high flux LED in series with ck to ground?

[Dan T.]

Could I put a 1-3 watt Luxeon LED in series with the cathode resistor in a preamp stage and use that as an indicator? The vF would be around 3.4V .

[Don Moose]

Can you get a satisfactory brightness with the 2mA or so of Ik?

That Vf is consistent with an Rk of 1K7 or so, which doesn't seem out of line for a second stage.

[Don Moose]

Oh - and the LED would be REPLACING (most of) the Rk - if you wanted an Rk of 2K2, you'd put your LED and a 470R or 510R Rk.

[Dan T.]

oops , I meant Rk not ck .Thanks

[Dan T.]

2ma wouldn't be very bright ...well I'll just have to put some more thoughts into this.Maybe some experiments...
Thanks Don.

[Don Moose]

What is it you want to indicate, anyway?

[Enzo]

" If you can see this, then the room lights are off, when lit."

[Earl]

From peeking at the data sheets for these jobs, it looks like they run at about 100mA. I'm not sure that the Ib in a pre-amp tube would even get one to conduct .. ?

[Zoe_N_Iain]

Why do you want to use such a 'big' LED? There are plenty of types that will light pretty brightly with 1mA or so of cathode current. I use them all the time to bias preamp stages.

What sort of indicator are you intending it to be that it needs to be such a high power device?

[Dan T.]

I had a few of those LEDS floating around the junk box,and figured that you ususally see a 1/2 to 1watt resistor for the cathode in a preamp.They are rated for 350 ma for the 1 watters and around 750 to 1500 for the 3 watters(at 3.2-4Vf)It sounds like I could get away with using a 5mm one if all it has to dissapate is a ma or 2.
I was thinking that it would flicker a bit while playing and look kind of neat.Thans for the input ,I will check back when I try this,and let you know what happened.