I was wondering if anyone here have any experience with the Marshall JCM900 combos? I'm in the market for a high gain combo and has been offered one of these. I believe it's a 50 watt 2501 mk3.
Do they have enough gain to play heavy and black metal on its own (without any pedals)?

needs pedals... gorath said the digitech bad monkey did the trick, which is an el cheapo pedal, and especially cheap used/off ebay.

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Thanks, I'll check out the bad monkey then. Do you have any examples of bands using the 900? I would like to get a better idea of the tones it is capable of producing.

cannibal corpse on Tomb of the Mutilated, and albums beforehand.
... some old morbid angel... ask Soeru, he knows that detail.
Weezer... (heheheh)
Kiss...
Alice Cooper...

i dunno... it has the potential to be a pretty thrashy amp...

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i've just bought a jcm900 50 watt (it's a head though) and i think it sounds pretty damn hostile.

the tubes i it are pretty old so my guess is it would sound even better retubed. i play it through a mxr-dimebag distortion and its a damn good old school sound i have now. good luck with it, and whatever sound you're looking for, im sure the jcm can pull it off

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Bands that use a 900? Well not the particular 1x12 model, but as far as the heads go:

Morbid Angel(all records since day 1, and they still use em to this day).
Obituary.
Napalm Death(used to live and on some old records).
Decapitated(only their first album and live I believe).
Assloads of thrash and plain ol heavy metal bands.

It's a great amp on it's own, but to get really brewtal with it you're going to want some heavy overdrive pushing the front end and/or some distortion unit like a good ol MXR, Proco Rat, Big Muff pedal, etc. but those are generally more suitable if you want loose-y crunchy grinds as opposed to tight all-out mayhem a big Overdrive boost will give. Also give it new tubes.

Someone else bought the 900 2x12 combo, said the cab was made out of thin particle board and had poor bass response. Modding the cab will help, but if you want a JCM900 I suggest nabbing it in 50W head-cab combo, won't cost much more if at all, and will sound a lot better if you avoid Marshall's cutting corners on their combos.

Or if you need a combo format no matter what, I suggest looking for something else, Marshall makes great ampheads and cabs but I've never heard many good things about their combo amps. Probably much better stuff out there for the price.

Take a look at these high gain tube 1x12 combos:
Engl Thunder 1x12 - 50W, lots of gain, 700$ ish?
Ampeg VL-503(if you can find it) - 400-700$ ish tops. Lee Jackson designed, assloads of gain and features, like a built in attenuator, tube driven FX loop, DI outs, etc.. It's oversized and weighs a fucking ton though.
Peavey Bravo 112 - 30W all tube, Marshall on steroids sound with a shitload of gain. 200-300$.
Peavey Ultra 112 - Predecessor to the XXX, ultra br00t3l modern high gain, 250-350$
Crate Stealth GT 50 - 200-350$. Lee Jackson designed, great gain although too thin sounding, will require new tubes and perhaps a darker speaker.
Crate BV-60 Blue Voodoo - 200-300$ Great bang-for-the-buck high gain combo, like the Stealth but less trebley sounding(but also less reliable I hear).

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I have a 100watt JCM900 combo, sounds great, obviously it sounds better as you turn it up. When I'm playing at bedroom levels I use a RAT in front of it to boost it but I'm getting to really like the distortion on it's own without a boost. Only problem I have is it gets very muddy with lower tunings, my v with an SH-8 tuned in Bb gets very muddy indeed, however, it sounds great from E - D, very clear, nice distortion.

Yeah I recently bought the 2x12 4502 model and it needed some work to get what I wanted but it has pretty awesome tone now. Not loads of gain but enough for 80's/90's thrash and black metal etc. My friend has the exact model you are looking at (1x12 2501) and it sounds very different though, so you'd need to change some bits. For a really tight crisp sound I'd recommend Electro-Harmonix tubes throughout. To get it where I wanted I replaced the speakers with a Vintage 30 and a G12k-100 (get the V30 for a 1x12) and boosted it with the Digitech Bad Monkey. The Monkey is totally transparent and is literally just like adding another gain stage to your distorted channel. Set it with the Gain at 0 and the Level all the way up and adjust the bass/treble to suit. It will never sound as bassy as a 4x12 but it still sounds pretty killer for leads (incredible sustain and clarity) and chug rhythms come out pretty good too.

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Thanks, that's rather useful information. How would you describe the tone of your friends 112 combo in comparison to your 212?

I finally decided upon buying the jcm. I'm eagerly awaiting it's arrival. I just wanted to thank you all for your help.

I reckon you'll like it, though it may very well need a boost, they do sound great though!

My Friends 2501 is more warm sounding than mine and the gain isn't as razor sharp, leans slightly towards fuzz. I'd bet though a valve swap would change that completely. Like I said Electro Harmonix are awesome in this amp. Feel free to PM me in the future with any questions.

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Thanks. How many preamp tubes are there in this amp? I would assume changing the preamp tubes would change the tone more than changing the poweramp tubes?

Yes definitely. There are only 3 preamp tubes in the 2501, so its not too expensive to do. My exact purchases were the standard 12AX7EH from hotroxuk.com at about 8 pounds each. Not sure where you're from but they should be pretty cheap wherever. You can also buy the Gold version 12AX7EH but tbh I'd only bother with this for the V1 position. Mine sounds great with 3 standard ones.

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Yeah I had my 100 watt JCM 900 4100 (year 1990) re-tubed and biased hot, with Mullard reissue valves and a Harma STR 270 preamp valve for V1. (Awesome gain compared to the stock valves, in fact it's one of the highest gain ECC83s availabe) It sounds pretty brutal, I have a clip of it on youtube, it's called ''JCM 900 Sound Test No Pedals''.