Fuse problem:cannot understand what i'm missing


Hello fellow Audiogoners.I need your help.
A year ago i replaced a stock fuse on my Krell SACD mk3 (slow blow 500mA 20 mm (small)) with Hi-Fi Tuning fuse.
I threw away that Krell fuse thinking that i can always buy one at Radio Shack.I did some changes in my system and decided to try how Krell would sound with a generic fuse through my system.I went to Radio Shack and bought a 4 pack of Slow Blow fuses (T 500mA 250V).They all burned down one by one as soon as turned the power switch on.Everything is OK when i put back Hi-Fi Tuning fuse with the same specs.The fuses that burned down were slow blow fuses,500mA .I cannot understand why they are failing but a Hi Fi Tuning fuse keeps working without a problem.Are there any other specs that i'm missing?Please,help me solve this dilemma.Thanks a lot!
overhang
The "T" instead of "SB" probably means "Time Delay".

The delay characteristic may be different from the fuse supplied by Krell.
I went through the same thing with Radio Shack "slow blow" fuses. They are not slow blow. The construction looks like regular fast blow fuses and "fast blow" they do!!

I ended up ordering from Mouser.