Anfontan
Banned by eurt
apl said:
A fuse will typically blow to stop something from starting a FIRE!!! APL is correct, get it repaired as soon as possible!!
A fuse will typically blow to stop something from starting a FIRE!!! APL is correct, get it repaired as soon as possible!!
G
ggunn
Crystal Flavolian
FALKEN said:
Like others have said, the fuse is blowing to prevent something more expensive and/or more dangerous from blowing. If the fuse you removed was a much higher amperage rating than is called for, then the damage may already be done. Your amp needs to see the doctor.
One caveat: if you are replacing a slo-blo fuse with a fast fuse of the same rating, then that itself could be the problem. Slo-blo fuses can pass momentary current spikes much higher than their current rating without opening up, and when you power an amp up it draws a lot of current right at first, charging up all those capacitors and such. This is normal and should not result in a blown fuse; it's when the amp draws a lot of steady state current that the fuse needs to interrupt the power to keep the amp from damaging itself.
Anyway, if you are putting in a slo-blo fuse of the correct rating and it is blowing immediately, stop messing with the amp and take it in to be looked at.
M
mixsit
Well-known member
Generally, assuming it's a glass case, you can see how a slow blow has the filament wrapped around a core where a fast fuse is just a similar size wire. They would both heat at the same power but the core acts like a heat sync -slows it down.
It's amazing the shit ya pick up along the way eh?
Not that it makes much difference at this point, but what was the rating on the first fuse?
It's amazing the shit ya pick up along the way eh?
Not that it makes much difference at this point, but what was the rating on the first fuse?
FALKEN
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mixsit said:Generally, assuming it's a glass case, you can see how a slow blow has the filament wrapped around a core where a fast fuse is just a similar size wire. They would both heat at the same power but the core acts like a heat sync -slows it down.
It's amazing the shit ya pick up along the way eh?
Not that it makes much difference at this point, but what was the rating on the first fuse?
yeah "filament wrapped around a core"..thats what I thought I was looking for, but the ones at radio shack were the same as the fast acting (thin) but with a bead in the center. I was thinking that might be the problem. I looked for the old fuse but all I could find was an burnt 500mA which can't be right; I think that was from another amp.
D
dementedchord
Psychotic State alumni ch
pull the output tubes.... replace the fuse if it blows you've got either bad filtercaps or diode bridge is blown... if it doesnt blow when tubes are pulled then replace and rebias the tubes....
FALKEN
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FALKEN
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well, I pulled the piece of plastic out; plugged in the amp, and blew another fuse.
Anfontan
Banned by eurt
FALKEN said:
Take the advice in posts 19, 21, and 22 - take it to a repair shop-pronto!
D
dementedchord
Psychotic State alumni ch
the part that came loose is just to keep you from misaligning the pins... as to the fuse... you have a major short there somewhere... either the rectifier is bad..(is it a tube as well?) or the filter caps are roached.... sounds like it's time to see a doctor.... does it smell real bad (probably not or you woulda said something) if so it could also be a tranny...
M
MCI2424
New member
FALKEN said:
FUSE CHARACTERISTICS: The characteristic of a fuse
design refers to how rapidly the fuse responds to various
current overloads. Fuse characteristics can be classified
into three general categories: very fast-acting, fast-acting,
or Slo-Blo Fuse. The distinguishing feature of Slo-Blo fuses
is that these fuses have additional thermal inertia designed
to tolerate normal initial or start-up overload pulses.
"Standard" fuses will normally blow instantly if presented with initial current spikes greater than it can handle. The application dictates which design is best. If the wrong fuse is installed, you can have it blow on power up everytime OR really fry the unit good. Make sure you use the right fuse to avoid these problems.
T
timthetortoise
MADE OF SANDALWOOD
For curiosity's sake, are those tubes JJs or GTs? Only reason I ask is because on every set of JJs I've gotten, the alignment key has broken off on at least one of the tubes. For no good reason too! Just barely pushing down and turning a slight bit to find the slot. LAME, I TELL YOU!
But anyway, follow the advice of these guys. Take it to a tech. I've only had one experience with an amp blowing a fuse and it was because of a bad transistor that was overloading the tubes, which would have eventually led to the tubes' and output tranny's demise.
But anyway, follow the advice of these guys. Take it to a tech. I've only had one experience with an amp blowing a fuse and it was because of a bad transistor that was overloading the tubes, which would have eventually led to the tubes' and output tranny's demise.
FALKEN
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I don't think they're JJs or Groove tubes. I bought the amp on ebay about a year ago and the guy had some serious high end tubes in it. I replaced the preamp tubes because its sort of a 50 watt plexi amp and the high end tubes just didn't sound right in it. When I pulled the power tubes I think theyre some german something or other...they weren't labeled as EL34s either. Unfortunately I accidently smashed them this morning.... Anywayz I included some new Sveltanas with the amp when I took it in today.
I could only hope its a transistor and not the transformer!
I could only hope its a transistor and not the transformer!
Zaphod B
Raccoons-Be-Gone, Inc.
Falken, when you replace the fuse, make sure the AC power cord is disconnected - otherwise the fuse will blow instantly.
M
MCI2424
New member
FALKEN said:
The last Marshall amp I fixed with a blowing fuse turned out to be the output transformer (to the speaker). The tranny was shorted. You could check out the impedance (resistance) across the transformer windings. Unsolder the tranasormer connections (in pairs) noting where they went and measure across them with an Ohmeter. You will find the shorted pair (input or output) in no time (if this is indeed the problem).
Good Luck.
G
ggunn
Crystal Flavolian
Zaphod B said:
??? I have never had that happen, and I have replaced fuses without disconnecting the amp many times. It's a good idea for the power switch to be off, otherwise you can get a nasty shock if you aren't careful, and a fuse that isn't a slo-blo would probably blow immediately if you put it in with the power switch on, otherwise I don't know how what you say could happen. With the amp plugged in and the power switch off, the only current path is to the neutral leg.
Zaphod B
Raccoons-Be-Gone, Inc.
It has happened to me with my old Matamp tube amp, every time I forgot to unplug the power cord.ggunn said:
Beats me as to why, but it's true!
(As they say, your mileage may vary.)
D
dementedchord
Psychotic State alumni ch
timthetortoise said:
WTF kinda amp was that??? the only tube transistor amps i've ever worked on used tubes in the front and solidstate out puts never the other way around.... and if you did build an amp like that i cant think of a way to overload the tubes to the popint of distroying an output tranny...
blowing output trannies is very rare IME (18yrs as a tech) in all that time i only replaced one on a guitar amp... i did replace plenty on old hammond pr40 tone cabs though... but they were all like 50 yrs old... if your blowing primary fuses and it aint the tubes 1st prize goes to diodes...2nd prize goes to filtercaps... and there's no reason to have to desolder the output tranny to check it ... just pull the tubes and it's out of the circuit for all intents and purposes...
G
ggunn
Crystal Flavolian
dementedchord said:
They are real easy to blow if you run a tube amp BTTW with no speaker attached. Been there, done that, paid through the nose. ;^)
D
dementedchord
Psychotic State alumni ch
ggunn said:
sorry i guess the guy's i've worked for were smart enough not to do this....
antispatula
Active member
dementedchord said:
I used to own a Peavy Duece, and it had a solid state preamp stage and 6l6's as the output. I thought that was the normal thing to do when it came to hybrids?
