I learned something new today that was unexpected. I never knew why two fuses with the same amp rating could look different. This is one of the reasons why I like your channel. Another is that your voice and the cadence which you speak with are just relaxing and drama free.
Hey Lyle. I'm an electrical engineer and your graphical representation of AC current through the input fuse is exactly correct.....no changes needed :-)
I was thinking the same thing but wasn't 100% sure so glad to confirm it. If you were measuring voltage and current on a scope, they would look the same just at different magnitudes depending on scale of each channel on scope. Only other difference would be phase, which may change in the initial inrush state to steady state
Visual indicators of a slo-blow or "timed" fuse: the fuse element is spiral wrapped around some kind of fiberglass-like core ( as shown in the video); the fuse has a coiled spring and what looks to be a resistor inside of it; the fuse element appears to be a thin wire as is commonly seen in an ordinary fast blow fuse but also has what looks like a blob of solder in the middle of it. This last type of slow blow fuse is most commonly seen in in 5 by 20 mm, miniature F type fuses, and are typically marked with a T on one of the end caps, which stands for "timed".
While we are discussing current surging at turn on, which tend to blow fuses for no apparent reason, this is the purpose of the thermistor (black disc) seen on the power-switch PCB of the Supro amp. The thermister has a high resistance when at room temperature and increases the total resistance of the power transformer primary circuit so that it doesn't draw as much current when you turn the amp on; the thermistor lowers in resistance as it heats up and it takes itself almost out of circuit in a few minutes, but they run hot enough to burn your fingers for the entire time that the amplifier is turned on..The location of that thermistor on the same small PCB that holds the the on-off switches and LED is a bad idea. The heat generated by the thermistor will likely cause premature failure of the solder joints around it and cause oxidation of the spade lug connectors. I'd recommended relocating it to where the power cord enters the amp, and put it on its own terminal strip.
Thanks for that mate, l own a BK 12 & it definitely throws out more heat than my EL84 amp (made by a local bloke)... I've put a small clip on fan at the back of the Supro in the hope it'll help cool it somewhat, but I'll look into getting it mounted separately. Barring how warm it gets, it's a gd little amp.
Your current waveform illustration is good and probably the best way to show how inrush current affects fuses. As you know, the inrush current is mostly due to charging of filter capacitors (plus some due to extra startup current through tube filaments). Your diagram is generally correct for amps with solid state rectifiers, except that the inrush current lasts for many more ac cycles. Note that there is no voltage surge since utility power is a constant ac voltage source. Things are more complicated with tube rectifiers because the inrush current through the rectifier increases as the rectifier tube warms up, then decreases as the filter capacitors become charged. The inrush current stresses not only the fuse, but of course also the power transformer and the rectifier. As you know, that is why it is not a good idea to replace filter capacitors with ones of larger capacitance, and why solid state rectifiers need to have a resistor (or inrush current limiter) ahead of the filter capacitors.
My wake up call was when one of my precious tube vintage 50's tube amp fried the trannies and saw wall voltage was at 130. Now always use an AmpRx Brown Box/Brownie to dial in AC (suggest something like this) to the AC level that the amp was designed for. Many of the older amps are marked 117vac max, so figures they run best at the designed power levels. Even seen new amps label 117v.
Good stuff! I think your representation is good on paper, however I have an old school amp meter on my variac, and when I switch it on, you can see the meter bounce high then rapidly settle once the standby is switched to operate mode (in correctly running and typical situations). So, a traditional amp meter (a meter with a needle) will demonstrate it for you perfectly. Old style meters work better translating current in those kinds of situations. Mine goes to 5 amps, and I have my variac loaded with a 5 amp fast blo in it - so it works for most 100w or less tube amps. Solidstate amps can climb in amperage quite a bit, so larger amps, bass amps, power amps can overpower my smaller variac. I have a 10 amp variac too, but I don't have an amp meter wired into that one (not yet anyway). There are many reasons for a power fuse to blow, most often tubes, but can be transformers, shorted diodes, other shorts. Another indicator for a slow blow type is a T (for time delay) stamped on the fuse itself. HT fuses are usually fast blow.
