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Unread 04-19-2011, 09:41 PM   #1 (permalink)
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Marshall Jcm600

Hey guys new here 1st Marshall in a long time, yeah I know,, Long time a coming.

Anyway's I just bought a 1998 Marshall Jcm600 1x12 bone stock, original speaker and tubes.

What are your thoughts on tubes in these? If there working should I not go with the addage that new tube's may bring new life to the amp. SHould I keep them original tubes until they start failing.

Second Can somebody point me to some directions on how to bias this girl, I have looked around but the amp doesn't seem to have a huge following and not much information. I need to know where the bias pot is and what do people usually bias these jcm 600's too?

I love the sound, currently I have a peavey delta blues with upgraded tubes and speakers,it's a 2x10 and the marshall's 1x12 heritage just sound's so much better.

I play rock, classic page rock,hendrix,Kossoff etc.. The clean channel on this amp is fantastic, make's my delta blues sound like it has a blanket over it,hence why I traded a faded brown sg for this marshall, it's mint and all original with beautiful leather cover in Flaming red no doubt.

If anyone can spare a minute to help, I would appreciate it so much. I'm going to enjoy the amp right now, but I would like to know what tube's and bias instructions for when I need to. Look's like marshall branded tubes installed right now,, I just want the amp to sound the best it can;.


I don't think this amp is cheap at all and in fact I think they stopped making it because it was costing them to much to make an amp like this in England and make profits against competitors. I mean this thing is rock solid and for what I play sound's beast and the beautiful.

Thanks guys
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Unread 04-19-2011, 09:59 PM   #2 (permalink)
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Re: Marshall Jcm600

Considering what you're playing you might go with a low power / 70% tube in v1 to tame some of the gain characteristics down this way you can crank the preamp. Paul use to run his gear WIDE ass open to get his tones, as did Jimi so it wouldn't hurt.. other guys will chime in with more to bring to the table than me... but yea, definitely a philips 5751 or whatever it is in v1
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Unread 04-19-2011, 10:06 PM   #3 (permalink)
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Re: Marshall Jcm600

cool,cool taking notes. Thanks ReignMan. I do like 5751's, but I'm digging the gain on this amp. I have a feeling that my strat might get neglected unless the rumplestiltskin pup's I ordered are the bomb bigity. I just cannot get enough of the les paul through the marshall tone.

I am thoroughly digging the clean's here as well and the seperate reverbs. Also it is kick ass that the amp has serial and parallel fx onboard. I will probably never use parallel fx but choices are great.
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Unread 04-19-2011, 10:18 PM   #4 (permalink)
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Re: Marshall Jcm600

I would reccomend changing the tubes. They are pretty old if they are original. I had a JTM 60 head which is pretty close to what you got there. Good tones. I do know they were prone to overheat. But they sound pretty damn good.
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Unread 04-19-2011, 10:38 PM   #5 (permalink)
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Re: Marshall Jcm600

Yeah this amp doesn't overheat, I know the guy I got it from and he is local musician and gigged it 3/4 times a week,religously. Never a problem, I think what I'll do is keep asking what some good el34's are and see how they sound, I can alway's put original's back in and use new one's for backup's. I know good pre amp tubes, just never had any experience with 34's, just 84's,6v6s,6l6's and um yeah that's it.

i have to figure out the bias procedure first as well, because Ihave always biased my own amps and i know that's important to do when swithing p.tubes.
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Unread 04-20-2011, 12:14 AM   #6 (permalink)
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Re: Marshall Jcm600

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Originally Posted by gadgetfreak View Post
Yeah this amp doesn't overheat, I know the guy I got it from and he is local musician and gigged it 3/4 times a week,religously. Never a problem, I think what I'll do is keep asking what some good el34's are and see how they sound, I can alway's put original's back in and use new one's for backup's. I know good pre amp tubes, just never had any experience with 34's, just 84's,6v6s,6l6's and um yeah that's it.

i have to figure out the bias procedure first as well, because Ihave always biased my own amps and i know that's important to do when swithing p.tubes.
Youtube can be your friend, in addition plenty of guys have made threads etc, pull em up!
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Unread 04-20-2011, 12:24 AM   #7 (permalink)
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Re: Marshall Jcm600

