The weakest kink in your tube amps power supply... the fuse

Discussion in 'Glowing Bottle Tube Amp Forum' started by DrPepper, Apr 5, 2021.

  1. DrPepper

    DrPepper Friend of Leo's

    Age:
    62
    Posts:
    4,490
    Joined:
    Nov 24, 2017
    Location:
    Frying Pan
    Not upgrade as in up the amperage but, as in higher quality or unconventional materials...
     
  2. DrPepper

    DrPepper Friend of Leo's

    Age:
    62
    Posts:
    4,490
    Joined:
    Nov 24, 2017
    Location:
    Frying Pan
    Well at least reading the varied opinions of others is entertaining. I can't practice 24/7... Hey, what are you doing here? :)
     
    getbent likes this.
  3. DrPepper

    DrPepper Friend of Leo's

    Age:
    62
    Posts:
    4,490
    Joined:
    Nov 24, 2017
    Location:
    Frying Pan
    Thank you... Well said and understood...
     
    archetype likes this.
  4. telemnemonics

    telemnemonics Telefied Ad Free Member

    Age:
    61
    Posts:
    28,409
    Joined:
    Mar 2, 2010
    Location:
    Maine
    Wow, you unlearn something every day!
     
    Oldsmobum likes this.
  5. telemnemonics

    telemnemonics Telefied Ad Free Member

    Age:
    61
    Posts:
    28,409
    Joined:
    Mar 2, 2010
    Location:
    Maine
    Wait, the idea here is that the weakest link is the consumer?
    (kink?)

    If consumer society blew its collective fuse, all corporate activity would go dark, so there's that.
    Right now consumers are straining the grid with rabid consumption, and that sort of thing does historically lead to blown fuses, which is better than blowing transformers or melting the whole mess down.
     
  6. alnico357

    alnico357 Tele-Afflicted

    Posts:
    1,994
    Joined:
    Jun 2, 2015
    Location:
    Arkansas
    I always use the fuse type supplied. Once a 6L6 shorted and took out a 5 watt power resistor, so fuses do not always work!

    That was maybe 10 years ago. I have blown perhaps 3 fuses in 55 years.

    IMHO, using a different fuse type is a dumbgrade.
     
  7. King Fan

    King Fan Poster Extraordinaire Ad Free Member

    Posts:
    6,659
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Staying with the OP's question, about 'nicer' materials not increased amperage, I still don't get how folks might say the fuse/holder/switch would be a 'weak link' in an amp. Weak in what way?

    Hmm, maybe we could replace the fuse holder with a big MM PT (not remotely the same function, of course, but nice and spendy), replace the fuse with a big chunk of Monster cable, and replace the switch with one of those things Dr. Frankenstein uses? Wire it all to a lightning rod and wait for thunder?

    Weak link... weak link... (wanders off, shaking head).
     
    Oldsmobum and DrPepper like this.
  8. fjblair

    fjblair Tele-Holic

    Posts:
    984
    Joined:
    Dec 29, 2010
    Location:
    NC High Country
    This thread reminds me of the times when I was young and had no spare fuses, so we used aluminum foil.
     
  9. scooteraz

    scooteraz Friend of Leo's

    Posts:
    3,609
    Joined:
    Apr 17, 2007
    Location:
    Peoria, AZ
    The conventional fusible link is pretty amazing material/manufacturing to begin with. Not sure what would be accomplished with “better” materials. Exactly what performance parameter do you want to change? If you can think of none, then there is no improvement to be made with different materials.