Great video as always, keep up the great good work. The amp would obviously benefit from a “Quantum Science Audio Silver Extreme Level fuse” only $4500 per fuse🤣🤣🤣🤣🤣
Here are a couple of technical reasons why a fuse might fail for what seems to be no particular reason: 1) power transformers will appear to be almost a dead short circuit before they are energized and build a magnetic field in and around the copper coils/windings and iron laminations (you can confirm this with an Ohmmeter connected to the power cord of your amp; the primary of the power transformer probably measures only a couple of ohms). 2) The electrolytic filter caps connected to the secondary of the power transformer also will appear to be almost a dead short if they are discharged (which is usually the case if the amp has been sitting around unused for a few hours or days). And 3) The heaters of all the tubes have an extremely low resistance when they're cold and draw a lot of current until they heat up, And because the heaters are all wired in parallel, the more tubes the amp has the lower the combined resistance of them all. When you turn the amp on you will draw a large amount of current for a few seconds as the filter caps charge and the tubes start to heat up (the resistance of the tube heaters increases enormously when they're warm to hot, and the filter caps no longer present a dead short circuit once they are charged). The inductive nature of the power transformer not only acts almost as a dead short when you first energize it, drawing a large amount of current, but because it is building a magnetic field the voltage going into it at turn-on actually overshoots and goes higher than the incoming wall voltage! Visualize the 60 hz AC as having 120 peaks of full voltage per second, and 120 dead spots per second where the voltage is at zero. Depending where the cycle of the wall voltage is at when you flick the switch and turn the amp on, you will have either a lesser or a greater inductive surge as the power transformer inductance charges. If you could somehow turn the amp on only when the AC voltage is at one of those peak points (one of the 120 times per second that it reaches peak voltage), the inductive surge would be minimal, but if you randomly happened to turn it on just as the wall voltage is slightly above zero and heading to its full peak, you'll induce a huge inductive ringing and voltage overshoot into the transformer, and that's when current draw is the greatest. All of the above surge-producing scenarios detailed above will tend to weaken a fuse over time, and of course invariably it will fail not when you're practicing but at a gig. Always carry fuses of the correct value and type with you to your gigs and practice jams, and don't buy cheap-ass, no name or possibly counterfeit fuses off of eBay, Amazon or Alibaba!
Imagine you have a bucket full of marbles and an empty bucket sitting on a table. The marbles represents electrons. When the two buckets are on the table the potential to do work is zero or zero volts. The bucket on the table represents the ground state. Lift the marble bucket up, the potential rises. Start to pour the marbles out. The marbles moving out of the bucket represent amperage, the number of electrons moving past a certain point during a period of time. From that fixed height, pour a little faster. The amperage(intensity)has increased but the voltage(potential) has remained the same. Lift the bucket higher, and return to the original rate of dropping marbles. The potential has gone up but the amperage has dropped. You can now describe both properties of electron flow in one motion. Introduce an interceptor bucket to demonstrate a lift ground or a voltage dropping circuit.
I would be hesitant to plug in any electrical devices into a generator. Unless it was an inverter type.large enough to handle a bigger load than what's connected. That's just me..but if you gotta gig it,,ya takes your chances..great channel, certainly one of my favs.
Hey Lyle, the sine wave representation of current is accurate, in that it is a time domain representation of the amount of electrons flowing through the circuit. I know you know all of this, but maybe some of your viewers will appreciate the background. If we look at the simple version of Ohm's law, Voltage is equal to Current multiplied by Resistance (or V=IR, and yes current is represented by an I because French), the sine wave representation makes sense. This is because (generally speaking) the resistance of the circuit does not change, so as the voltage rises and falls, the current has to rise and fall to "obey" Ohm's law. For a general example, since the resistance is constant we can pick any number we want, so lets say it is 1. Then we get Voltage=Current x 1, or simply Voltage=Current, so the graph of the two would be identical, hence a sine wave is correct for both. If the resistance is anything other than 1, the graph of the current would just have taller or smaller waves than the voltage.
