4010 Blowing HT fuse when I play

[musicchops]

JCM 800 blowing the HT fuse but only when I play music through it. I can leave it switched on all day and nothing will happen, but as soon as I play my guitar then 'CRACK' it blows with a black fuse as the result.
I have changed the O/P valves.
Any ideas?

 

[Trapland]

Make SURE you are using SLO-Blo fuses. If you are, then it’s probably power tubes.

 

[Jethro Rocker]

Make SURE you are using SLO-Blo fuses. If you are, then it’s probably power tubes.

He did change them but still makes sense to me. Perhaps just uisng fast blo fuses. Otherwise I am stumped

 

[6StringMoFo]

Just saying, we have a workbench channel.