I don't have any tube recomendation but welcome to the forum!
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Unread 04-20-2011, 02:13 AM   #8 (permalink)
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Re: Marshall Jcm600

decent gain level nos tubes imo are RCA 7025's. you can get metal gain levels with them but, they're rich and have a hint of chime so they do cleans really well too. i'd go with those in V1&V2. you'll get a thicker singing tone with some good crunch and even hi gain out of those.
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Unread 04-20-2011, 02:15 AM   #9 (permalink)
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Re: Marshall Jcm600

Quote:
Originally Posted by ReiGnMaN View Post
Youtube can be your friend, in addition plenty of guys have made threads etc, pull em up!
youtube's what launched my legitimate career. without it i'd not have started this session work nor found bands that want me to tour with them etc. it's really useful to get in the know of things in the bus apparently.
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Unread 04-20-2011, 09:38 PM   #10 (permalink)
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Re: Marshall Jcm600

Yeah bro, cool amp..............I've got one of those baby's just for pre gig warm up/ guitar repairs & it EFFIN screams. Even though you don't feel the need, keep a small fan on it so it doesn't overheat.


The bias pot on a JCM600 is located on the end of the chassis on the power tranny side.....sort of difficult to get to.


check this link on previous thread
jcm600 bias pot symbol
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Unread 04-20-2011, 09:39 PM   #11 (permalink)
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Re: Marshall Jcm600

Might as well read all of these just to get to know your amp

Marshall Amp Forum - Search Results
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Unread 04-30-2011, 06:25 PM   #12 (permalink)
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Re: Marshall Jcm600

LibertyMachine Thanks for the links. I can't keep up with my post's and nothing remind's me when somebody replies. Peace
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Unread 05-01-2011, 08:15 AM   #13 (permalink)
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Re: Marshall Jcm600

Quote:
Originally Posted by gadgetfreak View Post
LibertyMachine Thanks for the links. I can't keep up with my post's and nothing remind's me when somebody replies. Peace
You have to go into your preferences and set it to be notified when someone replies to your posts.
It's not turned on by default. (I think it should be).

Took me about a year to figure it out.
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Unread 05-11-2011, 10:06 PM   #14 (permalink)
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Re: Marshall Jcm600

Just wanted to update, I just finished bias'ng amp. I ended up going with Ruby el 34bstr's, nice big meaty tube compared to stock svetlana's, the svetlana's were old,original tubes but even the newer one's I tried had no bass at all, these Ruby's sound great. Kinda wish I sprung for the winged =c='s to hear the difference but to my ear these sound great.

I went with a tungsol in v1
pentalabs v2
pentalabs v3
Sovtek Lps v4

THey sound good, won't really know until I can crank em up but right off the bat my rattle is gone and defintion has come back to 31 willow st..

It's not as bad to bias this amp as some folks have commented on, Let me take that back, maybe I have always had crappy amps to bias so to me it wasn't that bad, the bias pot was right at the end of chassis so nothing in the way, it stand's vertical and very easy to get too. I did however learn that marshall's are very sensitive, I turned it maybe halfway not even and my dmm went up to 190.3mv and the original tube completely turned into a glow rod, I turned it back real fast. Pretty hairy there but once I realized the amount to turn trim pot it was fine.

I am going to play amp for awhile and listen to what she sound's like and if I feel the need I may have the clipping diode mod done to her. I could go for some more natural sounding tube break up/gain but I will wait a bit.


I had just aquired this amp and it sounded ok but I think the original tubes went from some life to next to nothing really fast and original owner heard this happening and dumped it. I'm happy so far, one thing I can attest to is with the jcm600 there is a vent in the top, it helps get rid of heat. I've had no problems and I play for hours a day. also when inside the chassis nothing looked melted or off. Only time will tell, but I am stoked with this amp and cannot wait till get out of work tommorrow and crank her ass up.
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Unread 01-08-2014, 01:56 PM   #15 (permalink)
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Re: Marshall Jcm600

For the records, biasing point for the jcm601
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