Need Some Advice re my JCM800 4212 50w Combo?

[Firkwyte]

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

 

[Jethro Rocker]

Hmmm hard to say from just that description.
Firstly tech is nuts, you don't get an amp like that to run the clean channel. Ridiculous. He may well have put something different for a preamp tube in V1, I would check. That does not sound overly reputable to me. Did he check all the preamp tubes?
Generally There is no point in blindly putting Mesa pretubes in, for example, Mesa tubes are probably made by JJs at this point which may well be stock Marshall tubes as well.
Considering it's age, it may have very good preamp tubes and it may have weak ones. I would change out the first 2 preamp tubes with new known good ones and see it helps your problem first. Clean channel should get ice pick highs as required.
Past that I am clueless.

 

[PelliX]

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.

I don't know what you told him that triggered that response, but - who buys a JCM800 for the clean? Maybe more people than I know of, but hey.

there's a lot of background hiss when I use either the OD pedals or my Orange Kongpressor pedal with the 'squash' turned up,

If pedals are increasing the background noise substantially it's not the amp. The just amplifies what it gets, so any additional 'noise' must be coming from the pedals, cables, guitar - something before the amp.

I'm not saying there's nothing else wrong with it, but let's proceed logically.

 

[South Park]

You can start by replacing all preamp tubes with masa tubes . The high and low Chanel’s are on v1 so if one is bad both are bad . You should also check the bias on the power tubes . Is the amp modded

 

[Firkwyte]

Thanks for your comments, very much appreciated. I'm pretty sure Mesa are using Sov Tek as their source at the moment, I seem to remember reading that some place a while back. They're the kind where you can't see the heater and don't appear to glow when powered up if that's any help. I bought a full set earlier this year for a used Mesa amp that arrived with a mixture in it, only the power ones (2x Marshall EL84s) had the same names on them and one had been smashed in transit .
You're totally right though and it's exactly what I'd been thinking I didn't buy a dual-channel 800 to be restricted to a single channel. I can't mention names but the tech came recommended by a large valve supplier. That's quite a collection of amps you've got there, are you happy with the JVM? I've been contemplating one of those..

 

[Firkwyte]

I don't know what you told him that triggered that response, but - who buys a JCM800 for the clean? Maybe more people than I know of, but hey.
Exactly, that's what I was thinking whilst i was driving it home.


If pedals are increasing the background noise substantially it's not the amp. The just amplifies what it gets, so any additional 'noise' must be coming from the pedals, cables, guitar - something before the amp.

I'm using Fender 5' cable while I st near the amp and a Whirlwind 20' when I'm not and a couple of cheap patch leads, I don't generally use much in the way of effects tbh. In the past I got my overdrive sound straight from the amp.

I'm not saying there's nothing else wrong with it, but let's proceed logically.

 

[Firkwyte]

You can start by replacing all preamp tubes with masa tubes . The high and low Chanel’s are on v1 so if one is bad both are bad . You should also check the bias on the power tubes . Is the amp modded

The new power tubes were biased when fitted. It's a 1987 model and a small ancillary circuit was removed as it's not in the earlier models. The tech consulted directly with someone at Marshall before proceeding on that.
Would there be any advantage to using a Mullard valve over a Mesa for V1? I couldn't afford to replace the lot at almost £90 a pop but I could do a single and use mesa for the others

 

[PelliX]

The new power tubes were biased when fitted. It's a 1987 model and a small ancillary circuit was removed as it's not in the earlier models. The tech consulted directly with someone at Marshall before proceeding on that.
Would there be any advantage to using a Mullard valve over a Mesa for V1? I couldn't afford to replace the lot at almost £90 a pop but I could do a single and use mesa for the others

I'd hold back on that, frankly. Why not just get a brand new set of JJ's for a couple of tenners? Best case you like 'em, worst case you have spares for testing that were cheap. I don't know about your tech, but if I'd serviced an amp and someone had complaints like you do afterwards, I'd offer to at least put in and test with other valves for free.

