AMP W/O A FUSE,,,,

[ksl]

Hi all~ This is an old Knight KM15/Y784, a    2-EL84 amp w/EZ81 rect., but it has no fuse. Nothing!!  Advisable to put one in immediately??, & how would I determine what amp fuse to use? And it would be an HKP model?
Pics attached, 
Thanks folks

[Grant Harding]

Are you doing modifications to these old things yourself? If so, your general lack of understanding seems extremely dangerous. This stuff is deadly and can set places on fire. 

Edit: This is more of a warning to anyone providing enabling advice. 

[ksl]

Thanks Grant,, I got this, & my 'real' tech has given me the 👌 on all of my 3-way cords, and this one seems pretty straight forward, other than the necessary addition of a fuse, and the path remains the same.        I don't perform anybody the other mods required, but the AC cord wiring, though dangerous, is, after a lengthy  cautionary education, rather straightforward. Agree? 

But seriously, thank you again for your continuing concern. 

Kenny

[daddymack]

late to the party, but I would never even plug in an amp that didn't have a fuse on the AC in line. Grant is correct, risk of fire, electrocution and damage to the amp is why amps have fuses.

Back in the late 1940s and into the late 1950s, these kinds of designs were on the market, because they were cheap and 'functional', but little consideration was given to end user safety..caveat emptor was the rule of the era.

The AC part of an amp is basic electrical stuff, like wiring a wall socket or a wall switch, except that what you plug into the socket or turn on with the switch should be UL approved. Looking at some of the projects you are working on, I shake my head all too frequently. There is a reason you are finding these old project amps ,and probably cheaply purchased, and that is they need to be upgraded on several levels.

Many years ago, when I was a computer system bench assembler/jr tech, I watched a coworker decide to cut the lead of a capacitor without discharging it first...his dykes missed me by an inch when they flew out of his hand. We picked him up off the floor, but he couldn't stand up, and we had to call an ambulance. He couldn't talk or control his muscles. He suffered mild but permanent brain damage, and lost dexterity in his right hand. Couldn't work on the bench, so we transferred him to the expediting department. He resigned shortly thereafter.

Sadly, Kenny, you remind me of his incident when I look at the things you are doing...

[ksl]

Again, thank you both for your relentless cautionary reminders about this topic. And again I will respond with that I know how discharge caps, and the only other thing I do is install 3 prong cords, and I have investigated it ad nauseam on multiple sites, shown them to my 'interior tech', and have displayed proper knowledge of the topic.  You were all correct, it's rather easy once you get the concept & schematic down. I don't mod amps, I'll change a bad resistor or cap, and fully understand the hazards, & take all the precautions. I don't even plug an amp in after I've converted the cord... my tech is ALWAYS the next stop.  ALWAYS ~

[daddymack]

Thanks Kenny...we do enjoy your forays...but we do worry...keep at it, carefully!

[ksl]

I got this, & only this!! I've had enough close encounters w/117 & 240v over my 40yrs+ career, and I know where the hazards lay....

Thanks again & never stop caring for others!! Both you guys!!

Kenny

[ksl]

So, how would one determine what value fuse to use? Someone on Ampgarage mentioned a 1a slo-blo, but you know I like to kill an ant with a hammer!!  Any thoughts, on the fuse that is? 🥴

[daddymack]

I might go with a 1.25 or 1.5 amp standard, maybe a slo-blo, it is okay in a tube amp, but for a SS amp it can allow more damage...

but I can't read that fuzzy schematic to see what the current draw would be.

[Idunno]

Looks to be 50 watts beneath the line chord plug under the transformer, making the running current just under 1/2 amp. Upping that 1-1/2 times puts inrush current at 0.750 amps. Sol-Blo fuses degrade. I prefer fast acting. Can experiment with lower rated fuses (0.50 amp, 250 Volt and lower) to see what the performance is but out of the gate I'd take an amp reading with a decent meter that stores peak inrush current as SOP and equip the unit accordingly with properly rated protection. If you're going first cabin there are re-settable fast-acting panel-mount push-button breakers available in that range going pretty cheap.

[Mikeo]

On 7/29/2020 at 2:34 PM, daddymack said:

late to the party, but I would never even plug in an amp that didn't have a fuse on the AC in line. Grant is correct, risk of fire, electrocution and damage to the amp is why amps have fuses.

Back in the late 1940s and into the late 1950s, these kinds of designs were on the market, because they were cheap and 'functional', but little consideration was given to end user safety..caveat emptor was the rule of the era.

The AC part of an amp is basic electrical stuff, like wiring a wall socket or a wall switch, except that what you plug into the socket or turn on with the switch should be UL approved. Looking at some of the projects you are working on, I shake my head all too frequently. There is a reason you are finding these old project amps ,and probably cheaply purchased, and that is they need to be upgraded on several levels.

Many years ago, when I was a computer system bench assembler/jr tech, I watched a coworker decide to cut the lead of a capacitor without discharging it first...his dykes missed me by an inch when they flew out of his hand. We picked him up off the floor, but he couldn't stand up, and we had to call an ambulance. He couldn't talk or control his muscles. He suffered mild but permanent brain damage, and lost dexterity in his right hand. Couldn't work on the bench, so we transferred him to the expediting department. He resigned shortly thereafter.

Sadly, Kenny, you remind me of his incident when I look at the things you are doing...

I was playing at a festival one day a long time ago, and the bone head electrician wired the stage for 240VAC, instead of the standard 12VAC. I didn't have my guitar plugged in, but when I turned on the amp and warm it up, it was dead as a  door nail.

I have no idea what else was fried that day.

The outside fuse doesn't do much until it does everything, like save your life. 

I thought they fried my amp, but they didn't. The outside fuse protected the amp too.

I ended up using another amp that day. I don't normal carry fuses, but probably should.

I have em in a bin of electronic stuff in my cellar.

 

 

 

 

[daddymack]

Fuses are a must for the 'any eventuality kit' for guitarists...along with duct tape, electrical tape, spare tubes, pens, wire strippers, wire cutters, scissors, spare cables for everything, spare batteries for clip on tuner, Phillips and straight blade screwdrivers in two sizes [or an electric on with backup battery], back up tuner, cana tuner fizz...and optionally, a 105mm Howitzer.