Need Some Advice re my JCM800 4212 50w Combo?

paul-e-mann

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So I bought a JCM800 4212 a few months back and it doesn't sound so good. It was from seller on Reverb and we met in a car park about half way between our respective homes so I didn't get a chance to listen to it before buying but the seller had 100% good feedback. Also I figured it's 30-something years old so it might need some TLC to get it sounding good again. I used to own a 100w version of the same amp that I'd bought new in the mid-'80s that sounded better and had more gain on the dirty channel too.

I took the amp for servicing and the power valves were replaced, also I was advised to use the clean channel and I think the technician put a preamp valve in that causes the clean channel to break up more readily, he also told me to use pedals for overdrive and forget about the dirty channel but that's not really why I bought the amp or the way I'd intended to use it. The technician checked it for faults but it wasn't tested in a 'subjective' way, if that makes sense, i.e. for tone.

The clean channel sounds quite woolly, lacking in treble which is what makes me think there might be a valve that breaks up easily that's been put in there for the clean channel and there's still not as much gain as I remember getting on the dirty channel of my 100W version, yes it certainly overdrives but not as nicely as I'd like it too and I'm having these tonal problems
I've tried a couple of OD pedals on both channels (Bogner 'LaGrange' and a Tube Screamer Pro) and yes I get more gain but they don't sound very nice, there's a lot of background hiss when I use either the OD pedals or my Orange Kongpressor pedal with the 'squash' turned up, also my Boss DD200 sounds 'not right' through this amp, I have to turn the effect level WAY down before it begins to sound some approaching what I was used to getting but I can't help thinking the amp is affecting it.

I'm not connecting any pedals up to the effects loop.

I returned to playing electric guitar a couple of years ago but in the past when I'd bought new or used valve amps I'd automatically replace at least their preamp section valves with Mesa Boogie items as they always sounded better than the stock Marshall / Peavey / whatever items.

Should I replace the preamp valves with Mesa Boogie items this time around or are there maybe other brands that would sound better in this amp? Maybe I'm not approaching this in the right way either. Ideally I'd like the clean channel to sound fairly bright as well as clean and the dirty channel to have a decent amount of gain; I never needed to use an additional overdrive pedal with my last dual-channel JCM800

Are there any of the 5 preamp valves in this amp where something other than a 12AX7/ECC83 might be a better choice?
The last time I owned electric guitar equipment there wasn't the benefit of the internet for sourcing valves or anything else but now I find I'm spoilt for choice to the point it's become mind-boggling. The only reservation I have is that I won't use any Chinese-made items as I boycott any goods of Chinese origin.
Could it be that there's other things not right with the amp? I've not checked what brand(s) the preamp valves are yet and I took it to a reputable technician for servicing.
Any opinions or advice would be greatly appreciated, I'd very much like to get this amp sounding good again
You just spent good money with the tech, take it back to him and tell him the amp sounds nasty and you want both channels to work properly. If he cant then get a refund and take it somewhere else.
 

Georgiatec

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First up...Your tech should not be telling you how to use your amp. He should be making the amp function how it is designed to function.
Old amp not sounding good...re-tube and re-cap it. No ifs or buts until you are able to have the original tubes tested. Most people selling amps put a load of junk tubes in that they would never use in a month of Sundays.
 

purpleplexi

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Seems like you're in the UK - whereabouts? Firstly that amp should not sound dull - it should have enough treble to cut glass. Did the tech check the bias? If you are in the UK and anywhere near MiltonKeynes I would strongly suggest taking to to Marshall. They are the cheapest Marshall repairers anywhere - even though there's (obviously) no warranty they will check it over for free and tell you what it will cost to put it right before they do anything. I think we can all be confident they know what they're doing. In my experience if they do have to do anything they only charge for the parts which are usually pretty cheap.
 

steveb63

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First up...Your tech should not be telling you how to use your amp. He should be making the amp function how it is designed to function.
Old amp not sounding good...re-tube and re-cap it. No ifs or buts until you are able to have the original tubes tested. Most people selling amps put a load of junk tubes in that they would never use in a month of Sundays.

^^^^^^^^^^^ This says it all very succinctly.
 

Crikey

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Seems like you're in the UK - whereabouts? Firstly that amp should not sound dull - it should have enough treble to cut glass. Did the tech check the bias? If you are in the UK and anywhere near MiltonKeynes I would strongly suggest taking to to Marshall. They are the cheapest Marshall repairers anywhere - even though there's (obviously) no warranty they will check it over for free and tell you what it will cost to put it right before they do anything. I think we can all be confident they know what they're doing. In my experience if they do have to do anything they only charge for the parts which are usually pretty cheap.
Id take it to Marshall
Worth the tour
 

HowlinWolf55

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I too have recently acquired a 4211 combo and the problem I have is that on the boost channel the master volume is quietest at around 1.5. When I turn it from there to zero it gets louder. And it also gets louder more conventionally starting from 1.5 and turning upwards. And when I’m at 1.5 to zero, it seems like the gain is more saturated as opposed to going upwards from 1.5. Also when I’m at 1.5 to zero, the treble middle and bass knobs seems to work ass backwards too, like the treble increases going from 4 to zero, I think 4 was the lowest amount of treble… I can’t remember 100% at this moment but you get the idea. Middle and bass also increased as I turned down from a certain ‘lowest point’.

I’m pretty certain these problems only occurred on the boost channel, so if anyone knows what the best way forward would be in this situation, please let me know. This combo is so heavy taking it to a tech is my last choice. But I also don’t know much about amps but I am open to learn and I could solder in and out a few resistors or swap a pot or two on my own. :)

To the OP, I hope you get yours sorted out, cheers. :cheers:
 


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