Amp Fuse

[kolaking]

Turned on amp and nothing, put in the spare that came with it and blew it in 1 second. Can't find the exact replacement. So will a 1.6a 250v work safely instead of the 1.6a 100-117v in my Egnater. If I can only get that voltage fuse should I maybe go up to a 2a fuse?

[Steve Conner]

If it blew two fuses in a row, it's a safe bet that there's a serious internal fault. If you replace the fuse, it'll just blow again. If you substitute a bigger one, you'll just burn out some bigger and more expensive parts. If it's a tube amp, you can try removing the power tubes to see if any are shorted. If it's solid state, I suggest you take it to a repair shop.

The voltage rating on the fuse is just an advisory as to how much voltage it can safely withstand. You can replace a 117V rated one with a 250V rated one. But if you took a 117V fuse and used it in a 250V line, it might arc and explode instead of breaking the circuit cleanly.

[kolaking]

Yeah, I've had some hum when turning the tube selector to the EL84 so I''ll try checking them. The only thing different I did before turning it on this morning was try to plug some pedals thru the effect loop of the amp. Think that could have done something?

[kolaking]

Checked both the 6v6 and El84...Still blew the fuses. Guess I'll have to pull it from the chaises and start checking discrete components. Learning Time!!

[Steve Conner]

Nah, you shouldn't be able to kill an amp by plugging pedals into it.

I would spout a bunch of advice right now about PTs, filter caps and rectifier bridges, but I have no idea what your skill level is. We get plenty of people joining here who know absolutely nothing about electronics but want to try to repair their gear anyway. It rarely works out well.

[kolaking]

Go ahead, I know complete theory just never attempted applying it to Amps...It would be helpful to learn as this is the second amp that's crapped out not long after purchase. I know that I really need to get and o-scope, sig. gen., etc to properly repair, but I'm willing to put the money I spent on learning the theory to use.

[Alex R]

OK try replacing the fuse and pulling out the tubes before turning it on. If the fuse doesn't blow you have a shorted tube. Don't leave it on too long like that as the HT voltage rises a little and may exceed max volts on something or other. The old lightbulb in the power line idea is a great help with shorts.

[pdf64]

For 'light bulb limiter' see The Amp Garage :: View topic - TAG Light Bulb Current Limiter for some ways to implement one.
Pete

[kolaking]

Removed all tubes and still blows.?

[52 Bill]

Removed all tubes and still blows.?

Shorted power supply diode would be the next thing to check for.

[R.G.]

Go ahead, I know complete theory just never attempted applying it to Amps.

I like the quote from Yogi Berra. "In theory, there's no difference between theory and practice. In practice, there is."

The things that will keep you from painful and possibly fatal shocks when messing around in a live tube amp chassis are not taught in theory classes. Find a friend (or go make a new one) that has some experience with live high voltage chassis testing practice, or don't try it. Seriously, you can get dead.

..It would be helpful to learn as this is the second amp that's crapped out not long after purchase. I know that I really need to get and o-scope, sig. gen., etc to properly repair, but I'm willing to put the money I spent on learning the theory to use.

Then also spend some time learning how to do it so you're not at risk, and don't leave "fixes" that put you or others at risk, perhaps years later.

It would be much more useful to learn to make a light bulb limiter to use with a multimeter before buying an o'scope or signal generator. This also needs some practical high voltage wiring experience to make, but is much, much cheaper than formal test gear. Here's another link to the principles of the many-decades-old light bulb limiter.

[R.G.]

I forgot - never, never, ever replace the right sized fuse with a bigger one. That's one invitation to more damage or starting a fire. The AC primary fuse is there for two purposes: (1) to prevent a fault from starting a fire and (2) to prevent internal shorts to the chassis from being an electrocution hazard. They are not there to protect the internals from damage, although they may incidentally do that sometimes. But that's not their primary purpose.

[olddawg]

Is this an Egnater Rebel? This is a rather complex amp to work on for your first experience with the blended output. I would recommend taking it to an authorized servicer. Maybe try working on a simpler amp or build a small kit amp. Nevertheless, do you know how to safely static test the diodes in the rectifier circuit? Do you know how to safely float the secondaries on the PT? Something is drawing excessive current. It's a matter of finding what and where. If it is blowing fuses with all of the tubes out I would be suspecting the rectifier or the PT.

[bob p]

Just in case nobody's ever told you this rule before: when you're working on a tube amp, use one hand only and keep the other hand in your back pocket at all times.

[Leo_Gnardo]

There's been a minor rash of dodgy toroidal power transformers @ Egnater. Of course they don't much want to talk about it BUT if you find yours is bad they'll sell you a new one or maybe just send one if the amp's under warranty.

Detach all your PT secondaries & fire up (with light bulb current limiter on your AC supply line for extra credit). If you light up bright or pop a fuse, you know where the problem is.