JTM 45/50 Build: Issues with high voltages

[martin manning]

The HT ground is electrically connected to the speaker ground anyway (so it's not dangerous), but it should be run directly to the reservoir ground.

The speaker jack wiring in the Mojo layout is correct but it is poorly drawn, showing the connections from what is normally the underside of the jacks.

As shown in the pictures the jacks are not wired per the diagram under either assumption (top or bottom view).

[cbass]

Is that a wire going from the fuse holder to the speaker jack.
I'm scared

That side of the fuse holder is connected to ground. Not a good idea IMO to fuse the PT HV center tap when you have a negative bias circuit that also relies on that center tap. Funny things happen to the bias supply voltage when the fuse is open. Bias caps may suffer.

Oh yes like Marshall originally done it .I would ditch the fuse for the ct and put it on the b+ just because its the way they did it in the old days doesn't mean it's better.

[bt2513]

Awesome! I knew something was screwy there. I must have checked it against the diagram a dozen times and could not reconcile the differences with other diagrams from the web. I just assumed that the diagram was correct. Obviously, I still missed something.

Going to wire it as yall suggested when I get home from work.

Thanks!

[bt2513]

I want to thank everyone hanging out the Marshall forum here for your help - especially, Martin Manning!

I went home and rewired the output jacks - its funny that I checked the wiring against the diagram but didn't bother to check the cliff jacks themselves as they were flipped around. Did I mention I assembled the bulk of the kit when I was home sick with a fever earlier this year?? Lesson learned...

Anyway, I also took a look at my input jack wiring and realized I had made the same mistake on all four jacks. I rewired those as well.

After all of this, I fired it up and the amp really sings! The tubes still need to be broken in but overall I'm very satisfied with how it turned out. I'm planning to swap out tubes and maybe try some KT66s in the amp (after swapping some components) but for now I'm just happy to play the amp!

Thanks again everyone!!!

[martin manning]

Great, glad to hear it's working! Personally I'd be leery of the meter you're using... It seems to have given you some odd readings, and drawing a lot of current during a voltage measurement (the arc you saw) is not expected behavior.