the jewel holder by replacing the lamp and lamp socket with a large LED and dropping resistor.
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Old 12th December 2015, 07:09 PM   #6
tomchr is offline tomchr  Canada
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When powering an LED from an AC source, beware that many LEDs cannot handle much reverse voltage. For example, my favourite red LED, the HLMP-D101, can only handle 5 V reverse voltage. A 6.3 V AC source imposes 8.9 V peak - a good 180 % of the rated absolute maximum.

To avoid excessive reverse voltage, use a diode such as 1N4148 or 1N400x in anti-parallel (i.e. anode of diode to cathode of LED) with the LED to limit the reverse voltage.

I usually run a standard red, green, or yellow LED at 5-10 mA. Going above that provides very little additional light. For low-current (high-efficiency) LEDs and blue LEDs, consult the data sheet for the LED.

Tom
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Last edited by tomchr; 12th December 2015 at 07:13 PM.
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Old 12th December 2015, 09:37 PM   #7
peraho is offline peraho  United States
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Thanks so much VictoriaGuy and Tom - exactly what I needed to know, and more...
Much appreciated.
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Old 12th December 2015, 10:00 PM   #8
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On my tube amps I always wire LED to B+.
This also gives indication that B+ is at a lethal voltage when you are working on it.
LED's require series resistor.
You can work out resistor by B+/0.01amps gives resistor value.
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Old 13th December 2015, 12:07 AM   #9
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Originally Posted by VictoriaGuy View Post
A comment about some of the jewel-type indicator lights: I bought a bunch of new jewel light holders (imitations of the ones from the 50s & 60s) which use a #47 bulb- I can't recall if I got them from PartsExpress or another supplier. The lamps in the new holders are shorter than the 'vintage' ones and it's almost impossible to remove the lamp ('push and turn') as it's buried in the holder.
Here's a pic with the jewel holder with the supplied lamp and a 'vintage' (long) lamp to compare with the 'modern' replacement. You need very sticky fingers (Spiderman??) to remove the short lamp from the holder.
BTW, beware: some lamps being sold as #47 (at inflated prices) are not the long type but the shorter replacement.
Fortunately I have a good supply of lamps salvaged from old radio hi-fi gear. It's surprising how many of them still work, once the dust and tobacco tar are cleaned from them.
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File Type: jpg old and new lamps jewel holder.jpg (98.7 KB, 66 views)
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Old 13th December 2015, 12:13 AM   #10
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Quote:
Originally Posted by nigelwright7557 View Post
On my tube amps I always wire LED to B+.
This also gives indication that B+ is at a lethal voltage when you are working on it.
LED's require series resistor.
You can work out resistor by B+/0.01amps gives resistor value.
Interesting idea- what watt rating do you usually use on that dropping resistor? (Seems like a hefty resistor is needed for that little job?)
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