Question:
ok so i read somewhere that you can use a lightbulb as an attenuator, so if my amp is 100W i'd just use a 100W lightbulb. but is this even true? how would i do that if it's possible.
thanks
Answer:
Usually. Tube. Amps. Only.
Answer:
I have no idea how you would use a lightbulb as an attenuator...
actually I do, because an attenuator is basically a big resistor, and a lightbulb is also just a big resistor. I just couldn't imagine rigging up a 100W lightbulb in the back of an amplifier...can we say heatstroke?
Answer:
Originally Posted by thesteve I have no idea how you would use a lightbulb as an attenuator...
actually I do, because an attenuator is basically a big resistor, and a lightbulb is also just a big resistor. I just couldn't imagine rigging up a 100W lightbulb in the back of an amplifier...can we say heatstroke?
i heard of someone doing it with a valve junior,
besides your shredding away and the light bulb blinks to the beat, kinda sweet eh?
I'd just make a box to sit on my amp with a bulb and roll cage around it. with the plugs for the amp, i guess
the simple design would mean that if a bulb burned out you just screw in another one
would it just be wired in series or what
i dont know how it would work
Answer:
Originally Posted by Building429_Boy Usually. Tube. Amps. Only. what are you talking about
Answer:
I don't know if the bulb would quite go with the beat. Basically, you'd have to wire it in such a way that the signal goes from your amp-->lightbulb-->speaker.
Answer:
Originally Posted by thesteve I don't know if the bulb would quite go with the beat. Basically, you'd have to wire it in such a way that the signal goes from your amp-->lightbulb-->speaker.
well i guess the louder you play the brighter it gets
Answer:
Originally Posted by jmjlai well i guess the louder you play the brighter it gets yeah...i can see how it works...I think something fun though probably very dangerou thing to do would be to use a 30W bulb on a 100W amp...haha.
Answer:
somehow i see this as a really bad idea...
what happens when the lightbulb burns out? don't tube amps fry when they aren't attached to load?
Answer:
Originally Posted by What5647 somehow i see this as a really bad idea...
what happens when the lightbulb burns out? don't tube amps fry when they aren't attached to load? yes, but it's not an instantaneous process
Answer:
Originally Posted by jmjlai the simple design would mean that if a bulb burned out you just screw in another one
would it just be wired in series or what
i dont know how it would work
You can't very well use the same speaker and a lightbulb -- you'd mess with the impedance.
Lets say your amp's speaker is 8 ohms and the lightbulb is 8 ohms. In series, it'd be 16 ohms total. In parallel, it'd be 4 ohms.
If your amp takes 8 ohms and you have a 4 ohm speaker and 8 ohm lightbulbs, you could hook it up with the 4 ohm speaker in series with 2 8 ohm lightbulbs in parallel with each other. That would cause the 2 light bulbs to have an equivalent resistance of 4 ohms, added with the 4 ohms from the speaker gets you back to 8.
(very bad ascii drawing)
8 ohms simply used as an example.
FYI, a 100w bulb resistance should be:
p=i * e
100w = i (120V)
i = ~0.83A
e = i * r
120v = 0.83A * r
r = ~144.6 ohms
Wattage will change resistance, but this seems to be a pretty 'iffy' system to rig up. I don't think I'd risk an amp's output transformer and the rest of my power amp to it, at least not without some serious testing first.
Answer:
Originally Posted by tht00 FYI, a 100w bulb resistance should be:
p=i * e
100w = i (120V)
i = ~0.83A
e = i * r
120v = 0.83A * r
r = ~144.6 ohms
Wattage will change resistance, but this seems to be a pretty 'iffy' system to rig up. I don't think I'd risk an amp's output transformer and the rest of my power amp to it, at least not without some serious testing first. From what I understand, the power amp on most amps will handle going in an upward direction (increased impedance), though I don't know to what limit that holds true. Perhaps if I ever get the amplifier chip replaced in my little Crate GFX-15 I'll have to run some tests on it.
Answer:
Seems like you'd have next to nothing left of the power if your impedance went up that high.
Throwing out the possibility of frying an amp with no load on it when the bulb burns out.......think about speakers and your ears, too. If I had my Classic 30 cranked up to 6 or 7 with the attenuator in the circuit (when a non-attenuated level would be 2 or 3 at the very most) just think at what it could/would do to the speaker and my hearing if that attenuator (i.e. the light bulb blowing) were instantly taken out of the circuit.
Answer:
I'm sure the speaker would be fine...your hearing on the other hand...that's a good point.
Answer:
um guys... if the light bulb blows the load is removed, no volume gets to the speaker. Solution? Wire in hefty resistors in case the bulb blows, so that it actually gets to the speaker, but normally takes the path of less resistance.