Pilot Light on an amplifier (electronics question)

Trevorus · #1 01-01-2007, 11:32 PM

It's a regular bayonet lamp, but I was wanting to change it to an LED. The source is approximately 3.2 volts AC. Would a simple bridge rectifier do the task?

Trevorus · #2 01-02-2007, 01:41 AM

Well, I decided to experiment. I ended up using a straight LED with a diode to protect against reverse voltage. Has a little bit of flicker that you notice if you pay attention, but it's not a problem for me.

bongomania · #3 01-02-2007, 02:41 AM

Shoot, I was hoping somebody would pop in with the "right" answer! I think the bridge rectifier was a good idea.

Trevorus · #4 01-02-2007, 12:02 PM

Quote:

Originally Posted by bongomania

Shoot, I was hoping somebody would pop in with the "right" answer! I think the bridge rectifier was a good idea.

Yeah, it's a good idea if you want a true DC output (albeit unfiltered), but in this circumstance, it's not all that necessary. The only difference is that the LED blinks at 30Hz, instead of 60Hz. I can see the difference, but it's not all that noticeable.

Jimi Cleek · #5 01-02-2007, 12:50 PM

Ok so now take a different colored led and put it in parallel but reverse polarity with the original.

Jimi

TrooperFarva · #6 01-02-2007, 01:08 PM

Quote:

Originally Posted by Trevorus

Well, I decided to experiment. I ended up using a straight LED with a diode to protect against reverse voltage. Has a little bit of flicker that you notice if you pay attention, but it's not a problem for me.

What do you mean you used a straight LED with a diode?

Phat Ham · #7 01-02-2007, 01:41 PM

Quote:

Originally Posted by TrooperFarva

What do you mean you used a straight LED with a diode?

I was gonna ask the same question. An LED is a diode.

Trevorus · #8 01-02-2007, 01:44 PM

Quote:

Originally Posted by Phat Ham

I was gonna ask the same question. An LED is a diode.

LED's don't handle much reverse current, whereas a regular diode can handle more. I use a regular diode to block reverse voltage, and make sure the LED doesn't burn up.

I also used current limiting resistors to extend the LED's life. It's marginally dimmer, but it will keep the LED going for a long while.

Trevorus · #9 01-02-2007, 01:44 PM

Quote:

Originally Posted by Jimi Cleek

Ok so now take a different colored led and put it in parallel but reverse polarity with the original.

Jimi

That's not a bad idea... Except it has a purple jewel. It's not a regular LED through panel setup.

RWP · #10 01-02-2007, 01:57 PM

If I recall correctly a diode will have a forward voltage drop of 0.7v. So you really have 2.7v across the LED. Did you use current limiting resistor?

This might help.

http://ourworld.compuserve.com/homep...Bowden/led.htm

Trevorus · #11 01-02-2007, 02:05 PM

Quote:

Originally Posted by RWP

If I recall correctly a diode will have a forward voltage drop of 0.7v. So you really have 2.7v across the LED. Did you use current limiting resistor?

This might help.

http://ourworld.compuserve.com/homep...Bowden/led.htm

Yes to the resistors. See above.

What I am wondering is, will a diode bother the filament circuit on a tube amp? Because that is what this is connected to. All tubes seem to warm up properly, and the amp sounds fine (fantastic, in fact).

RWP · #12 01-02-2007, 02:19 PM

Quote:

Originally Posted by Trevorus

Yes to the resistors. See above.

What I am wondering is, will a diode bother the filament circuit on a tube amp? Because that is what this is connected to. All tubes seem to warm up properly, and the amp sounds fine (fantastic, in fact).

I don't think that will be a problem. The LED should only be pulling about 15-20Ma, a small fraction of the current available to the tube filaments.

Trevorus · #13 01-02-2007, 09:39 PM

Here's how it looks!

Rattman · #14 01-02-2007, 10:58 PM

Quote:

Originally Posted by Trevorus

Here's how it looks!

Yeahey! That LED under the old jewel apparently turned out just fine. I chuckled when you mentioned the LED is responding to the 30HZ portion of either the negative or the positive remainder of the AC sine wave post diode-filtering upstream from your new LED. Pretty kool...pretty kool indeed.

Neat solution.. I love it.

Phat Ham · #15 01-02-2007, 11:42 PM

Quote:

Originally Posted by Trevorus

LED's don't handle much reverse current, whereas a regular diode can handle more. I use a regular diode to block reverse voltage, and make sure the LED doesn't burn up.

I also used current limiting resistors to extend the LED's life. It's marginally dimmer, but it will keep the LED going for a long while.

ah i see what you did. You might as well make your rectifier complete by adding the cap and filtering out the AC.

Trevorus · #16 01-02-2007, 11:56 PM

Quote:

Originally Posted by Phat Ham

ah i see what you did. You might as well make your rectifier complete by adding the cap and filtering out the AC.

Nah, I think the 30Hz flicker is not noticeable, and I used the original bayonet base from the blown bulb in order to retain originality. There's just no more room in there.

TrooperFarva · #17 01-03-2007, 05:04 AM

Quote:

Originally Posted by Trevorus

Nah, I think the 30Hz flicker is not noticeable, and I used the original bayonet base from the blown bulb in order to retain originality. There's just no more room in there.

Wouldn't it be 60Hz flicker? You're eliminating have the wave, but that half of a wave still has a frequency of 60Hz. If you threw in a bridge rectifier, and used both halves of the wave, but did not filter it, then the LED would light up at 120Hz, because essentially, it'd have forward bias twice each cycle. Or am I thinking about this wrong?

Trevorus · #18 01-03-2007, 09:35 AM

Quote:

Originally Posted by TrooperFarva

Wouldn't it be 60Hz flicker? You're eliminating have the wave, but that half of a wave still has a frequency of 60Hz. If you threw in a bridge rectifier, and used both halves of the wave, but did not filter it, then the LED would light up at 120Hz, because essentially, it'd have forward bias twice each cycle. Or am I thinking about this wrong?

I think you may be right... possibly. 1Hz is a vibration back and forth in a second. So, really the cycle is back AND forth. I forgot about that. So, it really is 60Hz. Thanks for pointing that out!

TrooperFarva · #19 01-03-2007, 05:40 PM

Quote:

Originally Posted by Trevorus

I think you may be right... possibly. 1Hz is a vibration back and forth in a second. So, really the cycle is back AND forth. I forgot about that. So, it really is 60Hz. Thanks for pointing that out!

I wasn't sure myself, I was just throwing it out there. Good work though, the LED is a cool idea.