what about amplifier where existing fuse it is 4A slow blow? Next value from SR it is about 5A. Do you recommend also greater value of 5A?Yes, based on a number of experiences that have been reported earlier in this thread that would seem to be a prudent thing to do. In my opinion, from a technical standpoint there is negligible risk in doing so. The only possible downside I can envision is that if an unrelated problem arises in the amp, and the amp is under warranty and the manufacturer becomes aware of the substitution, they could conceivably use the substitution as an excuse to not cover the cost of the repair. But even that seems very unlikely.
Good luck. Regards,
-- Al