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Marshall 8100 Upgrade To Jcm800


ROBERTLATHAM1
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HELLO,

I AM NEW TO THE BOARD HERE! SO HELLO ALL! ALRIGHT ON WITH IT. I AM AN ELECTRICIAN NJOT ELECTRONIC TECH SO IM LIMITED. WHAT I WANT TO DO IS UPGRADE/MODIFY MY MARSHAAL 8100 VALVESTATE HEAD TO A MARSHALL JCM 800 HEAD. FIRST IS THIS POSSABLE AND SECOND WHERE CAN I FIND THE WIREING DIAGRAMS TO DO SO?

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No, it's not at all possible.

A 'Valvestate' Marshall is a transistor amp with one 12ax7 pre-amp valve wired into the circuit somewhere (i'm not overly familiar with transistor amps).

The two amps are as different as black and white. If you could turn a Valvestate into a JCM800 everyone would be doing it.

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This place has loads of schematics. I'm not sure about the JCM800 but it's basically the same amp as the earlier JMP 50 or 100watt amps. They even have the same model numbers.

The 100watt JCM/JMP's are the '2203' model and the 50watt heads are the '2204'. They usually have the pre-amp and power-amp circuits separately and I 'think' they are the same for the 50+100 watt models.

This is the link: http://www.drtube.com/guitamp.htm

PS:I forgot to say that those two amps (2203+2204) are the 'Master Volume' versions.

Edited by JTM45
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jtm 45 thanx again man i got the schematic's i need my brother is a tech ans feels he can build the head fairly easy but the price is what he said mught concern me it got to be cheaper than $1600 which is price for re-issue of the jcm 800!

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Just a suggestion, but it might be cheaper to find a used "donor" amp and mod it into shape - lots of used 50 watt amps out there you can pick up cheap, and you'll have a chassis w/sockets, pots, etc. and transformers for probably less than you can buythe trannies new! Just gut it and build a JCM800 in it.

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yeah thats a good idea i was talking to my brother who is a electronics tech and he said that the parts were going to be costly , but i still believe that i can build the jcm cheaper than buying one used ofcourse.

thanx for the suggestion that is prob the direction i will go. i was hopeing i could have did mods to the 8100, but i dont know electronics well enough to know if that was posable. jtm45 says no way

anyways thanx

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I can almost guarantee that buying a used JCM800 is going to be cheaper, easier, and more reliable than attempting to convert the 8100 box into a completely different amp.

Seriously, if you want to learn how to build an amp, cool. But unless your brother is going to be there to rip into the box every time it cuts out on you on stage or wherever, it's going to be a major PITA.

Before everyone rips into me about discouraging you, let me just say that I think it's cool to learn how to build amps that way. That's how Leo Fender and Jim Marshall did it, too. But if you want a solid, reliable amp that's even close to the JCM800, it's going to take a lot more time, energy, and money than what a used JCM800 will cost you in the first place. My advice would be to take the 8100 and trade it in on the JCM800 if that's what you really want.

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You're never going to get anywhere trying to convert the Valvestate (or any other solid state amp) to a JCM800 - there are simply too many differences! However, there are plenty of inexpensive tube amps patterned after the classic Marshall circuit architecture that would make an excellent starting point - Laney, Traynor and even the Pignose G40V spring to mind as possible candidates. As for the reliability issue, as inconsistent as Marshalls have been over the years, especially since they started using printed circuit boards, I'm not sure I wouldn't prefer a well-made homebrew. Remember, one man's "homemade" is another's "handmade custom"! :D

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...Another electrolytic-blowing, Marshal-hating, point-to-point-wiring

fanatic...

:D Not a hater, but they sure don't hold up like they used to, and I've really got nothing against pcboards, so long as they aren't badly-designed, impossible-to-repair rubbish..., I guess I just expect too much!

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I will just bet you are in love with SMT also! That and double-sided PCB tracks! If it weren't for real good desoldering irons, I would be out of business. SMTs aren't as bad as I first thought they would be but you don't troubleshoot the little boogers. Just pull and replace. 63 year old eyes don't do too good at that.

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I hate SMT now that I don't have access to a Pace rework station :D

I still like Marshalls, but like everything else, you gotta be choosy about which ones you buy and how you take care of 'em. Mesa, Soldano, Genz Benz, and Rivera kick a$$, but sooner or later they're going to be like Marshall and set up everything for massive mass production and endorsement deals rather than quality sound and legendary reliability.

But give me an old JCMSlash or 1987 Silver Jubilee and I'll rebuild it as often as necessary to keep it going...

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:D To each his own, I suppose - I personally thought the Jubilee was pretty near horrendous (like all JCM900s, it has more silicon diodes in it than an Ibamez Tube Screamer! B) ), but if that's what you like, cool. It just doesn't sound anything like a classic Marshall. :D

Yeah, doc, SMT sucks, but my least fav'rite initials right now are DSP! :D

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I have to agree with 'Lovekraft' about the 900's and anything Marshall made after the 800's really(and i'm not overly keen on the standard 800's). Just not my cup of tea at all!

My current Marshall is a 1979 JMP 50watt Master Volume (2204 model) and I find the sound is so much more 'wholesome' than the newer designs. It's got a lovely warm sound and none of that 'fizzyness' that i hear in the newer amps.

Although the JCM800 series 50watt amp is basically the same model as mine it still sounds more 'artificial' to me. I have read that they put a few more diodes in the pre-amp circuit on the 800's so if this is correct that could be the reason for the difference in the sound.

I wouldn't mind trying to change the PCB in mine for a turret-board PTP type circuit to see what sort of difference it makes to the sound.

Edited by JTM45
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I would say to try ebay for a cheap used amp. I got a Laney Supergroup for £140 including p&p. It needs all new valves but sounds great. It's a 1970's amp and has a great classic tone.

If you want to build an amp you could try www.18watt.com. It is a site dedicated to building marshall's 18 watt amp from the 60's.

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wow ok opened up a can of worms here lmao! i really like the brown sound i.e eddie vanhalen marshall years. but i dont know enough about electronics to know good from bad i hear hard wired amps over board amps , carbon filled caps over silica honestly i dont know the difference. all i do know is that i really like the jcm 800 sound and the new triple lead 2000 is pretty sweet too! but being apoor broke electrician i guess my dreams of ever haveing a jcm 800 are just that! boo hoo lmao!

Edited by ROBERTLATHAM1
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