K-4040: two 2.5A (at 230v AC use) fuses blown within 2 hrs

On switching on my K-4040, the fuse F1, 2.5A, was blown during switching from pre heating to operate. After replacing it by a new 2.5A fuse, it all woked fine and I did use the amp for approx 2 hrs and enjoyed the performance quite a lot. But when I switched off the amp, the second 2.5A fuse blew (with a rather impressive flash)

The amp has worked fine during bias adjusting and some simple tests before, so I think this is very strange.

When I insert a 5A fuse , LD-2 at the front turns red, but LD-1 remains off (front switch in OFF position) As I do not remember if LD-1 should be on as well ( based on the diagram it wouldn’t) but I thought it was on during previous attempts, I am not sure were to start looking.

Any suggestion?

Best regards,

Mark

All current versions of the amp are equipped with 5A fuses, as 2.5A is at the limit.

Okay, noted and thanks!

Best regards,

Mark