Hope this is the right forum to post in. If not, apologies.
I have had a old '77 - '78 Marshall Superlead head. A 1959 model. I bought it about 11 years ago. When i bought it, i put new tubes in and tried to bias it. The bias pot was knackered and i tried to replace it, damaging the PCB traces. I opted to throw in an earlier turret board i purchased from a kit vendor. I cut the old board out, made the new board then shelved the project for a decade or so. In the mean time, i obtained the period correct replacement from a mate and i have just recently installed it. I fired it up for the first time, standby off. Got 6.3VAC on the filaments as expected. I had doubled checked the voltage selector so i know thats good. I flicked the standby on and it immediately blew the mains fuse. I hunted around for my fuses and realised i had a few, which i tried but it blew the mains fuse once more so i left it and ordered some more fuses. As i'm running 240V mains with a 100W amp, i went for 3A slow blow for the mains and 1A fast for the HT supply. Now this is where the rust comes in... If memory serves, a blowing mains fuse is usually either an issue with the transformer and/or associated wiring or the rectifier. I am hoping i simply had the wrong fuses and adding the right ones will allow me to power it up. I've double checked the power section several times and everything is in the right place.
If i have to check the transformer, i can simply disconnect the secondary taps from the rectifierand measure each side referenced to ground for resistance. If i wanted to power it up, could i connect it to the input of my multimeter? Each of the taps as i recall puts out about 280VAC (its centre tapped so 2x 280VAC). If i lift the ground and connect the secondary to the DMM, i should see about 550V - 600V. Is this a safe thing for the DMM or transformer? Is the DMM a good enough load? I am praying the PT isnt fried as i want to keep this old amp as original as possible.