I'm using Fender 5' cable while I st near the amp and a Whirlwind 20' when I'm not and a couple of cheap patch leads, I don't generally use much in the way of effects tbh. In the past I got my overdrive sound straight from the amp.

We may have crossed threads; I'm not saying it's the cable - I'm saying that your best guitar, cable and amp will have a level of noise. The more you add in front, the more noise you will often get. That's not the amp's fault though - a noisy pedal for example is a noisy pedal. Eliminate possible causes and simplify the setup until you're positive something is wrong with what's left.

 

[Chris-in-LA]

Does the 4212 even have a clean channel? There’s only one input jack. The first channel should be a regular Marshall channel and the boost channel kicks in the diode distortion. The regular 50 watter without the boost channel is capable of getting plenty of distortion. Your amp should not sound woolly. You should have plenty of high end and overdrive before you even kick in the boost channel. The amp sounds like it might be sick and it needs a thorough going over by a competent tech.

 

[Firkwyte]

I'd hold back on that, frankly. Why not just get a brand new set of JJ's for a couple of tenners? Best case you like 'em, worst case you have spares for testing that were cheap. I don't know about your tech, but if I'd serviced an amp and someone had complaints like you do afterwards, I'd offer to at least put in and test with other valves for free.



We may have crossed threads; I'm not saying it's the cable - I'm saying that your best guitar, cable and amp will have a level of noise. The more you add in front, the more noise you will often get. That's not the amp's fault though - a noisy pedal for example is a noisy pedal. Eliminate possible causes and simplify the setup until you're positive something is wrong with what's left.

Yes sorry my fault, I'm still getting used to the way this forum works, I'm a social media noob so my apologies for that. Anyway yes I get what you're saying. The noise is worse when I play the LP that has unpotted pickups in it, but they're coming out for a set of SDs very soon now. I play the LP the most at the moment for sure

 

[Firkwyte]

Does the 4212 even have a clean channel? There’s only one input jack. The first channel should be a regular Marshall channel and the boost channel kicks in the diode distortion. The regular 50 watter without the boost channel is capable of getting plenty of distortion. Your amp should not sound woolly. You should have plenty of high end and overdrive before you even kick in the boost channel. The amp sounds like it might be sick and it needs a thorough going over by a competent tech.

The 'clean' channel breaks up a fair bit when the gain is turned up but it lacks an brightness. Maybe I need to get a graphic pedal as there's only a Treble & Bass control on that channel and even with the treble up to 10 and the bass at just before mid-day it's woolly. The boost channel has decent overdrive but it's not a patch on the 100W model I once owned

 

[Firkwyte]

I'd hold back on that, frankly. Why not just get a brand new set of JJ's for a couple of tenners? Best case you like 'em, worst case you have spares for testing that were cheap. I don't know about your tech, but if I'd serviced an amp and someone had complaints like you do afterwards, I'd offer to at least put in and test with other valves for free.

Oh OK I've got 4 spare 12AX7s from my Mesa Studio .22+ that were swapped out - one of then is an Electro-Harmonix, I gues I could try that, the others are unbrandedd but maybe I could try them. Must say the little Mesa sounds much improved since I swapped out that assortment off odds & ends though


We may have crossed threads; I'm not saying it's the cable - I'm saying that your best guitar, cable and amp will have a level of noise. The more you add in front, the more noise you will often get. That's not the amp's fault though - a noisy pedal for example is a noisy pedal. Eliminate possible causes and simplify the setup until you're positive something is wrong with what's left.

 

[Leonard Neemoil]

I wouldn't use the odd ball tubes that didn't sound good in the Mesa to test in the Marshall.

If you really don't want to buy some JJs then take the GOOD tubes from the Mesa to test the Marshall.

I'd swap all of the pre amp tube at once. If it sounds good with the Mesa pre tubes, I'd just order a new set for it rather than cycle through trying to find a bad tube or two.

