Fuse Blowing on Superamp AE 25


Hello!
My AE 25 suddenly blew the main AC (2 amp sloblo) fuse. I took off the bottom cover and can find nothing that looks like a problem - no swollen components, no melting anywhere, etc.
Has anyone else experienced this? I am waiting for mail-order fuses now, and will put in a new one and try it, but it will be two weeks before they arrive. Meanwhile, I'm wondering if this is a common problem - maybe an AC spike that did it if the normal operating current is close to 2 amps? Any experience with this out there?
aatos

Showing 4 responses by aatos

Thanks for the idea. I will pull out all tubes before I put in the new fuse, then insert one at a time. Would that cause a problem?

No radioshack around here. No one I have shown the fuse to has ever seen one. Not an audiophile town.
I will still be waiting for fuses for a while, but I have checked all tubes with an ohm meter, and checked to fuses on the current source tubes. Nothing unusual. of course, it may be that the low voltage of the ohm meter may show nothing that occurs at high voltage. Still, at only a few hundred volts, there wouldn't be any significant dielectric breakdown, I would think. Am I wrong?
Thanks for all the input. I have spent some more time reading and measuring. First, the Superamp does not have any bias adjustment - it is auto-biased - so I don't have to worry about that. Second, I checked the resistors in each bias circuit, and all are reading within a few percent of their stated values. Finally, and I don't know how this fits in, the Superamp has a 1/2 amp fuse at the bottom of the bias circuits (between the resistors and ground) and that fuse is intact. Nevertheless, I have just ordered a new set of power tubes, EL-34's, which the Superamp will take with no adjustments required (using KT-88's now) and when the bits arrive (fuses, and tubes), I'll try them out. Hopefully my problem will be solved.
Yes! The power supply is essentially a single transformer with a centre tap and two output windings. If that has gone it will be a bugger to replace. There are two chokes, so I will check their resistance now.