[Jerome W]

Hi JJ. Sorry to read this.
Do not take the decision to part from them just because of a fuse after some tube failures. I had one of the fuse of one of my CCQ blow away 2 months ago. Fuses are here to blow and that is good when they do.
Many things can happen when you power on a tube amplifier.
Unfortunately our domestic AC current can be of very poor quality during very short time. You want the fuse to blow when this happens ! Do not blame your amp. Blame your AC company provider !

But I would still test your the tubes just to be sure. It could be a tube getting bad. Moreover, did you recheck the bias about 100 hours after changing the last 300B's ? If the bias changed and was not adjusted, you can have there an other reason for a fuse blow.

As many said before, tubes are by nature unreliable. They compensate this by sound quality. There is a price to pay for every thing in this world.

There cannot be any "design flaw" in your amps. Because they were made by one of the best tube circuit design experts in the world. Would you question a simple multiplication made by a Fields Medal mathematician ? Are you kidding ??

Now, the most reliable tubes on earth have your first name on them: JJ.
Please try them if it appears again that one GL is faulty. And be sure to set the bias correctly and recheck it after 50 / 100 hours.
Good luck buddy !