Hi there,
I hope I used the correct english word here....
I measured the wattage on some Fender 6L6 amps 40 Watt amps.
I got like a household meter pluged between the wall and the amp and it tells me that the amp is using about 80 watts (turned on, no playing).
If I play, it goes up very little (or the display might be to slow to show peaks...) like to 85 watts.
If I divide the wattage with the voltage I calculate like .36 Ampere with 220V or .72 Ampere with 110V.
The fuse on vintage Fender amps are 2 Amp Slo-Blo (even my Tweed Deluxe has 2 Amp fuse).
Way higher than needed in operation.
So I guess when the amp is switched on it pulls a lot of current to load the main filter caps?
Like in a short peak?
What would be the maximum current? The fuse is Slo-Blo, so how much higher can it go in a peak than it´s nominal value?
I do not know how the measure this peak without an memory oscilloscope.
Any info welcome!
The reason I am asking is because I bought a "power conditioner" where I can adjust voltage and hz.
Found it on a rig rundown of AC/DC (around minute 9:30) :
https://www.youtube.com/watch?v=j5C7GKGxICg
Mine is just way smaller and a chineese brand with 2 Amp max.
I have heard others and they do make a huge difference in sound.
Many travelling musicians are using those to have the same sound every night.
If you have information what other brands can be used, please let me know!
cheers,
Stephan
switch-on current
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pompeiisneaks
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Re: switch-on current
First don't confuse the watts the amp 'uses from the wall' vs the output wattage.
The output wattage is what hits the speaker. This is different because the system loses a lot of the power input as heat to the tubes and inefficiencies of the amplifier etc. Or at least that's my understanding.
SO the 85 W you're seeing or 80W may be pretty common. Yes the current is going to spike initially where the tubes aren't yet conducting and the caps are charging. The decision on the amp's fuse is based upon what is obvious excessive current to a level that should protect the amp from damage, but well beyond normal operation. If the amp was to go to say 3 amps and stay there too long, you're likley to roast too many things like tubes, OT's etc. This is calculated to ensure it's in a 'safe' zone, but even then sometimes amps fail despite the fuse, as they may run at 1.5W for too long due to a more minor fault but end up causing bad things.
Ultimately, though it should protect against most failures. The even better solution is to often put a B+ fuse on to protect against that part of the amp and it can be a bit closer to the operating range as that almost never goes over the expected current of the tubes, unless a tube is failing.
As for your device, it's often better to have it have a slightly higher headroom than the expected use, but since youv'e seen the 2A is a pretty high threshold you're likely to be fine.
As for a voltage conditioner like that, it can be very helpful especially at many venues where the power supply is crap
~Phil
The output wattage is what hits the speaker. This is different because the system loses a lot of the power input as heat to the tubes and inefficiencies of the amplifier etc. Or at least that's my understanding.
SO the 85 W you're seeing or 80W may be pretty common. Yes the current is going to spike initially where the tubes aren't yet conducting and the caps are charging. The decision on the amp's fuse is based upon what is obvious excessive current to a level that should protect the amp from damage, but well beyond normal operation. If the amp was to go to say 3 amps and stay there too long, you're likley to roast too many things like tubes, OT's etc. This is calculated to ensure it's in a 'safe' zone, but even then sometimes amps fail despite the fuse, as they may run at 1.5W for too long due to a more minor fault but end up causing bad things.
Ultimately, though it should protect against most failures. The even better solution is to often put a B+ fuse on to protect against that part of the amp and it can be a bit closer to the operating range as that almost never goes over the expected current of the tubes, unless a tube is failing.
As for your device, it's often better to have it have a slightly higher headroom than the expected use, but since youv'e seen the 2A is a pretty high threshold you're likely to be fine.
As for a voltage conditioner like that, it can be very helpful especially at many venues where the power supply is crap
~Phil
tUber Nerd!
Re: switch-on current
A while back when I was curious about the subject of fusing I found that it was much more complicated than I had originally thought. There are many, many parameters a fuse has beyond just it's current rating. Things like:
https://www.littelfuse.com/~/media/elec ... de.pdf.pdf
I'm sure there are whole textbooks written on the subject
.
In the end the primary job of the mains fuse in a guitar amp is to keep your house from burning down. As a side effect, it may also protect other components in your amp. But that is not really it's main job. Other fuses inside the amp (such as on the B+) are often put in to try and protect the amp itself.
In addition to all the varied fuse parameters a designer must also consider the varied current requirements put into the fuse by the amp. And a balance needs to be made between setting the fuse's current rating too low (it blows when it does not need to and causes angry customers) and too high (fire hazard). I would guess most guitar amp fuses are a bit higher than they need to be to avoid angry customers.
