LED simulating a vacuum tube.

[Crontox102098]

This is just an idea... Could work?  

I draw as a toddler, i know.

[bluebunny]

Visually, yes, it should look great!  But your LEDs appear to be in parallel and each powered by 9V.  They will burn up.      So you still need some resistors, like you would with a regular indicator LED.  And from what I recall reading before (from R.G. or PRR, perhaps?), since you have different colours of LEDs, some may hog all the current, so only one may light.  (Did I get that right? Anyone?)  I don't recall the solution, but I think you may need individual resistors for each LED.  Otherwise, it's a cool idea!   

[bool]

Just take a look at some behringer stuff... for inspiraton.

Everything you need to know is there.

[merlinb]

I think you may need individual resistors for each LED.

Put the LEDs in series, with one resistor, and you're golden. (Not that real tubes glow that much!)

[composition4]

But what does it sound like?

[merlinb]

But what does it sound like?

Orange.

[samhay]

As Merlin said, put them in series.
I guess you could then use them to clip to ground if you had a big enough signal...

[Crontox102098]

Thanks a lot for your help... 

Cheers!

[WhiskeyMadeMeDoIt]

LED's can be powered in series as has been suggested.
To figure the resistor you have to use a little Ohm's law and some basic math.
Using your diagram we will attempt to figure out an appropriate size for your resistor.
First you need to know the forward voltage of your LED's.
Assume the Red and Yellow have an average forward voltage of 2 to 2.2 volts.
Lets use 2 to simplify this. You have 4 LED's so add them up 2+2+2+2=8 volts.
Now we assume a supply voltage of 9v. Take the supply voltage and subtract the voltage drop of the LED's 9-8 = 1v.
Now we need to know how much current the LED can take.
the average LED's has an average max of 20 to 25 mA but that would very bright for this application.
Lets use 10mA that is .01A. Now lets do the math R= V/I or R = 1/.01. That works out to be 100 Ohms.
Typical resistor values range from 200 Ohms to 2kOhm for LEDs.
Figure your wattage now to get the right rating resistor.
P= I*E or P= .01*1 or .01W. You can use a 1/4W or even a 1/8W.
Check the math to be sure. I would probably use 1K 1/4w for a low light effect.

[Crontox102098]

LED's can be powered in series as has been suggested.
To figure the resistor you have to use a little Ohm's law and some basic math.
Using your diagram we will attempt to figure out an appropriate size for your resistor.
First you need to know the forward voltage of your LED's.
Assume the Red and Yellow have an average forward voltage of 2 to 2.2 volts.
Lets use 2 to simplify this. You have 4 LED's so add them up 2+2+2+2=8 volts.
Now we assume a supply voltage of 9v. Take the supply voltage and subtract the voltage drop of the LED's 9-8 = 1v.
Now we need to know how much current the LED can take.
the average LED's has an average max of 20 to 25 mA but that would very bright for this application.
Lets use 10mA that is .01A. Now lets do the math R= V/I or R = 1/.01. That works out to be 100 Ohms.
Typical resistor values range from 200 Ohms to 2kOhm for LEDs.
Figure your wattage now to get the right rating resistor.
P= I*E or P= .01*1 or .01W. You can use a 1/4W or even a 1/8W.
Check the math to be sure. I would probably use 1K 1/4w for a low light effect.

Surely! 470R is perfect to emulate this, even, if we use the red LED's with a clipping diode dist/overdrive could make it shine when we play the guitar.

[teemuk]

I hate to rain on this parade but, IMO, the outcome of this will look like orange and red LEDs mounted behind a grille, not like a vacuum tube. A vacuum tube does not look or even glow like a pair of small lamps. In fact, some of them actually have no glow whatsover so companies need to fit LEDs under them so that people wouldn't be dissapointed or erroneously believe the tubes must be bad.

If buying real vacuum tubes is not an option why not fit some random scrap metal inside a glass cylinder and then put the LEDs in some suitable location in the whole mess. It will probably look at least a bit more authentic.

[bool]

Just reverse enginner what behringer did.

[teemuk]

^ Behringer actually uses the tubes in the circuit, and very cleverly too may I add.

As said, they needed to fit additinal LEDs behind the tubes because in practice many real tubes do not glow in a manner people these days expect they should. Some may have filament hidden by other elements and therefore such tubes practically don't seem to glow at all.

...And these days that is (for some mysterious reason) a sure sign to people that the tubes must be bad. Today, tubes must glow ridiculously, so ridiculously that you need LEDs to actually give most of that effect.

Take a look around, Behringer is just one example out of many.
For example, this glow again practically comes from a LED fitted behind the tube:

In addition, the "pure valve distortion" is kinda misleading given that these units also utilise ordinary diodes to clip signal and dozens of solid-state gain and frequency shaping stages. In fact, lot less "bogus" in Behringer's tube units.

Another one... An AKG's tube microphone. See the nice tube glow....

...created by a LED fitted in to the tube socket. (I think they even patented this scheme, at least I remember that someone did).


If it glows prominently then most likely it's not a tube doing that.

[duck_arse]

once upon a time, if a valve (or toob) was glowing blue, you'd dive for the mains power switch quick fast. now, its seems to mean "everything's working fine here".

if you want tubes that light up, get some nixies. or one of those "dancing flame neon" fancy-candle bulbs.

[davent]

once upon a time, if a valve (or toob) was glowing blue, you'd dive for the mains power switch quick fast. now, its seems to mean "everything's working fine here".

if you want tubes that light up, get some nixies. or one of those "dancing flame neon" fancy-candle bulbs.

Better still for following signal dynamics, "magic eye" tubes.

[edvard]

Now there's an idea; 'dancing flame' bulbs and magic eye tubes for making a random-bubbly tremolo effect.

/edvard heads to the patent office...