Diode Rectifier Wiring Question

[ThreeChordWonder]

For an upcoming Marshall Superlead 100 Watt Copy.

I'm going to be using UF5408 diodes laid out as shown (if it's correct).

Just want to be sure I've got the outputs from the rectifier the correct way around.

Thanks

 

[StingRay85]

If you need to ask that here, you are either very insecure, or maybe you shouldn't be building your own amplifier. But the layout is correct, that's a bridge rectifier in case your PT secondary doesn't have a center tap. If it does have a center tap, you shouldn't be using a bridge rectifier like this.

Also, make sure to ground it on the - (black pole) of the reservoir capacitor.

 

[ThreeChordWonder]

If you need to ask that here, you are either very insecure, or maybe you shouldn't be building your own amplifier. But the layout is correct, that's a bridge rectifier in case your PT secondary doesn't have a center tap. If it does have a center tap, you shouldn't be using a bridge rectifier like this.

Also, make sure to ground it on the - (black pole) of the reservoir capacitor.

Everyone starts somewhere, and it's better to ask than fork up. I get confused because you sparkies got the electricity flow direction wrong, and have been confusing everyone since, and I was confused because the positive feeds seem to come off the diodes' cathodes.

Thanks anyway.

 

[ThreeChordWonder]

PS yes the PT has a center tap, but in the wiring I'm following (Mojotone Marshall Superlead 100) the center tap doesn't go to the rectifier, via the standby switch or not. Instead it goes to two of the 50/50 uF filter caps.

 

[StingRay85]

For me personally, as a chemical engineer, electrons are negatively charged and there's no such things as a positive current flow

 

[StingRay85]

PS yes the PT has a center tap, but in the wiring I'm following (Mojotone Marshall Superlead 100) the center tap doesn't go to the rectifier, via the standby switch or not. Instead it goes to two of the 50/50 uF filter caps.

The schematic that you posted uses a PT without center tap.

If you have a PT with center tap, you need to put two diodes in series on each side of the secondary, and ground the center tap of the PT at the reservoir cap (even better: put a fuse in between).

Double check what you have

 

[PelliX]

I get confused because you sparkies got the electricity flow direction wrong, and have been confusing everyone since, and I was confused because the positive feeds seem to come off the diodes' cathodes.

Eh, depends on what you (or "we") mean here. There's conventional current flow which is basically what most of the world deals with and what you're taught at first at school. "Current flows from the positive to the negative terminal in a circuit". Then there's actual current flow which is the inverse; valves are a case where you have to understand "real" current flow. After all, electrons are boiling off the cathode and attracted by the plate (anode). I believe there's a certain Mr Franklin we have to blame for that incorrect assumption (conventional current) which has become the de facto standard.

In a diode current (conventional) flows alphabetically; that is to say from the anode to the cathode. The electrons move in the opposite direction, but they "hardly move"... and that's another can of worms right there.

For me personally, as a chemical engineer, electrons are negatively charged and there's no such things as a positive current flow

Not just as a chemical engineer - electrons are negatively charged. Full stop!

 

[ThreeChordWonder]

Mechanical engineer here - liquids in pipe flow from high pressure and / or elevation to lower, which is probably where the [wrong] assumption came from.

We had to do electrical (electronics and power) in our first two years because most machines ran on electricity, even in the 1980s.

Anyway.

Two hydrogen atoms walk out of a bar.

One says to the other "I think I left my electron behind".

"Are you sure?"

"Yes. I'm positive."

 

[PelliX]

Mechanical engineer here - liquids in pipe flow from high pressure and / or elevation to lower, which is probably where the [wrong] assumption came from.

Ha, if only it were that logical. Benny was comparing charges in various substances and made a 50/50 guess. He was wrong...

"When Benjamin Franklin made his conjecture regarding the direction of charge flow (from the smooth wax to the rough wool), he set a precedent for electrical notation that exists to this day, despite the fact that we know electrons are the constituent units of charge, and that they are displaced from the wool to the wax -- not from the wax to the wool -- when those two substances are rubbed together. This is why electrons are said to have a negative charge: because Franklin assumed electric charge moved in the opposite direction that it actually does, and so objects he called "negative" (representing a deficiency of charge) actually have a surplus of electrons.

By the time the true direction of electron flow was discovered, the nomenclature of "positive" and "negative" had already been so well established in the scientific community that no effort was made to change it, although calling electrons "positive" would make more sense in referring to "excess" charge. You see, the terms "positive" and "negative" are human inventions, and as such have no absolute meaning beyond our own conventions of language and scientific description. Franklin could have just as easily referred to a surplus of charge as "black" and a deficiency as "white," in which case scientists would speak of electrons having a "white" charge (assuming the same incorrect conjecture of charge position between wax and wool).


However, because we tend to associate the word "positive" with "surplus" and "negative" with "deficiency," the standard label for electron charge does seem backward. Because of this, many engineers decided to retain the old concept of electricity with "positive" referring to a surplus of charge, and label charge flow (current) accordingly. This became known as conventional flow notation."

 

[2L man]

PS yes the PT has a center tap, but in the wiring I'm following (Mojotone Marshall Superlead 100) the center tap doesn't go to the rectifier, via the standby switch or not. Instead it goes to two of the 50/50 uF filter caps.

This kind circuit keep series capacitors voltages"balanced" without two parallel/series resistors which do not function very well!

Electron flow is not needed in electronics which use current and which flow from positive to negative!

 

[PelliX]

Electron flow is not needed in electronics which use current and which flow from positive to negative!

Well, depends. Vacuum tubes are an obvious example of electron flow, but so are transistors and other semiconductors when you actually get into *how* they work, i.e. the electrons vs holes, etc.

 

[Pete Farrington]

The schematic that you posted uses a PT without center tap.

If you have a PT with center tap, you need to put two diodes in series on each side of the secondary, and ground the center tap of the PT at the reservoir cap (even better: put a fuse in between).

Double check what you have

The JMP / JCM 100 watters eg 1959 SL use a FWB rectifier, the HT winding CT is used to provide a 1/2 voltage reference for the reservoir caps https://www.mojotone.com/Amp_Kits/British/British_100W_Bass_SCH.pdf
The CT doesn't carry load current, so it seems best to describe rectification as FWB, rather than a pair of 2 phase rectifiers.

 

[StingRay85]

The JMP / JCM 100 watters eg 1959 SL use a FWB rectifier, the HT winding CT is used to provide a 1/2 voltage reference for the reservoir caps https://www.mojotone.com/Amp_Kits/British/British_100W_Bass_SCH.pdf
The CT doesn't carry load current, so it seems best to describe rectification as FWB, rather than a pair of 2 phase rectifiers.

Good point, I missed that one