Problems with blown fuses on Conrad CAV 50 ?

I am experiencing a recurring issue of the F1 fuse (4 amp, slow blow) blowing about once every three weeks.
I use the amp about 1 to 2 hours per day on average. During operation it works beautifully, but I am keeping Circuit City in business by buying their fuse inventory on a regular basis. I noticed that although the replacement fuse from Circuit City is of the correct rating, its design sports a droplet design (if there is such a qualifier) as opposed to the coiled wire design of the original fuse. Could that be the issue ? Where could I find such a fuse ?
Thank you in advance for any advice.

Souds like you have a bad tube. Mine usually blew when powering up the amp. Try retubing the unit and see if that solves the problem.

Blown fuses are very common in c-j gear when it's time to change the tubes. Just pick up a new set and you'll stop buying fuses. Happy listening!
Thank you a weak tube was indeed the root cause of the problem.