[Jukebox-list] Re: 780 amp blows fuse

On 6/21/25 16:40, ascott822--- via Jukebox-list wrote:

I’m still trying to trace down the issue.  Box was playing fine a month ago.  Recently it blows amp fuse as record comes up. In trial and error tests I have found that it doesn’t blow with speaker unplugged.  Suggestions. Thank you, Allen

On these amplifiers the center tap of the power transformer is typically grounded through a jumper on the speaker plug, so disconnecting the speaker kills the high voltage. It's not the speaker itself that's the problem. It's that the plug is wired to shut down the amplifier unless it's plugged in.

I'd plug the speaker back in and pull the 5U4. See if the fuse holds. If so, plug the 5U4 back in, pull the 6L6s and see if it holds.