I've got this 100W Peavey combo which I like to run from mains through 60W Light bulb. With the lower voltage it also has a sag and sounds great for recording. I tried Variac which lowers the voltage but that can't provide the sag. Is there something I could build in to the amp besides stuffig the light bulb inside?
I thought about resistor with heat sink which should act the same as the a light bulb, but my calculations come to 0.4A resistor which seems a bit small to me. Perhaps there are better options?
I thought about resistor with heat sink which should act the same as the a light bulb, but my calculations come to 0.4A resistor which seems a bit small to me. Perhaps there are better options?
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If you use a resistor, it'll will get as hot at the light bulb. It's probably easiest to use a halogen light and install it inside.
You're calculations cannot determine such a thing when it comes to a light bulb's resistance and/or impedence to the flow of electricity.
That's because the bulb's filament resistance varys widely depending on the current passing though it.
There is an initial "cold" resistance, being lower, and then a "hot-varying" resistance, - higher.
It's a nichrome filament suspended in gas.
Even a 100W lightbulb's varying resistance properties are different from another 100W of another brand.
Resistors, on the other hand, have a fixed resistance, designed that way.
Good point about the dynamic resistance of a light bulb vs a resistor.
I think you'll find light bulb filaments are made of tungsten though.
I think you'll find light bulb filaments are made of tungsten though.
One only uses a dim bulb tester as a quick go/ no-go test for gross faults. My recommendation to everyone using one is to use it initially to test for shorts, if the lamp is bright continuously for say <5-10s you have a fault that needs to be investigated with the power off. If the lamp dims, seconds after the initial surge. charging big ecaps you are good to short out the lamp or remove the DBT. running on a DBT continuously is not recommended , it can potentially damage or stress components esp if it has a soft start ckt.
Also use a larger wattage lamp >90w, these days they can be hard to come by but a heat lamp works just as well, as long aas it’s incandescent, halogen are okay but nothing electronic
Also use a larger wattage lamp >90w, these days they can be hard to come by but a heat lamp works just as well, as long aas it’s incandescent, halogen are okay but nothing electronic
Since lightbulbs have a varying resistance which increases with brightness, the slow-dimming effect and pulsating glow whenever heavy bass is fed to an amp, the lamp's resistance also is slow in its recovering.
It's sort of like compressing a sponge, or a pendulum of a clock... it's not instantaneous.
It's sort of like compressing a sponge, or a pendulum of a clock... it's not instantaneous.
I kinda doubt that using a bulb in series with an amp would cause much heat since the filament would not be fully lit 100% of the time with music.
Quiet passages, it would merely glow.
Why don't you fix the lamp permanently inside the combo? it's surely cool to have pulsating light when you play.
I'd install a switch to short it out if ever you needed the full blast.
If you really want some "electronic" solutions, try London Power: they sell boards to sag the high voltage of tube amps. Not cheap thought.
I'd install a switch to short it out if ever you needed the full blast.
If you really want some "electronic" solutions, try London Power: they sell boards to sag the high voltage of tube amps. Not cheap thought.
Agreed. It works and does what OP needs. If it aint broke then don't fix it.
I didn't know that light bulb resistance varies wildly. Sounds like I'll need to use it than. I'll look around if there are some small 60W ones. I've discovered this "phenomena" while restoring the amp as I always use light bulb tester. I forgot it was plugged in, played the amp and thought that the sound was too good to be true for Peavy until I realized it wasn't getting full power. I'm normally a tube amp player but this sounds pretty damn good for transistor. Yes it has less overall output but I don't care about that, it's not for gigging.
Just use the bulb.
If a combo, you can put it at the bottom, below the speakers, because you have free air flow there; I would not add another heat source inside a tube chassis or head.
No big deal to install a pencil type quartz halogen 75W "bulb" (nearest commercial size) inside a smallish (think 1/2 shoebox) perforated or ventilated metal box, floating in its center on a clip type ceramic socket.
If a combo, you can put it at the bottom, below the speakers, because you have free air flow there; I would not add another heat source inside a tube chassis or head.
No big deal to install a pencil type quartz halogen 75W "bulb" (nearest commercial size) inside a smallish (think 1/2 shoebox) perforated or ventilated metal box, floating in its center on a clip type ceramic socket.
Just use the bulb.
If a combo, you can put it at the bottom, below the speakers, because you have free air flow there; I would not add another heat source inside a tube chassis or head.
No big deal to install a pencil type quartz halogen 75W "bulb" (nearest commercial size) inside a smallish (think 1/2 shoebox) perforated or ventilated metal box, floating in its center on a clip type ceramic socket.
"pencil type quartz halogen" That's a great idea, that could fit almost anywhere. That would be nice and neat, I could even make a bypass switch for it. Thanks for the tip.
Funny, I suggested a halogen in the first reply to the thread 😀
Also, bipin is smaller than the linear.
https://www.amazon.ca/Pack-120Volts-GX6-35-75Watts-Halogen/dp/B00YNPL00M
Also, bipin is smaller than the linear.
https://www.amazon.ca/Pack-120Volts-GX6-35-75Watts-Halogen/dp/B00YNPL00M
True enough 🙂
That said, as far as heat sources are concerned, better "extended" (pencil) than point sources, if at all possible.
Also better outside chassis than inside.
Lower source density and free air flow help peace of mind 🙂
As somebody who had his shop burnt because of an overheated speaker drying oven (powered by lightbulbs, go figure), I am justified about being paranoid about the issue 🙂
That said, as far as heat sources are concerned, better "extended" (pencil) than point sources, if at all possible.
Also better outside chassis than inside.
Lower source density and free air flow help peace of mind 🙂
As somebody who had his shop burnt because of an overheated speaker drying oven (powered by lightbulbs, go figure), I am justified about being paranoid about the issue 🙂