(relative) Newbie Q: Amp is dead / no symptoms. Thoughts?

[Musicalbox23]

Hi all,

Just joined, but think I'm really going to get a lot out of this forum, really good stuff here. While I'd like to eventually build my own amp, first things first, I've got a Framus Dragon amp that just shut down at a gig and won't come back. No lights, no power, no sound. Fuse looks good, tubes checked out, transformer doesn't "look" blown and I don't recall the acrid smell that I've experienced in the past when I've been around transformers that have fried. I've tried new pre amp tubes but don't have local access to EL34's so I haven't tried replacing them yet. before I make a 100 mile round trip, does anybody have any other thoughts / suggestion on what to try?

Thanks!

Mark

p.s. I just did the "wrap the fuse in tin foil" trick too. Nothing. Grrrr....

[pecorporation]

One possibility is that there is a loose wire or solder error between the AC line cord and the fuse holder or power transformer wires. A second possibility is that there is an open primary coil on the power transformer possibly caused by an open internal thermal fuse in the transformer. You'll need to isolate the transformer leads from the AC line and take an impedance reading on the leads looking for 1 to 3 ohms which is normal, no reading indicates an open primary.

[Bruce / Mission Amps]

No idea on this one but, every once in a while I'll run into a chassis where there is two fuses in series, one is an internally mounted fuse that has a current rating a little higher then the one on the outside of the chassis... that way the external one blows first but if there is a big current surge, the internal one is blown too... how that happens is a mystery unless the outside one is a medium delay and the internal is not.
Other then that you have a bad power cord, hidden fuse in a fused IEC plug socket, bad on-off switch or as previously mentioned a fuse link inside the wrappings of the power tranny... which, regardless of what you might read here or elsewhere on the NET, a real stinker to fix so you'll most likely be replacing the power transformer if that's the case.

[Steve Conner]

No idea on this one but, every once in a while I'll run into a chassis where there is two fuses in series

Maybe that's to stop the usual expensive trail of destruction caused by the "wrap the fuse in silver foil trick".

Don't do it folks.

[Enzo]

Ampeg did that a lot - fuse holder on the outside rear panel, and inside another fuse in series, a pigtail fuse hardwired and rated about an amp higher than the fuse holder fuse. And that was precisely what it was for, gave the amp some protection when the proper fuse was replaced with a 30A fuse from the car.

Furst, the fuses. Don't look at them, pull them and test them with a meter. You cannot tell for sure a fuse is good by looking.

Pull the power cord from the wall outlet. Turn the amp p[ower switch to ON, make sure3 a good fuse is in the holder. Now look at your power cord plug. Two flat blades plus the ground prong. Use your ohm meter and measure resistance between the two flat prongs. You should see a relatively low resistance - something between maybe 5 ohms and 100 ohms. If you get such a reading, flip the power switich off and try again. Now the reading should be open. Open meaning reads the same as if the meter probes are not touching anything.

If the reading is open, no matter what, then we are not getting powr to the amp. At that point, we have to determine if the open is the transformer itself, or the power cord, or the switch ior fuseholder, or the amp's internal power wiring.

[Albert Kreuzer]

If the reading is open, no matter what, then we are not getting powr to the amp. At that point, we have to determine if the open is the transformer itself, or the power cord, or the switch ior fuseholder, or the amp's internal power wiring.

Or a defective voltage selector (if the amp has one).
Thought I'd mention it because I had one in the shop this week.

[Enzo]

Thanks Albert. yes, my list of things was not meant to be exhaustive. SOme amps have inrush limiters, and I am sure other things.

[pecorporation]

Gremlins?