Lone Star Special blew power fuse using effects loop

[breakout8]

My Lone Star Special blew its power fuse in a big way (blackened inside) the first time I used it with a Boss GT5 in the loop after about 5 minutes of operation. I have since replaced the fuse and it works fine without engaging the loop and I'm now more than a bit hesitant to try it again. The manual suggests most fuse failures are caused by shorting power tubes but as it has functioned without issue since fuse replacement could this relate to a tube in the loop being the problem?
If anybody's encountered this problem before I'd really appreciate any ideas as to the likely cause before I take it to my amp tech.

 

[twally]

Even though it powered back up it could still be a bad power tube. Look at the tubes while the amp is powered up and strumming on your guitar. Do you notice any arc's? Take a pencil and tap on the power tubes. Do you hear any static or other strange noises? If so, you have a bad power tube.

TW

 

[ricardo loma vista]

Another common cause of fuses blowing in the LSS is a bad rectifier tube. My last one failed exactly that way. I would replace the fuse and it would blow again within 5-30 minutes. Your LSS should still be under warranty so the first thing to do is call tech support. An new 5Y3 should fix the problem.

It's possible that that a shorted cable or a short in the Boss blew the fuse, but it seems unlikely.

If you want to experiment, leave the amp on for a couple of hours, with nothing in the FX loop and see if your fuse blows again. If you've got a bad rectifier, it will fail again. In the meantime, check your cables, and verify whether the Boss unit is working.

If your rectifier tube fails during a gig, you can run the amp in 30W mode with the rectifier tube removed. The rectifier tube is only used in 15w and 5W mode, but if you don't remove it, is still in the circuit and can still blow the fuse.