Thanks Leigh. Great explanation. I knew that was the case here but expected to get pilloried for using such a simplified visual representation. In working on amps I myself think of the circuits as being weights and the fuses/wires/traces as being the strings that hold the weights up. For instance, take an amp with a 6L6 and two 12AX7s. For the heater supply, the “string” supporting all four tubes needs to be able to handle the full “weight” of 2.7A (all the tubes). But if the tubes are wired in a parallel sequence as usual, the wire “string” to the last 12AX7 only needs to support the “weight” of 300mA.
@@PsionicAudio Thanks Lyle, the weight analogy is interesting, I had never thought of it that way! Quick question for you, I am looking to build my first fuzz face (actually I plan on making a few for friends as well, maybe 10 total) and I'm wondering if you know of a good source for components. I read the mojo components articles on your web site and I have a Mouser cart filled up with most of the circuit components (although I am not sure which 22 uf capacitor to get for the fuzz control), but the 3PDT switches, enclosures, pots, and jacks seem quite over priced. Do you have any recomendations for a decent place to get lower quantities of those parts, and which ones are the most reliable? Thanks again for all your great videos!
Thank you very much for fuse explanation. I think I heard your intestine gurgling @ 15:36, my 79 Super Reverb that I just got about 1 month ago just blew a fuse, what are the basics to check first? or do you recommend a video episode I missed… thx again 😊
Current would be out of phase with the voltage. If I dig out the clamp on Tektronix current probe for inductively measuring current, and I can finagle a fancy digital O Tek scope I can show the voltage and the current in two colors. If I get super lucky one of their scopes will actually do a 3D display of the voltage & the current, and it looks really cool. It's not $130,000 cool so I don't own that O scope.
I prefer short bat switches, specifically Carling brand, for power and standby. I just think they look cooler, and classier. Also there is less length sticking out to be hit, bumped, broken off....and whatever else can happen.
Was always curious about whether I should use slo-blow or fast blow fuses in my amps. Thanks for clarifying. That said, it sounds based on your discussion, as there are different ratings on slo-blow fuses (MTD vs ???); medium, slow or fast, I presume.
For our purposes, fusing audio amplifiers and guitar amplifiers, ceramic fuses probably aren't necessary or advantageous. Ceramic resistors are typically sandfilled and they are designed to be "explosion proof". If you have some kind of industrial piece of equipment that might accidentally get hit with a massive voltage or current surge, many times it's normal operating points, an ordinary glass fuse could not only explode but also cause vaporized metal to be deposited all around the inside of the device causing arcing and short circuits and further damage. Expensive, high quality test equipment ( such as a Fluke multimeter) will often use sandfilled fuses (often large, epoxy fiberglass fuses, not ceramic) for protection so that you don't spatter metal around the inside of the meter by connecting it to a high voltage while the meter is set in the low voltage range, or measuring voltage when its set for amperage, and so on. The commonest place I see factory-installed ceramic fuses, fast or slowblow, in audio gear is in big power amps that put out several hundred watts or more, with fuse values ranging from 8 to 20 amps. Not really necessary in most guitar amps, that are typically fused at 3 amps or less. Perhaps a good idea if you gig a lot at outdoor shows that are run from a generator?
All that, with the addition that glass fuses can fail if they get too hot, no matter the actual current. That might be what happened to the first tube in this amp.
@@PsionicAudio , hmmm... I haven't heard this before. Are we referring to glass fuses getting hot from internal heating, or from ambient heat inside the amp, or both? If anything I would expect that glass fuses would allow infrared radiation/ heat to escape just as heat radiates out from vacuum tubes (athough the glass would also let heat enter equally well); ceramic fuses would tend to trap and hold any internal heat generated due to resistance in the element, and adding sand inside the ceramic fuse as an Electrical insulator also means that it is a Thermal insulator. Now if you want to prevent ambient heat from entering the fuse, the reflective surface of the white ceramic is probably much better than glass for that purpose. This is an interesting discussion, or perhaps quandary. And by the way I have seen heat-stressed fuses become resistors that measure several several dozen ohms . Personally I think most people would probably prefer the glass fuse because most of the time even a layman can tell at a glance if it is blown. Also you might see the fuse element to be sagging a little bit as if it has stretched and this too indicates it needs to be replaced. But as every technician knows , visual inspection of a glass fuse can fool you and sometimes they are bad even though they look OK. A ceramic fuse of course requires you to get out the multimeter.
