Need history lesson on 4210 circuit changes

[daz]

A member at another forum who may or may not frequent this one was telling me of the changes in the marshall JCM800 channel switchers which i'm looking at right now. I have had 3 of them in the past and one was a far better sounding amp than the other 2. It was the earlier one with 6550's. However, it wasn't the tubes that made it better because i modded it for EL34's and it still killed the later ones i had. This person, John Phillips told me there were 3 circuit designs. the first being FAR better and far different than the later ones. I think this one was the first year they made the switchers or maybe the second too. Then he said they changed them drastically for the next year or 2. Finally in i believe '85 they changed to EL34's and a slight circuit change somewhere else too.

problem is, he's in england and didn't even know they made the early ones with 6550's because the non USA export models according to him were EL34 from day one. This is why i posted here.........because while he seemed to know a lot about them in great detail, the one thing he doesn't know is what differences the export models saw. And therein lies my question. I want to buy another 800, the 4210 1-12" combo to be exact. But knowing how much better my early one i had sounded i want to make sure i get that same circuit. problem is, it's been a long time and i cannot recall what year it was. It was one of the pre-EL34 models but i cannot recall what year. So i need to know what changes took place in these amps in the years preceeding the change to EL34's which should be 82-84 if i'm correct. I think 82 was the first 800 channel switcher and 84 was the last one with 6550's. In any case, does anyone know which year between 82 or whenever they came our and 84 there were significan't circuit changes? john mentioned the change can be determined by looking for transistors used in place of the later IC's. Anyways, i need to know which years had the earliest circuit. Thanks.

[Ray Ivers]

daz,

I only know of two circuits for the 4210/4211/4212 amps, but I'm by no means a Marshall-minutiae expert. Here's the early circuit, AFAIK:

http://www.schematicheaven.com/marsh...v_50w_4210.pdf

... and here's the later circuit (again, AFAIK):

http://www.schematicheaven.com/marsh...h_50w_2205.pdf

The two circuits are quite different; alternate switching method and post-PI MV in the early circuit, among other things.

Ray

[daz]

Originally Posted by Ray Ivers

daz,

I only know of two circuits for the 4210/4211/4212 amps, but I'm by no means a Marshall-minutiae expert. Here's the early circuit, AFAIK:

http://www.schematicheaven.com/marsh...v_50w_4210.pdf

... and here's the later circuit (again, AFAIK):

http://www.schematicheaven.com/marsh...h_50w_2205.pdf

The two circuits are quite different; alternate switching method and post-PI MV in the early circuit, among other things.

Ray

he did mention the change in the master and the different switching, but do you know which year that happened in? I need to know what the last year i should look for is to make sure it's the original circuit. I think it's either 82 or 83 that was the last year of the initial circuit but i'm not sure. the only thing i was sure of is that in 85 or 6, pretty sure 85, they changed to EL34's, and that amp sucks compared to my earlier one. The tone wasn't near as good and both amps like that i had would start to get mushy and lose defination when they'd warm up fully. I was thinking as long as i got any year with the 6550's i'd avoid that. (not because of the tubes....i changed my 6550 one to 34's and it was still far better than the later ones) But now he's got me thinking even with the 6550 models there is a revision that may leave me with the same troubles i had with my later el34 models. I just want to avoid that by making sure the amp i buy is going to be like my good 800. Wish i could remember what year it was !

[Ray Ivers]

daz,

do you know which year that happened in?

The first schematic I posted is dated September 12, 1983 and earlier, and the second is dated June 3, 1987 and later. I assume the changeover occurred some time between these dates.

Ray

[daz]

Originally Posted by Ray Ivers

daz,



The first schematic I posted is dated September 12, 1983 and earlier, and the second is dated June 3, 1987 and later. I assume the changeover occurred some time between these dates.

Ray

Thanks Ray. That makes perfect sense because from all i've gathered i figured it was the same circuit for the 1st 2 model years, and your finding would speak to that. the 83 change was near the end of the year so it would seem 82 thru most of 83 would be the same initial circuit. Now i just have to find an amp where the owner is showing the date sticker like one i've been following on ebay. unfortunatly that one is 84 so i guess the search goes on. but at least now i have a date to go by. Thanks much.

EDIT: i know the 87 one is long after the switch because they changed the output section in 85, and i'm positive the rest of the circuit is not the early one. I think it happened sometime between may 83 and before 85. And i was thinking you said the newer circuit was dated 9/83 and so i took that as meaning it began production sometime around there. But after looking at the schematics i see the 9/83 date was a revision of the initial circuit, so that makes it likely it stayed that way thru the rest of 83 and who knows how much longer. So anything dated 83, any month, should be ok. I guess sometime in 84 it changed which means even an 84 may be the one but also may be the newer circuit because it probably happened during that year. 85 is the final EL34 model so it has to have changed sometime in 84. The 84 i was looking at was dated october 84 and according to John who looked at the pic of the board it's not the initial circuit. So i bet it changed in early 84.

[Slobrain]

Hay Daz,
Have you tried to contact Marshall on this amp and who the original engineer was? Maybe they still have records on what changes happened when.

Its strange how big amp companies can change circuit design only to make some amps worse... Who is doing the amp sound listening test in these companies

BTW, how was the distortion on that certain marshall 4210 you liked?

SLO

[daz]

Originally Posted by Slobrain

Hay Daz,
Have you tried to contact Marshall on this amp and who the original engineer was? Maybe they still have records on what changes happened when.

Its strange how big amp companies can change circuit design only to make some amps worse... Who is doing the amp sound listening test in these companies

BTW, how was the distortion on that certain marshall 4210 you liked?

SLO

Great....thats what i liked about it. Diodes or not.