Which fuse ?

[koen]

My Mision Amps DIY 5E3 is completely dead (after sitting in the attic for several months). I suspect a blown fuse. I know from the schematics it should be 2A, but are there other specs I should look for when I go out to buy some?

- Koen.

[soundguruman]

My Mision Amps DIY 5E3 is completely dead (after sitting in the attic for several months). I suspect a blown fuse. I know from the schematics it should be 2A, but are there other specs I should look for when I go out to buy some?

- Koen.

I think it's 3AG, 250 volt, 2 amp, slow blow fuse, but you could ask Bruce at Mission Amps, to be sure.

[Bruce / Mission Amps]

Yes, 3AG @ 2 amps slo-blo or MDL.
Actually, a good running 5E3 won't blow a 1a slo-blo fuse either.... but a bad power tube or a short somewhere will blow 3 or 4 amp fuse.

Be careful though... sitting doing nothing for a few months... and then blowing a 2 amp fuse when firing it back up sounds suspicious.

[soundguruman]

That's a very good point, all too often ignored.
When your amp blows a fuse, you need to figure out what makes it blow.
Instead of just putting another one in, and blowing it again.
How many amps is a gum wrapper?

[koen]

I don't know if it was a blown fuse, that was just a guess. I haven't had the time yet to look at it again, hopefully more in the next couple of days.

Anything else I could check?

And I don't know the answer to soundguruman's question about the gumwrapper...

[Bruce / Mission Amps]

I don't know if it was a blown fuse, that was just a guess. I haven't had the time yet to look at it again, hopefully more in the next couple of days.

Anything else I could check?

And I don't know the answer to soundguruman's question about the gumwrapper...

In the old days it was common to find an amp with a blown fuse wrapped with the foil wrapper from a strip of gum... the foil bypasses the blown fuse.

At this point, and you guessing, I don't know that the fuse is blown... you could even have a bad outlet... or the amp wasn't plugged in all the way... etc.

Pull all the tubes out and put a new fuse in. Restart the amp with no tubes and see if it lights up.
If yes, put the rectifier tube in and see if it lights up or blows the fuse.
If OK, put the preamp tubes back in... if OK, put the power tubes back in.
If it blows the fuse during any of those steps then you have a little work to do trying to figure out what the load of that test would do to cause a current surge.

[soundguruman]

Relax, if you don't know about the gum wrapper, you can use a penny instead.

[koen]

A quick update.

I stopped by RadioShack on my way home yesterday and got 2A sloblo fuses. But they are too small and don't fit.... grrrr I hate that store. So until I have the correct fuses, I won't be able to do more testing. I'm hesitant to use a gumwrapper or penny to bypass the fuse

[Jazz P Bass]

Don't know why your are dissing Radio Shack.
You bought the incorrect fuse.
1 1/4 x 1/4 is pretty "standard" on tube amps.
2.0-Amp 250V 1¼x¼" Slow-Blow Fuse (4-Pack) - RadioShack.com
Although some amps require the smaller 5x20 mm (metric) fuses.

[koen]

Ok, I feel incredibly stupid. When I flipped the amp on, I flipped the standby switch instead of the power switch. No wonder it wouldn't turn on. That happens when you don't use it for 6 months...

At least I got a set of spare fuses now

[Gaz]

wow, that's pretty bad. a happy ending nonetheless.

[Bruce / Mission Amps]

Ha ha... I guess I should ink the chassis so it says On-Off and standby somewhere by the switches....