Ive been using fast blow fuse as its much easier and cheaper to purchase(im from the Philippines), im using the correct fuse rating with respect to what the circuit calls for and so far i havent blown a fuse yet. Is it safe to say that i havent had a current/voltage swing thats too drastic thats enough to blow it yet?
It all depends on the amp. One amp might “need” a 1.1A fuse. Another might “need” a 1.85A fuse. Both amps will use the next standard rating up, so both amps will use 2A fuses. The first amp asks less of that 2A fuse than the second amp. Hope that makes sense.
Completely unrelated, but I figured I'd ask: I have a Monster Pro 7000 MK2 power conditioner in my studio. It has 2 Amp Slow Blow for audio and digital and a 10 Amp Slow Blow for video. Are these 250V or 125V. I can't find the information ANYWHERE online. Please help!
Most fuses are rated at 250v. It’s not like amperage as in you can put a higher rated voltage fuse in and be fine. The amperage is the important rating here
There's no need to show the sine wave because the fuse reacts only to the RMS (equivalent DC) current anyway. A 12AX7 I just checked measures ~3.5 ohms cold resulting in 1.8 amps, six times the current cold, and it takes a few seconds to drop all the way down to its rated 0.3 amps. Meanwhile, the power supply capacitors look like a short until charged limited only by the minimal inductance of the transformer windings, which is an additional challenge with solid state rectifiers. The fuse time/current curves are available on line. (see www.mecampbell.com/media/pdf/ID-SPE-Bus_Ele_DS_2004_MDL_MDL-V.pdf) To the commenter using up-sized fast-blow, that's short circuit protection but no overload protection, which is hardly any protection. All you are doing is protecting the house fuse, not anything inside your amp. That amp could get hot enough to literally be in flames by the time the failure escalates to short circuit levels, typically because insulation melts. We engineers call this fuse coordination - the fuse time current curve must be matched as close as you can to the load's time current curve without crossing for optimum protection.
Do you have a better suggestion for visually representing current for musicians to understand? PS musicians - I consider myself one. This is not about musicians being “dumb” - it’s about a specialized vocabulary.
@@PsionicAudio The only "water through a hose" analogy I can think of would be a hose with a weak point -- a bottle neck or a hernia -- that cuts out if the pressure exceeds the wall limits. Not sure that would really clarify much. As a side note, it's not easy to find a slow blow fuse at the local home despot or lowest, between what they stock (especially in the Amp range you might need) and inscrutable labels and codes.
I learned something new today that was unexpected. I never knew why two fuses with the same amp rating could look different. This is one of the reasons why I like your channel. Another is that your voice and the cadence which you speak with are just relaxing and drama free.
Hey Lyle. I'm an electrical engineer and your graphical representation of AC current through the input fuse is exactly correct.....no changes needed :-)
I was thinking the same thing but wasn't 100% sure so glad to confirm it. If you were measuring voltage and current on a scope, they would look the same just at different magnitudes depending on scale of each channel on scope. Only other difference would be phase, which may change in the initial inrush state to steady state
In the water, buckets and pipes analogy, water hammer may be the best best metaphor.
Visual indicators of a slo-blow or "timed" fuse: the fuse element is spiral wrapped around some kind of fiberglass-like core ( as shown in the video); the fuse has a coiled spring and what looks to be a resistor inside of it; the fuse element appears to be a thin wire as is commonly seen in an ordinary fast blow fuse but also has what looks like a blob of solder in the middle of it. This last type of slow blow fuse is most commonly seen in in 5 by 20 mm, miniature F type fuses, and are typically marked with a T on one of the end caps, which stands for "timed".