    So, if you go here, you can see the specifications for Littlefuse 3AG slow blow fuses. The first thing to remember is that the fuse will be rated so that standard expected current draw will be 80% of the fuse rating. So, that 3 Amp fuse I used as an earlier example is designed to protect a circuit with up to 2.4 amps of normal current draw. Still, when you look at the specs, the fuse is specified to take at least 4 hours before it blows at 3 amps. If it never blows at exactly 3 amps, it still meets spec. At 135% of rating or at 4.05 amps, it is to last one hour, maximum. At 200% of rated load, it is to last at least 5 seconds, but blow before 30 seconds has expired. Think about that for a second, the fuse MUST give 5 seconds before blowing, but not more than 30 seconds at 6 amps (for the 3 amp rating). It is also expected to interrupt 100 amps at 250 Vac or 10,000 amps at 125 Vac. In other words, there is no capability even at those high amperage to create a self sustaining arc. When you look at the curves, you can see our little 3 amp buddy lasts an average of .01 seconds at 90 amps, and about a second at 15 amps. That is all pretty impressive to me.

    https://www.littelfuse.com/~/media/...ses/littelfuse_fuse_313_315_datasheet.pdf.pdf

    Fuses are actually pretty fascinating little devices. But if you really want to “upgrade”, I guess you could find an appropriate resettable breaker. The push to reset devices are used pretty often on electronics. Something like this TE Connectivity Potter & Brumfield W28 would be closest in form factor to the fuse on your amp.

    https://www.te.com/usa-en/product-3-1393250-4.datasheet.pdf

    The other option is a W58 style, sort of the thing used on light aircraft.

    https://www.te.com/commerce/DocumentDelivery/DDEController?Action=showdoc&DocId=Data+Sheet1308242_W580510pdfEnglishENG_DS_1308242_W58_0510.pdf1-1393249-4
     
    Last edited: Apr 5, 2021
    archetype likes this.
  10. scooteraz

    scooteraz Friend of Leo's

    Posts:
    3,609
    Joined:
    Apr 17, 2007
    Location:
    Peoria, AZ

    I will grant there are better and worse fuse holders. The worse ones will break with fewer fuse replacement cycles/overheating cycles than the good ones.
     
  11. dickey

    dickey Friend of Leo's

    Posts:
    2,432
    Joined:
    Jan 2, 2010
    Location:
    Florida
    I'll do you one better...I would bet that blindfolded, no one can tell the difference between tube brands,strings, or speakers.
     
    Paul G. and Oldsmobum like this.
  12. DrPepper

    DrPepper Friend of Leo's

    Age:
    62
    Posts:
    4,490
    Joined:
    Nov 24, 2017
    Location:
    Frying Pan
    Well, I think I will implement some different switching/fuse arranement in my 5E3 build. No, not the audiophile stuff but I will get some ceramic fuses (I am going to fuse both legs of the mains)... pics coming
     
  13. Bob Arbogast

    Bob Arbogast Tele-Afflicted Silver Supporter

    Posts:
    1,783
    Joined:
    Mar 16, 2003
    Location:
    Lowell, Michigan USA
    My habit is to under-fuse my amps for extra protection. If the amp calls for a 2A slow-blow fuse, I usually install a 1.5A.

    Also, when a tweed chassis is screen-printed with the original fuse value, I definitely under-fuse. *I'm not sure, but I think* the fuses in 50s amps were not slow-blow. So if the screen-printing says 3A, it may mean "3A fast-blow." Someone with more knowledge can confirm or correct this.
     
    AlbertaGriff likes this.
  14. LOSTVENTURE

    LOSTVENTURE Friend of Leo's

    Posts:
    2,017
    Joined:
    Feb 13, 2007
    Location:
    Charlotte, NC
    The fuse is not the weak link, it's the protective link.
     
  15. fattybrisket

    fattybrisket Tele-Meister

    Posts:
    222
    Joined:
    Apr 1, 2008
    Location:
    Santa Cruz Mountains, CA
    Not to hijack the thread but I am thinking of changing from a cream-colored wall socket cover to a brown one. I want to sound less like Clapton and more like Van Halen.
     
    Paul G. and Oldsmobum like this.
  16. Blrfl

    Blrfl Tele-Afflicted

    Posts:
    1,394
    Joined:
    May 3, 2018
    Location:
    Northern Virginia
    If the part failed without starting a fire, the fuse didn't need to be involved. 5 watts isn't much more energy than the night light in your bathroom dissipates.
     
