MajorNut1967

I thought it might be reasonable to have a thread dedicated to the technical and repair aspects of the Marshall Major, since it is one of Marshall's oddball amplifiers. In particular, it will be dealing with the models 1967 lead, 1978 bass and 1966 PA. One thing I think we should stay away from discussing here is the "Marshall 200” (otherwise known as the “Pig”) as it is the earliest of the 200 W amplifiers from Marshall and is not kin to the Major; it is a totally different animal. Therefore, questions and contributions are all welcome!

Marshall Amps

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MajorNut1967

Here's a corrected Schematic for the 1967, the one on the net has some mistakes on it.

demonufo

Sweet. Thanks for that. I'll probably never get to see one, but I've saved it to hard drive anyways.

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RickyLee

That is a modified Major in the picture there, Major?







Looks to have two extra 9 pin valves?

Jon A

I only see one extra 9pin on that chassis, but the chassis is a 1969. Not to be confused with the 1967 schematic? Yes?

MajorNut1967

I'm not quite sure what you asking here? The model# for the Major Lead is "1967" so whether is a 1968-74' year the model# is still 1967.

As far as the Chassis all Major chassis have the extra 9pin Noval (4 total, stock only uses 3 holes). Here's an example of a bare freshly re-done Chassis. The picture I used in the Beginning is just for reference, that ones been monkey'd with!

Jon A

Ok so the 1967 schematic applies to the picured 1969 chassis? The chassis has 4 9pin valves (tubes) in the photo, was there an option for the added 9 pin (ECC83 or ECC82)?

MajorNut1967

Anytime Demon, hopefully we can get you to have the itch and build one sometime!

demonufo

Y'know if I wasn't so p!ss poor broke for the unforeseeable, I'd definitely be considering one. That's quite a scary build proposition though, compared to the easy sh!t I'm used to.

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MajorNut1967

Basically that should be the SCH for that 69', but as I said, "that one's been modded." The reason there is even a 4th 9pin is that there is the PA models need it for the extra channels! Here look at the 1966 PA SCH below. Cheers!

http://www.webphix.com/schematic%20h...66_200w_pa.pdf

MajorNut1967

Actually the BABY MAJOR build isn't so bad, well neither is the 200 watter; no harder then a 1959!

Jon A

Excellent, thank you!

MajorNut1967

Sorry I don't articulate things properly sometimes. I mean it's your language, I just use it once in a while! LOL

Jon A

Nice to know what the normally empty hole was for. Blokes in the USA see an empty hole and just "gotta fill it". Played many decade ago with a smokin' guitarist that had two, both full stacks. Awesome sounding.

Papus

Thanks for posting this vital information
I'm going to have my amp tech attempt a design at a baby 50w or even 25w "Major"

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MajorNut1967

I don't know a whole lot myself, but if I can be of any help let me know.

Toastmaster

Is this trip necessary ?

MajorNut1967

"Is what trip necessary?"

Toastmaster

I was trying to be Mickey Spillane,Sir !

MM54

I must say, if I wasn't flat-out broke, I'd be quite tempted to build a "baby" Major. Looked the whole way through that schematic, and it's quite interesting

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MajorNut1967

yes unfortunately economics have a say so in us building our toys. I really wish one of you guys on the forum had the resources to build a baby major so we could just walk through the project and I would help as much as I could, as well as the great techs that are here.

It is a very interesting looking amplifier: part Marshall, part fender and part hi-fi. Which is why they sound the way they do.

MM54

It is really interesting. I'm adding it to my list of things that I will do, eventually

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MajorNut1967

Disclaimer: this article is provided as information only! If you are not qualified and experienced to work on high-voltage tube amplifiers do not attempt the repairs yourself under any circumstance! Take your amplifier to a qualified technician. Any mistakes made can result in serious injury or death.

This article pertains to safety upgrades for the Marshall Major specifically removing the polarity switch from the circuit and the death cap. On some of the earlier Marshall Majors (primarily the US models)there is a polarity switch and the so-called "death cap". The original purpose of the switch was to polarize the hot and the neutral or N & L respectively, to the correct polarity on the two-pronged mains cable; as you could plug a two-pronged into the wall more than one-way and risk electrical shock through the chassis. However, the hazard lies within the capacitor that is utilized in the circuit, if the capacitor goes bad or direct shorts there is a risk of being electrocuted. So the best thing to do is to remove the polarity switch and death cap and that is what we will be talking about and how to do it.