While we are discussing current surging at turn on, which tend to blow fuses for no apparent reason, this is the purpose of the thermistor (black disc) seen on the power-switch PCB of the Supro amp. The thermister has a high resistance when at room temperature and increases the total resistance of the power transformer primary circuit so that it doesn't draw as much current when you turn the amp on; the thermistor lowers in resistance as it heats up and it takes itself almost out of circuit in a few minutes, but they run hot enough to burn your fingers for the entire time that the amplifier is turned on..The location of that thermistor on the same small PCB that holds the the on-off switches and LED is a bad idea. The heat generated by the thermistor will likely cause premature failure of the solder joints around it and cause oxidation of the spade lug connectors. I'd recommended relocating it to where the power cord enters the amp, and put it on its own terminal strip.
Thanks for that mate, l own a BK 12 & it definitely throws out more heat than my EL84 amp (made by a local bloke)...
I've put a small clip on fan at the back of the Supro in the hope it'll help cool it somewhat, but I'll look into getting it mounted separately.
Barring how warm it gets, it's a gd little amp.
Thanks for the lesson. I now understand why my amp would occasionally blow a fuse out of the blue for no apparent reason.
Ty for the info. As mentioned, I never thought about the difference. Ty for sharing.
Another excellent video. I’m learning as I try to watch your catalog of videos.
Thanks for sharing your knowledge and expertise.
Great video!
Great explanation well done
Great description mate, very informative... *runs off to check his amps..*
very well done. I ran over to the engineering mindset channel to try and figure out current without the plumbing
thank you for explaining this nice job
Your current waveform illustration is good and probably the best way to show how inrush current affects fuses. As you know, the inrush current is mostly due to charging of filter capacitors (plus some due to extra startup current through tube filaments). Your diagram is generally correct for amps with solid state rectifiers, except that the inrush current lasts for many more ac cycles. Note that there is no voltage surge since utility power is a constant ac voltage source.
Things are more complicated with tube rectifiers because the inrush current through the rectifier increases as the rectifier tube warms up, then decreases as the filter capacitors become charged.
The inrush current stresses not only the fuse, but of course also the power transformer and the rectifier. As you know, that is why it is not a good idea to replace filter capacitors with ones of larger capacitance, and why solid state rectifiers need to have a resistor (or inrush current limiter) ahead of the filter capacitors.
I didn’t mean that the mains voltage increased. But on the DC side a switch (like standby) introduces a voltage spike.
My wake up call was when one of my precious tube vintage 50's tube amp fried the trannies and saw wall voltage was at 130. Now always use an AmpRx Brown Box/Brownie to dial in AC (suggest something like this) to the AC level that the amp was designed for. Many of the older amps are marked 117vac max, so figures they run best at the designed power levels. Even seen new amps label 117v.
Good stuff!
I think your representation is good on paper, however I have an old school amp meter on my variac, and when I switch it on, you can see the meter bounce high then rapidly settle once the standby is switched to operate mode (in correctly running and typical situations). So, a traditional amp meter (a meter with a needle) will demonstrate it for you perfectly. Old style meters work better translating current in those kinds of situations. Mine goes to 5 amps, and I have my variac loaded with a 5 amp fast blo in it - so it works for most 100w or less tube amps. Solidstate amps can climb in amperage quite a bit, so larger amps, bass amps, power amps can overpower my smaller variac. I have a 10 amp variac too, but I don't have an amp meter wired into that one (not yet anyway). There are many reasons for a power fuse to blow, most often tubes, but can be transformers, shorted diodes, other shorts. Another indicator for a slow blow type is a T (for time delay) stamped on the fuse itself. HT fuses are usually fast blow.
