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Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by GuitarInnovations, Dec 24, 2019.
If I squint....it sounds pretty good.
Power input wiring is messy, and I can't tell exactly, but looks like hot is fused, then goes to PT, while neutral is switched? That's not good--puts hot on the PT even when switch is in OFF position. Is chassis properly grounded to earth? Is there a stray red wire that goes nowhere?!?
In all that craziness, they did braid the secondary of the output transformer. If they had kept up after that it would be better but it could be worse. How does it sound?
Really doesn't look too bad, definitely better than what you would've gotten in a 70's Fender wiring job! I like the way the preamp is grounded with the single bus across the front of the board, less noise than multiple chassis grounds IME. Front control wiring could've been done a little better, those can be braided (and heatshrinked for added cleanliness) too for noise suppression, but that's not a hard project to do yourself. Tube wiring routing looks okay, grid wires look like they're nice and out of the way, but I'd prefer to see those taped or gooped to the chassis. Power supply area looks a little goofy, some of those wires definitely need a haircut and braid and schematic once over, but I doubt that part of the amp would contribute to noise or oscillation, it's just ugly!
All in all looks like a solid build, spend a couple hours braiding those front control wires and trimming some excess wire here and there and it will be whisper quiet, but it really shouldn't be too bad as-is.
Not bad, but not amazing. @Vanyu hit it on the head.
Err, safety first! Until there's a decent photo that shows there's reasonable chance the chassis (and hence any guitar plugged into it) is properly grounded, the advice has to be not to touch it with a 10 foot pole. A wooden one.
The white neutral wire from the IEC inlet looks to have a a significant burn mark (ie probably due to careless wielding of the soldering iron).
Bearing in mind that wire may often carry full mains voltage due to miswired wall outlets, that really should be replaced. Hence it may not bode well for the builder’s qc.
Is the mains grounded anywhere?
Ahem. I believe you meant to say 'Am the mains grounded anywhere'. Grammar are important.
I think that cheesy snap-in IEC receptacle is hiding the ground wire (I hope). Just a matter of time until the amp owner goes to pull out the AC cord for transporting the amp, and the whole dang socket and wiring come with it. If I'm doing an IEC inlet, I always get the metal ones that attach with machine screws.
its the mains socket ground anywhere?
Whats with the two resistors going to the EL84s? unless the resistors on the board go to ground instead of B+ they should connect to the resistors that go to ground at the opposite end of that section.
The small resistors are grid stoppers and large resistors are screen grid stoppers. The two 470K resistors that conjoin right before the grid stoppers are the grid leaks going to ground (or to -biasV in fixed bias). The resistors at the other end of that chunk are the P.I plate resistors, and it looks that they make their way over to the P.I under the board and connect to the plates through the blue and grey wires that seemingly terminate to nothing from the top. Looks to be a slick way of minimizing the wire run for the EL84 grids.
That's what I thought might be the case, but it's unusual.