Fuse Blowing on Superamp AE 25

2 caveats w/new tubes, 1)be sure to turn bias screws back (counter clockwise) to minimum before you insert new tubes and turn on. 2) Although it was not a problem for me with my Cary amps, it is not unusual for a power tube loss to be accommodated by a blown out resistor in the bias curcuit. You should note this when you bias new tubes if it exists.

Hope that solves your problem.

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.

If your 1/2A fuses are good; it's probably not an output tube problem. Hopefully, just a weakened fuse and not something power supply related.