Great video as always, keep up the great good work. The amp would obviously benefit from a “Quantum Science Audio Silver Extreme Level fuse” only $4500 per fuse🤣🤣🤣🤣🤣
Fuses don't fail - they give their life and protect ;-)
Here are a couple of technical reasons why a fuse might fail for what seems to be no particular reason: 1) power transformers will appear to be almost a dead short circuit before they are energized and build a magnetic field in and around the copper coils/windings and iron laminations (you can confirm this with an Ohmmeter connected to the power cord of your amp; the primary of the power transformer probably measures only a couple of ohms). 2) The electrolytic filter caps connected to the secondary of the power transformer also will appear to be almost a dead short if they are discharged (which is usually the case if the amp has been sitting around unused for a few hours or days). And 3) The heaters of all the tubes have an extremely low resistance when they're cold and draw a lot of current until they heat up, And because the heaters are all wired in parallel, the more tubes the amp has the lower the combined resistance of them all. When you turn the amp on you will draw a large amount of current for a few seconds as the filter caps charge and the tubes start to heat up (the resistance of the tube heaters increases enormously when they're warm to hot, and the filter caps no longer present a dead short circuit once they are charged).
The inductive nature of the power transformer not only acts almost as a dead short when you first energize it, drawing a large amount of current, but because it is building a magnetic field the voltage going into it at turn-on actually overshoots and goes higher than the incoming wall voltage! Visualize the 60 hz AC as having 120 peaks of full voltage per second, and 120 dead spots per second where the voltage is at zero. Depending where the cycle of the wall voltage is at when you flick the switch and turn the amp on, you will have either a lesser or a greater inductive surge as the power transformer inductance charges. If you could somehow turn the amp on only when the AC voltage is at one of those peak points (one of the 120 times per second that it reaches peak voltage), the inductive surge would be minimal, but if you randomly happened to turn it on just as the wall voltage is slightly above zero and heading to its full peak, you'll induce a huge inductive ringing and voltage overshoot into the transformer, and that's when current draw is the greatest.
All of the above surge-producing scenarios detailed above will tend to weaken a fuse over time, and of course invariably it will fail not when you're practicing but at a gig. Always carry fuses of the correct value and type with you to your gigs and practice jams, and don't buy cheap-ass, no name or possibly counterfeit fuses off of eBay, Amazon or Alibaba!
What are the top name brands you recommend, my first rodeo here…thx very much.
Imagine you have a bucket full of marbles and an empty bucket sitting on a table. The marbles represents electrons.
When the two buckets are on the table the potential to do work is zero or zero volts.
The bucket on the table represents the ground state.
Lift the marble bucket up, the potential rises.
Start to pour the marbles out. The marbles moving out of the bucket represent amperage, the number of electrons moving past a certain point during a period of time.
From that fixed height, pour a little faster. The amperage(intensity)has increased but the voltage(potential) has remained the same.
Lift the bucket higher, and return to the original rate of dropping marbles. The potential has gone up but the amperage has dropped.
You can now describe both properties of electron flow in one motion.
Introduce an interceptor bucket to demonstrate a lift ground or a voltage dropping circuit.
For current, use the same diagram but use a thicker line that would
indicate an increase in current.
I would be hesitant to plug in any electrical devices into a generator. Unless it was an inverter type.large enough to handle a bigger load than what's connected. That's just me..but if you gotta gig it,,ya takes your chances..great channel, certainly one of my favs.
Your voice is so relaxing. You could do those ASMR videos. :)
I liked your sketch. Electricity moves in sine waves like sound light and I think gravity (gravity might be all my SiFi books 🤓) does as well.
Hey Lyle, the sine wave representation of current is accurate, in that it is a time domain representation of the amount of electrons flowing through the circuit. I know you know all of this, but maybe some of your viewers will appreciate the background. If we look at the simple version of Ohm's law, Voltage is equal to Current multiplied by Resistance (or V=IR, and yes current is represented by an I because French), the sine wave representation makes sense. This is because (generally speaking) the resistance of the circuit does not change, so as the voltage rises and falls, the current has to rise and fall to "obey" Ohm's law. For a general example, since the resistance is constant we can pick any number we want, so lets say it is 1. Then we get Voltage=Current x 1, or simply Voltage=Current, so the graph of the two would be identical, hence a sine wave is correct for both. If the resistance is anything other than 1, the graph of the current would just have taller or smaller waves than the voltage.