 

[Crikey]

I have the 4211 version 100 watt
Lead channel is fing awesome clean channel is too

clean every input jack twice. Footswitch/Guitar/ speaker/ effect

tighten the nut on footswitch jack

see if that helps

oh, and use different speaker cabinet to test

 

[Jethro Rocker]

I have the 4211 version 100 watt
Lead channel is fing awesome clean channel is too

clean every input jack twice. Footswitch/Guitar/ speaker/ effect

tighten the nut on footswitch jack

see if that helps

oh, and use different speaker cabinet to test

Yeah worth a shot! Clean fx loop jacks too maybe.

The 'clean' channel breaks up a fair bit when the gain is turned up but it lacks an brightness. Maybe I need to get a graphic pedal as there's only a Treble & Bass control on that channel and even with the treble up to 10 and the bass at just before mid-day it's woolly. The boost channel has decent overdrive but it's not a patch on the 100W model I once owned

I tried kne of those once, that series. The Presence control is preset internally very high, it should be beyond bright. Something not right at all that way. Try the pretubes first. It should not sound like that, and while an EQ can be really nice, shouldn't be required.
I forgot, as mentioned above, diode clipping kicks in on the lead channel. Possibly there is an issue with that circuit.

 

[Crikey]

Oh one last thing
The amp should be loud as f%#k when master volume is moved from .5 to nearly 1.2
Beyond 4 or 5 it just will be murky but loud

 

[Mitchell Pearrow]

@Firkwyte


To The Forum
Sorry to hear that your amp is malfunctioning, I do hope you get it sorted out !!
Cheers
Mitch

 

[steveb63]

Hmmm hard to say from just that description.
Firstly tech is nuts, you don't get an amp like that to run the clean channel. Ridiculous. He may well have put something different for a preamp tube in V1, I would check. That does not sound overly reputable to me. Did he check all the preamp tubes?
Generally There is no point in blindly putting Mesa pretubes in, for example, Mesa tubes are probably made by JJs at this point which may well be stock Marshall tubes as well.
Considering it's age, it may have very good preamp tubes and it may have weak ones. I would change out the first 2 preamp tubes with new known good ones and see it helps your problem first. Clean channel should get ice pick highs as required.
Past that I am clueless.

Caution sarcasm ahead......

The tech did him a favor, got rid of those nasty old Mullard tubes for him, and put in some easily available nice new production tubes.

Why, I'd bet the tech even disposed of those old nasty tubes, since they might be of envromental concern he probably did the guy a favor and disposed of them properly.

Sorry, but I have heard of similar things happening, especially to guys just learning about their new amps.

Good luck o.p., that amp should sound great, the dirty channel is why peple love those things. Time to investigate further, lots to learn right here with the search function.

Congratulations, when you have that figgered out think you will grow to love that amp.

P.S. I do know that amp didn't ship with Mullards- I'm just a smart donkey.

 

[jimmyo]

As it’s a combo have you had the chance to try it into a cab with different speakers? Anything from a stock 1960 through something with V30s or greenbacks can really change or enhance the tone an amp delivers.

If you can find somewhere you can really crank that bad boy up on the OD channel through a 4x12 it should sound like Thor’s hammer

 

[Jethro Rocker]

Caution sarcasm ahead......

The tech did him a favor, got rid of those nasty old Mullard tubes for him, and put in some easily available nice new production tubes.

Why, I'd bet the tech even disposed of those old nasty tubes, since they might be of envromental concern he probably did the guy a favor and disposed of them properly.

Sorry, but I have heard of similar things happening, especially to guys just learning about their new amps.

Good luck o.p., that amp should sound great, the dirty channel is why peple love those things. Time to investigate further, lots to learn right here with the search function.

Congratulations, when you have that figgered out think you will grow to love that amp.

P.S. I do know that amp didn't ship with Mullards- I'm just a smart donkey.

Could have EI smooth plate maybe, depending on year, my 1983 2203 came with Polamp (RFT!) pre tubes. With any luck whatever was in there still is except V1.