One could experiment with lower rated fuses and increase the safety. At some point the fuse will start to blow too frequently (because of all the varied parameters mentioned above). But, it would be a very bad idea to increase the fuses current rating above what the manufacturer specifies unless you are also an E.E. and think you have studied the circuit (including thermodynamic properties) at least as well as the original engineer.
- Voltage rating (over this rating the fuse may blow and still conduct an arc)
- Operating temperature range (heat changes the characteristics of all fuses)
- How fast the fuse opens.
- ...
https://www.littelfuse.com/~/media/elec ... de.pdf.pdf
I'm sure there are whole textbooks written on the subject
.In the end the primary job of the mains fuse in a guitar amp is to keep your house from burning down. As a side effect, it may also protect other components in your amp. But that is not really it's main job. Other fuses inside the amp (such as on the B+) are often put in to try and protect the amp itself.
In addition to all the varied fuse parameters a designer must also consider the varied current requirements put into the fuse by the amp. And a balance needs to be made between setting the fuse's current rating too low (it blows when it does not need to and causes angry customers) and too high (fire hazard). I would guess most guitar amp fuses are a bit higher than they need to be to avoid angry customers.
One could experiment with lower rated fuses and increase the safety. At some point the fuse will start to blow too frequently (because of all the varied parameters mentioned above). But, it would be a very bad idea to increase the fuses current rating above what the manufacturer specifies unless you are also an E.E. and think you have studied the circuit (including thermodynamic properties) at least as well as the original engineer
.Re: switch-on current
Yes, what they said.
Also what you guessed at - there is a very short, sharp peak of current when the amp is first powered up. When you turn an amp on, the power transformer is not "charged up" with a magnetic field, and the main filter capacitors for the DC power supply are at zero volts. So when you first turn on the AC, the AC power has to instantly charge up those things to get the amp to operating. It is not unusual for a large transformer all by itself to pull over 20A in a single peak if you accidentally turn it on at the wrong place in the AC power line sine wave.
Also what you guessed at - there is a very short, sharp peak of current when the amp is first powered up. When you turn an amp on, the power transformer is not "charged up" with a magnetic field, and the main filter capacitors for the DC power supply are at zero volts. So when you first turn on the AC, the AC power has to instantly charge up those things to get the amp to operating. It is not unusual for a large transformer all by itself to pull over 20A in a single peak if you accidentally turn it on at the wrong place in the AC power line sine wave.
"It's not what we don't know that gets us in trouble. It's what we know for sure that just ain't so"
Mark Twain
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martin manning
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Re: switch-on current
And add to the above the low resistance and therefore high current draw of cold filaments.
Re: switch-on current
Assuming you have a reasonably accurate 'wattmeter' on your AC mains input and it reads about 80-85W, then you can't simply use watts and volts to derive operating rms current, as the power factor won't be one.
Your power meter may indicator a power factor (PF) value, although that value may not be accurate, as it needs to take in to account the phase shift between the voltage and current waveforms, and also the distortion of those waveforms. A PF less than 1 will mean that more current flows than just the value you calculate from Watts and Volts - and the current level can be substantially more. In essence, a more accurate measurement for fuse determination is the rms current, which may be available from your wattmeter.
For most such amplifiers, the fuse should definitely be a time-delay 'T' rated fuse. Depending on your fuse supplier, you may have available IEC rated fuses, or american style UL rated fuses - they have different rating capabilities with respect to the continuous current level (ie. a 2A UL fuse is equivalent to a 1.6A IEC fuse for continuous rating). I recommend you use a fuse that has a confirmed UL or IEC rating, and not just a fuse from a spare parts bin.
One reference that may be of assistance:
https://www.dalmura.com.au/static/Valve ... fusing.pdf
Your power meter may indicator a power factor (PF) value, although that value may not be accurate, as it needs to take in to account the phase shift between the voltage and current waveforms, and also the distortion of those waveforms. A PF less than 1 will mean that more current flows than just the value you calculate from Watts and Volts - and the current level can be substantially more. In essence, a more accurate measurement for fuse determination is the rms current, which may be available from your wattmeter.
For most such amplifiers, the fuse should definitely be a time-delay 'T' rated fuse. Depending on your fuse supplier, you may have available IEC rated fuses, or american style UL rated fuses - they have different rating capabilities with respect to the continuous current level (ie. a 2A UL fuse is equivalent to a 1.6A IEC fuse for continuous rating). I recommend you use a fuse that has a confirmed UL or IEC rating, and not just a fuse from a spare parts bin.
One reference that may be of assistance:
https://www.dalmura.com.au/static/Valve ... fusing.pdf