Thanks Leigh. Great explanation. I knew that was the case here but expected to get pilloried for using such a simplified visual representation.
In working on amps I myself think of the circuits as being weights and the fuses/wires/traces as being the strings that hold the weights up.
For instance, take an amp with a 6L6 and two 12AX7s. For the heater supply, the “string” supporting all four tubes needs to be able to handle the full “weight” of 2.7A (all the tubes). But if the tubes are wired in a parallel sequence as usual, the wire “string” to the last 12AX7 only needs to support the “weight” of 300mA.
@@PsionicAudio looks like i was late to the party agreeing with your sketch
@@PsionicAudio Thanks Lyle, the weight analogy is interesting, I had never thought of it that way! Quick question for you, I am looking to build my first fuzz face (actually I plan on making a few for friends as well, maybe 10 total) and I'm wondering if you know of a good source for components. I read the mojo components articles on your web site and I have a Mouser cart filled up with most of the circuit components (although I am not sure which 22 uf capacitor to get for the fuzz control), but the 3PDT switches, enclosures, pots, and jacks seem quite over priced. Do you have any recomendations for a decent place to get lower quantities of those parts, and which ones are the most reliable? Thanks again for all your great videos!
Thank you very much for fuse explanation.
I think I heard your intestine gurgling @ 15:36,
my 79 Super Reverb that I just got about 1 month ago just blew a fuse, what are the basics to check first?
or do you recommend a video episode I missed… thx again 😊
What is the best way to get amps to you for repair?
Omg, you touched the tubes
The horror :)
Current would be out of phase with the voltage. If I dig out the clamp on Tektronix current probe for inductively measuring current, and I can finagle a fancy digital O Tek scope I can show the voltage and the current in two colors. If I get super lucky one of their scopes will actually do a 3D display of the voltage & the current, and it looks really cool. It's not $130,000 cool so I don't own that O scope.
Do you do amp repair apprenticeships?
I prefer short bat switches, specifically Carling brand, for power and standby. I just think they look cooler, and classier. Also there is less length sticking out to be hit, bumped, broken off....and whatever else can happen.
I' have my Shiva blowing the 1l2 amp fuse do you know what can be the problem?
Fast or slow blow fuses in a 65 super reverb reissue?
Was always curious about whether I should use slo-blow or fast blow fuses in my amps. Thanks for clarifying. That said, it sounds based on your discussion, as there are different ratings on slo-blow fuses (MTD vs ???); medium, slow or fast, I presume.
Water hammer is the best analogy may be?
But what does Fender recommend there? A slow blow or fast blow? And you illustration was good.
Most of the new stuff has it on the label by the fuse. My new princeton reverb clearly says 2 amp slo-blow
Would that be the same for amp boards on stereo amps, would slow blow be the better option?
Use the fuse size and speed directed by the manufacturer.
Any general difference between the glass tube slow blow fuses and ceramic slow blow fuses?
For our purposes, fusing audio amplifiers and guitar amplifiers, ceramic fuses probably aren't necessary or advantageous. Ceramic resistors are typically sandfilled and they are designed to be "explosion proof". If you have some kind of industrial piece of equipment that might accidentally get hit with a massive voltage or current surge, many times it's normal operating points, an ordinary glass fuse could not only explode but also cause vaporized metal to be deposited all around the inside of the device causing arcing and short circuits and further damage. Expensive, high quality test equipment ( such as a Fluke multimeter) will often use sandfilled fuses (often large, epoxy fiberglass fuses, not ceramic) for protection so that you don't spatter metal around the inside of the meter by connecting it to a high voltage while the meter is set in the low voltage range, or measuring voltage when its set for amperage, and so on.
