Marshall Major Blowing Power Fuse

[Justin Thomas]

I don't think anyone is beating up on Larry or his ground scheme. I've actually used something like it that I came up with out of practical necessity. But to anyone who is following along HERE, we should police that...

Generally, it's not a big deal around here when someone makes a wiring error. But when it comes to Mains, it's a little different. It's the capability for a wall outlet to deliver a practically unlimited amount of current until something burns down, possibly your house, possibly yourself.

There's no way we can police the entire internet for errors, but we CAN police what goes up here. I'm also open to the possibility that the photographed amp is from a different country. But given the Black/White/Green, and that the Neutral seems to be fused instead of hot, then it's definitely a possible issue that goes beyond melted tubes or transformers.

There <ARE> a lot of people who are cloning and building based on layouts. That doesn't mean that we shouldn't warn future readers about it. In some ways, I do think we should even feel a certain social responsibility to do so, and explain why. But nobody is beating up anybody, simply calling for anyone following along to pay attention. A few years back there were pics of "boutique" amp posted - the power transformer had the HT terminals exposed, right beside the power tubes. Reach back there while that amp is in operation, ZAP. While no-one WANTED to beat up on that builder, that is a fairly egregious error for a commercial product... I think this is in the same class...

No disrespect to anyone involved here is meant by me.

Justin

[Tom Phillips]

Guys take it easy. This pics is a drawing made from a user who dīnd.t understand nothing by basic circuits at the moment trying to understand what Larry Grohmann aka Novosibir on metro forum trying to explain...

Understood. However, my post was to point out that incorrect information was conveyed by the illustration that was posted. Regardless of how much good information was previously discussed elsewhere, the information in post #114 is flawed and, by pointing it out, maybe the continued spread of the flawed information will be reduced.
Cheers,
Tom

[catalin gramada]

You right Justin but posting here a drawing with massive error claimed as Larry grounding scheme is a little bit to much.for me at least.This guy is a precise german mind and did for community a lot. cannot assign him this kind of errors such as cause he didn.t. Don.t you think ?
Cheers

[cluster]

sorry... is this better??

[catalin gramada]

[ATTACH=CONFIG]43949[/ATTACH]

sorry... is this better??

...f..k man...Sorry.can.t stop me...

It looks allright to me...but have to do a mention.still. It is a long red wire going through lengh of chassis. I think it mean the heater center tap. I said I think cause I remember he said he found the quiest spot for this CT is the first at least noisy spot. And he is right. I tried it. But from my practice I found it is not absolutely necessary to run there. You can found a quiet spot allover the chasis. Just be sure you don.t choose a noisy one like tranny bolts or power stage grounding lugs. I always walk a wire inside the chassis to find a quiet spot for a shortest path

[Justin Thomas]

I don't knock Larry's ground scheme at all. And Larry did not actually build the amp used in the picture, correct? But whoever built that particular amp did it wrong, at least as far as USA laws are concerned. I think what we're trying to get across to any new users here is, "this is largely correct or safe to use for an overall ground scheme, but please do not just blindly copy THIS PARTICULAR amp as far as mains wiring goes." Larry is certainly not responsible for anyone who uses his grounding but makes mistakes...

then again, in the USA, there will always be SOMEone who will look for a way to make a few million in easy lawsuits... so by hammering this point home, we may actually be SAVING Larry from a LOT of hassle. Bottom line: no disrespect toward Larry intended. But, that amp's mains is wired wrong and should not be copied.

Justin

[catalin gramada]

Hundred percent agree

[cluster]

does anyone have a proper Larry Ground layout on hand they could post??

[catalin gramada]

Wich version? You have to follow the directions for US users if you live in States as I understand due to the main safety conditions. I live in Europe and here is equal as time we can turn the main plug in wall socket means live and neutral wire revert

[cluster]

Wich version? You have to follow the directions for US users if you live in States as I understand due to the main safety conditions. I live in Europe and here is equal as time we can turn the main plug in wall socket means live and neutral wire revert

I live in Canada, so it would be a USA version of the scheme.

[Justin Thomas]

The actual layout would be different, because your Major is different. Basically, the Larry Ground system seems to be what is called a "Galactic" one - some grounds are brought together and met at one point, a few others at another point... so using the photograph of the amp posted, just bring the noted and listed points together and ground them somewhere logical for the chassis design of your major.

The "problem" with the amp pictured is the mans wiring and the fact that the Earth Safety Ground is mislabeled. But the actual grounding scheme is correct for the Larry Ground scheme. The most important thing is that your green wire from your mains/power cable is the ONLY thing grounded at that point, and has to be bonded to the chassis. I will use a bolt with a keps nut, and then solder the whole thing straight to the chassis (if it's steel). Also a good idea to leave that green wire a bit longer than the other two, so that if the amp falls and the cord is ripped out or damaged, that green wire is the last one to break/tear free.

As Merlin points out, it's the single most important connection in your amp... otherwise, just go down the notes in the pictured amp and do the local "star grounds."

Justin

Edit: the other option would be if someone could mark up a schematic of the Major and show which ground point to with which... and a full-size internal chassis shot of EVERYthing may help for finding a good point. Like somebody did with the Spitfire a few years back...

[catalin gramada]

Don.t run high pulse ripple through chassis. Do the mods wiring as I allready showed you and see if you.re happy with that. There are just two wires to run



This is compulsory for any good practice to do from my point and have nothing in common with International safety reglementations
Use black wires to be in accord with wiring code if you want...

[cluster]

Don.t run high pulse ripple through chassis. Do the mods wiring as I allready showed you and see if you.re happy with that. There are just two wires to run

[ATTACH=CONFIG]43958[/ATTACH]

This is compulsory for any good practice to do from my point and have nothing in common with International safety reglementations
Use black wires to be in accord with wiring code if you want...

I understand the blue wire but not sure I understand the red one. Red is the bias ground. You're suggesting to lift the 2 yellows at the can ground and solder red to the two yellows?? Where then would the red/yellows be grounded?

[catalin gramada]

The red wire I sugest to run is not bias ground but center tap from bias secondary winding .Do you see a black wire on small turret board ? those wire is bias reference to the ground. Just check and ensure is firmly tight to chassis

First check if secondary bias is made from two sections and green wire and yelow are related as center tap. I think so but not sure hundred percent. Please check first. One of this wire (green or yelow) is bias center tap for sure. I.m not sure for the other. but my thought is your bias winding is made from two sections as HV secondary is.

[catalin gramada]

You bias looks like that at the moment (it should - please check green and yellow wires). charging current goes through chassis.



Not red and yellow but green and yellow. But check first . It is possible to be a split winding and both wires to form a center tap as I showed you in drawing , but also is possible one wire to be bias center tap and the other to be related to another winding (eg. heater CT). In this case you will lift just the wire represent bias center tap and solder this wire to the red one I showed you.



You need to run just the bias center tap directly to the bias cap instead the chassis ground lug. But if you bias center tap is made by those two wires (green and yellow) you have to connect all of them