First of all you will know you have a polarity switch on your amplifier if there are three toggle switches on the front panel, from left to right they are polarity, main power, stand by. See photo number one(circled in red) this is the polarity switch. The object here is to remove the switch and death cap out of the circuit, you don't have to physically remove the switch from the chassis, as it will leave an empty hole there. The switch itself can have variations but it does the same thing, sometimes there is a DPDT switch "six lug" and sometimes there is a SPDT "three lug” I also heard tale of one setup that had all six lugs of the DPDT connected, if one of you guys has one of those let me know.



Normally there'll be three yellow wires connected to the polarity switch. once you have the chassis removed from the cabinet and safely discharged all the filter caps; you can go ahead and just clip the three wires cleanly and then heat shrink wrap them with heat shrink tubing to insulate them and then also wrap 600 V electrical tape around the ends as extra added insurance. Now after that point you have to make a decision on how you handle the mains cable, one you can install an IEC type mains socket on the chassis or if you want to stick to detail and just use a cable through a strain relief you can do that also. Remember that you have to replace the two conductor Main cable with three conductor (earth/ground, hot/L , neutral/N) 14gauge cable. If you are going to be gigging with the Marshall Maj. regularly I'd suggest using the IEC connector, but that involves some cutting and shaping of the rectangular hole.


(THIS IS THE ORIGINAL CIRCUIT)

(THIS IS WHAT WE ARE TRYING TO ELIMINATE)

STEP 2: Now let’s deal with the actual wiring, first do not use a machine screw, star washer and solder lug to create the earth/ground to the chassis. Get the biggest hottest soldering iron you can find and directly solder the ground wire to the chassis! Yes, I know not everyone has a gorilla 120-watt soldering iron like I do, but borrow one if you can, look make the best connection to the chassis you can. Then if you use the IEC connector wire it according to standard (see IEC photo). If you hard wire the mains cable, go ahead and push enough cable through into the chassis so you'll have enough to work with and then lock it in place with a strain relief and wire accordingly. Now depending on what part of the world you are in wire colors can very but in the US three conductor appliance type cable will be colored coded as: black= hot, white= neutral, green= ground. In the rest of the world: Brown=line, blue= neutral, green or green with a yellow tracer= earth. Now in the IEC photo and in photo four you will see that I change the main power switch to a double pole double throw or DPDT switch (or you could use a DPST "double pole- single throw” switch if you can find them). I do this as an extra measure of safety as you can switch off the neutral and the hot simultaneously. I recommend you do this.

(IEC Wiring Diagram)

(END RESULT & SAFER)

Lane Sparber

NICELY DONE, Major! You are really giving me a run for my money here.

I will say that all of the mods that the Major describes above deal specifically with the Majors, however the ideas he discusses pertain to a LOT of amps. For example...a lot of Fenders used the "death caps" too, and they should always be removed whenever they are found-in conjunction with installing a 3 pronged grounded power cord.

EXCELLENT work, sir!

-Lane

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WARNING: Tube amps contain LETHAL voltages long after they've been unplugged. If you are not familiar with the safety procedures involved when working on high voltage circuits (such as how to safely drain the filter caps), then PLEASE take it to a tech to stay safe...and alive.

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MajorNut1967

Well "Thank you!" However, under no circumstance would I be giving you a run for your money. I just hope that some standard of humbleness can be maintained as well as imparting knowledge & experience to people.

It is funny how much the polarity switch was implemented in the 50-60’s and how dangerous it could be. And not having any quick & safe way to know it was set right.

Papus

It was the 1950's - back then people actually used their brains and did not require "caution, contents may be hot" on their ****en coffee cups!!!!!
Thesedays people are a lot dumber and require instructions and warnings on EVERYTHING!

****EN LAWYERS, they ruin everything!

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MajorNut1967

Absolutely Bro! +10000000000000