I have a Cifte 12au7 tube that reacts to a specific led light when used in my bottlehead crack. When I shine the light on the tube I can hear a sound through my headphones. It sounds like a fairly pure tone. Anyone else come across tube behaviour like this? I'm no expert on tubes and have no idea how common this is. I don't have any other equipment to connect it to and it's the only tube that acts this way.
Photosensitive tubes
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randy@matrixq.com
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Tell me about the red light. How is it powered? Is it LED, compact flourescent, incandescent, neon, Xenon? How close does it need to be? Is it a high tone or a low tone?
My thinking is that it isn't the light but some electrical noise that the light source is producing.
My thinking is that it isn't the light but some electrical noise that the light source is producing.
It's actually not a red light but a LED light. It's a light on my phone that acts as a camera flash/ flashlight. At first I thought it would be interference from the phone, but if I hold the phone next to the tube facing the other way or just hold my finger in front of the light, no sound is emitted. No electromagnetic interference would be that uni-directional(well apart from the light of course).
The sound itself seems to be somewhere around 500hz and it changes from the left to the right channel depending on which side I point the light. The sound becomes audible with the light source at about 20cm or so.
The sound itself seems to be somewhere around 500hz and it changes from the left to the right channel depending on which side I point the light. The sound becomes audible with the light source at about 20cm or so.
Grainger49
New member
Randall is on the right path with his questions. He is asking about other known interferences that cause tube noise.
Phones often cause interference with tubes if they are too close. The same can be said of many computers. Can you try the phone without shining the light? That might nail it down.
Phones often cause interference with tubes if they are too close. The same can be said of many computers. Can you try the phone without shining the light? That might nail it down.
The phone with no light on doesn't cause any sounds no matter how close it is or whichever way it's oriented. Data transmissions to/from the phone do cause that pulsating noise we all should be familiar with. But during these tests I put the phone on airplane mode. I think I've exhausted all other possibilites, the light has to be the cause.
Grainger49
New member
Hmmmmm.... Interesting!
500 Hz is 2 mS -- if the LED is pulsed ON/OFF at appx 2 mS the LED would appear to be on continuously.
It is likely the LED is pulsed to save battery power. That could explain the 500 Hz.
If you have a LED flashlight, with a similar color light as your phone, try that.
The flashlight likely is not pulsed, and should not make a sound.
It is likely the LED is pulsed to save battery power. That could explain the 500 Hz.
If you have a LED flashlight, with a similar color light as your phone, try that.
The flashlight likely is not pulsed, and should not make a sound.
The cycling On/Off of a LED in a product that has some kind of smarts (a CPU or such), like a cell phone is a very common design technique. It a software/firmware solution to save battery power. Adjusting the frequency of the pulsing is a way to adjust brightness also (to a limit), or pulse slowly to indicate an error or alert.
Grainger49
New member
The pulsing is what allows the range to be found. Of course, a flashlight doesn't need range, so no pulsing. I'm guessing it is Doppler effect, the same as RADAR and LASER speed indicators.
I didn't think of the camera flash working better if the distance to subject was known, but for a plain ol' light source just to save power. Killing two birds with one stone so to say. Wonder how much battery life you would save if a flashlight had a simple circuit to pulse the LED? Or would the power required by the circuit to save power be a break even?
Grainger49
New member
Craig,
You got me there. With the current that an LED draws I would guess, and it is only a guess, that the pulse circuit would wipe out any savings since it would always be on.
You got me there. With the current that an LED draws I would guess, and it is only a guess, that the pulse circuit would wipe out any savings since it would always be on.
randy@matrixq.com
New member
Spock would say "Fascinating!"
If you have a camera or flash unit with a range finding red LED, you might be able to replicate the effect and confirm (to some degree) the pulse hypothesis.
This is definitely worth experimenting with.
If you have a camera or flash unit with a range finding red LED, you might be able to replicate the effect and confirm (to some degree) the pulse hypothesis.
This is definitely worth experimenting with.
Grainger49
New member
I hope to remember this when I sit down for some listening today. I'll get it all on and then focus my camera at different tubes, one at a time. My Canon has a green focusing light.
Ok,
I tried it with two cameras just now and both flashes do cause a sound, a short popping sound this time. One of the cameras has orange colored range finder led, but that didn't make any noise. Perhaps the led needs to be of the bright white variety.
I have a ne555 timer circuit connected to a red led, so I thought if I change the led to a white one and add a potentiometer to control the pulse time, I could perhaps create varying sound frequencies through the tube.
I tried it with two cameras just now and both flashes do cause a sound, a short popping sound this time. One of the cameras has orange colored range finder led, but that didn't make any noise. Perhaps the led needs to be of the bright white variety.
I have a ne555 timer circuit connected to a red led, so I thought if I change the led to a white one and add a potentiometer to control the pulse time, I could perhaps create varying sound frequencies through the tube.
I think it's hard to say if the camera flash interference was from light or the electromagnetic field or both.
With this in mind; is it the light or just the electromagnetic field?
Try optically filtering the light. Maybe dark paper.
555 timer and different light color:
Red to Blue would be pretty close to opposite ends of the visible spectrum.
If it really is just light; going just beyond visible, IR to UV could be interesting:
The data carrier frequency is probably too high to hear from an infra-red (IR) remote. I think the frequency is around 35 kHz.
If a Blue led works better than Red, then a ultraviolet diode could be interesting.
I have low power ultraviolet diodes at work (around 350-250 nm) I could bring home to try for grins.
OK that's why I listen in the dark - just kidding.
With this in mind; is it the light or just the electromagnetic field?
Try optically filtering the light. Maybe dark paper.
555 timer and different light color:
Red to Blue would be pretty close to opposite ends of the visible spectrum.
If it really is just light; going just beyond visible, IR to UV could be interesting:
The data carrier frequency is probably too high to hear from an infra-red (IR) remote. I think the frequency is around 35 kHz.
If a Blue led works better than Red, then a ultraviolet diode could be interesting.
I have low power ultraviolet diodes at work (around 350-250 nm) I could bring home to try for grins.
OK that's why I listen in the dark - just kidding.
Grainger49
New member
Tried my camera on all 6 tubes, nothing.
Ok, I did more experimenting.
I filtered the light with different colored paper. Results:
Plain white - sound still there
Red - nothing
Green - nothing
Blue - sound comes through, same as white paper
Inspired by this, I soldered a blue led to the timer circuit as I don't have any white ones. Success! Varying sound frequencies as I adjust the potentiometer. And this simple circuit should not be giving off any other electromagnetic interference like my phone possibly could have done.
As to why only this one tube makes noises, I heard an interesting theory. Perhaps there's a small amount of gas in the tube that is ionized by the light.
Maybe some you should get yourself these Cifte 12au7 tubes. Even if they don't all react to light, they're still very good sounding tubes : )
I filtered the light with different colored paper. Results:
Plain white - sound still there
Red - nothing
Green - nothing
Blue - sound comes through, same as white paper
Inspired by this, I soldered a blue led to the timer circuit as I don't have any white ones. Success! Varying sound frequencies as I adjust the potentiometer. And this simple circuit should not be giving off any other electromagnetic interference like my phone possibly could have done.
As to why only this one tube makes noises, I heard an interesting theory. Perhaps there's a small amount of gas in the tube that is ionized by the light.
Maybe some you should get yourself these Cifte 12au7 tubes. Even if they don't all react to light, they're still very good sounding tubes : )