The commonest place I see factory-installed ceramic fuses, fast or slowblow, in audio gear is in big power amps that put out several hundred watts or more, with fuse values ranging from 8 to 20 amps. Not really necessary in most guitar amps, that are typically fused at 3 amps or less. Perhaps a good idea if you gig a lot at outdoor shows that are run from a generator?
All that, with the addition that glass fuses can fail if they get too hot, no matter the actual current. That might be what happened to the first tube in this amp.
@@PsionicAudio , hmmm... I haven't heard this before. Are we referring to
glass fuses getting hot from internal heating, or from ambient heat inside the amp, or both? If anything I would expect that glass fuses would allow infrared radiation/ heat to escape just as heat radiates out from vacuum tubes (athough the glass would also let heat enter equally well); ceramic fuses would tend to trap and hold any internal heat generated due to resistance in the element, and adding sand inside the ceramic fuse as an Electrical insulator also means that it is a Thermal insulator. Now if you want to prevent ambient heat from entering the fuse, the reflective surface of the white ceramic is probably much better than glass for that purpose. This is an interesting discussion, or perhaps quandary. And by the way I have seen heat-stressed fuses become resistors that measure several several dozen ohms .
Personally I think most people would probably prefer the glass fuse because most of the time even a layman can tell at a glance if it is blown. Also you might see the fuse element to be sagging a little bit as if it has stretched and this too indicates it needs to be replaced. But as every technician knows , visual inspection of a glass fuse can fool you and sometimes they are bad even though they look OK. A ceramic fuse of course requires you to get out the multimeter.
Ive been using fast blow fuse as its much easier and cheaper to purchase(im from the Philippines), im using the correct fuse rating with respect to what the circuit calls for and so far i havent blown a fuse yet. Is it safe to say that i havent had a current/voltage swing thats too drastic thats enough to blow it yet?
It all depends on the amp. One amp might “need” a 1.1A fuse. Another might “need” a 1.85A fuse. Both amps will use the next standard rating up, so both amps will use 2A fuses.
The first amp asks less of that 2A fuse than the second amp.
Hope that makes sense.
Completely unrelated, but I figured I'd ask: I have a Monster Pro 7000 MK2 power conditioner in my studio. It has 2 Amp Slow Blow for audio and digital and a 10 Amp Slow Blow for video. Are these 250V or 125V. I can't find the information ANYWHERE online. Please help!
Most fuses are rated at 250v. It’s not like amperage as in you can put a higher rated voltage fuse in and be fine. The amperage is the important rating here
Really hot in Memphis can make a new yorker sterile
Why would anyone buy a fast blow fuse?
Sensitive circuits
There's no need to show the sine wave because the fuse reacts only to the RMS (equivalent DC) current anyway. A 12AX7 I just checked measures ~3.5 ohms cold resulting in 1.8 amps, six times the current cold, and it takes a few seconds to drop all the way down to its rated 0.3 amps. Meanwhile, the power supply capacitors look like a short until charged limited only by the minimal inductance of the transformer windings, which is an additional challenge with solid state rectifiers. The fuse time/current curves are available on line. (see www.mecampbell.com/media/pdf/ID-SPE-Bus_Ele_DS_2004_MDL_MDL-V.pdf) To the commenter using up-sized fast-blow, that's short circuit protection but no overload protection, which is hardly any protection. All you are doing is protecting the house fuse, not anything inside your amp. That amp could get hot enough to literally be in flames by the time the failure escalates to short circuit levels, typically because insulation melts. We engineers call this fuse coordination - the fuse time current curve must be matched as close as you can to the load's time current curve without crossing for optimum protection.
Do you have a better suggestion for visually representing current for musicians to understand?
PS musicians - I consider myself one. This is not about musicians being “dumb” - it’s about a specialized vocabulary.
@@PsionicAudio The only "water through a hose" analogy I can think of would be a hose with a weak point -- a bottle neck or a hernia -- that cuts out if the pressure exceeds the wall limits. Not sure that would really clarify much. As a side note, it's not easy to find a slow blow fuse at the local home despot or lowest, between what they stock (especially in the Amp range you might need) and inscrutable labels and codes.