  17. Blue Bill

    Blue Bill Poster Extraordinaire Ad Free Member

    Posts:
    8,702
    Joined:
    Feb 15, 2014
    Location:
    Maine
    I am curious, so I did the math: The question seems to be, how can that little tiny wire inside a fuse, properly pass all the current needed, at 120 Volts AC, to properly power a fire-breathing tube amplifier, right? The resistance in that little biddy wire must bottle-neck the flow of electricity, therefore it affects the function of the amp, right?

    The resistance of a wire is calculated by the equation R=p x L / A, Resistance in Ohms = Resistivity of the conductor in Ohm-Meters, times the Length of the wire, in Meters, divided by the cross-sectional Area of the wire, in square Meters.

    Resistivity of Aluminum is 2.6 x 10^-8 Ohm-Meters
    Resistivity of Copper is 1.7 x 10^-8 Ohm-Meters

    I don't know what metal is used in fuses, most metals are between 1 and 3 x 10^-8 Ohm-Meters, so let's guess the fuse wire has a resistivity of 2 x 10^-8 Ohm-Meters, for ease of calculation.

    Most fuses are about 1-1/4 inches long , so L = 0.03175 Meters

    A, is the cross-sectional area: I looked up fuse wire gauges; it looks like a 2 Amp fuse will need around a 22 ga wire, which is 0.3255 mm squared, or 3.255x10^-7 Meters squared.

    Resistance = (2x10^-8 Ohm-Meters) x (0.03175 Meters) / (3.255x10^-7) = 1.95 x 10^-3 in Ohms

    So a fuse has a resistance of somewhere around 0.002 Ohms. Hmmm, that means about 500 fuses, wired end-to-end, would have a resistance of one Ohm.

    What I get out of this is that since resistance of a wire is directly proportional to it's length, the shortness of the fuse wire introduces only a teeny-weenie resistance into the circuit, a virtual short-circuit. To me this is why a fuse has no significant affect on the circuit.

    Feel free to double-check my math, or shoot holes in my procedure.
     
  18. scooteraz

    scooteraz Friend of Leo's

    Posts:
    3,609
    Joined:
    Apr 17, 2007
    Location:
    Peoria, AZ

    Not sure about your wire size; 22 ga is good for something like 7 amps in chassis wiring. So, obviously it wouldn’t get hot enough to melt at 2 amps, even after an hour. However, your larger point is correct. The fuses have a resistance that is negligible in most cases.
     
    Asmith likes this.
  19. gusfinley

    gusfinley Tele-Afflicted

    Posts:
    1,434
    Joined:
    Jun 11, 2014
    Location:
    SLC, UT
    Hmmm.... So If you replace the fuse with a 3AG light bulb, you have a built-in limiter?
     
  20. Blue Bill

    Blue Bill Poster Extraordinaire Ad Free Member

    Posts:
    8,702
    Joined:
    Feb 15, 2014
    Location:
    Maine

    Hi Scooter, you may be correct. 25 ga wire is 30% smaller in diameter, and only half the cross-sectional area of 22 ga. so, the R calculation doubles to around 0.004 Ohms, still tiny.

    Here's what I looked up: https://www.oznium.com/blog/how-to-determine-the-fuse-wire-size-for-your-project/

    Screen shot:

    Screen Shot 2021-04-06 at 12.33.36 AM.png

    https://www.rapidtables.com/calc/wire/wire-gauge-chart.html

    screen shot:

    Screen Shot 2021-04-06 at 12.39.58 AM.png

    Another rough calculation: (1000 feet x 12 inches/foot = 12000 inches)

    (1.25 inches / 12000 inches) x (268.46 Ohms/Kft) = 1.04x10^-4 or .0001 Ohms, much smaller than my previous equation calc. Hmmm. I used carbon steel for this example which has about 8 times the resistance of copper, per foot. Hmmm.
     
    Last edited: Apr 6, 2021
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.