Marshall JCM 900 Model 2100

In this video we take a look at another JCM 900 the model 2100. I mention the common issues related to most of the 900 heads, and correct someone else's work. We also talk about some tube rolling.

[@MisterFruitbowl]

I got 3 2100s and 1 2100 SL-X. Love ‘em to bits!

[@guitarc.p.r.9675]

Definitely my favorite 900 series amp.

[@guitarc.p.r.9675]

I must apologize to the the gentleman ( I believe his name was Bill ) Who posted a very nice comment on the results of modding his 4500 per my instructions. Due to a glitch and an unresponsive page his comment was lost. It is a shame because it was a a very good one and I appreciated it. I approve and answer most comments, unfortunately occasionally one goes MIA. So hopefully he will see this and know that I thank him.

[@luthiervandros]

Great video. Those impedance and high low switches often burn up and become resistors.

[@varanidfury8634]

I have that amp it’s a beast. It’s the one JCM 900 that does not have diode clipping. I bought it from guitar Center in San Francisco when I was 16 I am 47 now and I refuse to sell it. I also have a JCM 2000 DSL 100 H that’s made in America. I love it as well but I will not sell the 900 because the 2100 series is the only good jcm 900 in my opinion because it has no diet clipping. They actually added an extra tube for that purpose.

[@guitarc.p.r.9675]

Thanks for checking out the video. If I have a favorite 900 this would be it. This is probably what I consider to be the last "real" Marshall. The big differences here are the two gain stages in your amp are actually tubes and not ICs. From the tone stack driver on, sans reverb and a tube stage in the loop return circuit the rest of the amp is the same including the dual master volumes. I do have to mention though that there is a bridge rectifier (BR-1) and 1n4007 circuit between the preamp volume and tone stack driver tube for clipping purposes, as in the Dual reverb models. It just is not as prominent as in the 25xx-45xx models that have the Led clips in the gain channel as well. Thanks again for watching.

[@deanallen927]

It can be troublesome in that there are three different schematics for these things. I had the 50 watt version 2500 Mk III. I undid the first two sets of diodes and it really sounded nicer, adding a 5157 helped. I didn't feel skilled enough to take out the very small bridge rec further down, also attached to the signal path but it did improve. I also had to mod the bias to get the voltage way down, a different problem than the 100 watt usually has. Also changed the screen and grid resistors to normal Marshall values and types. Ended up liking the amp.

[@guitarc.p.r.9675]

Careful man.... the 900 police will call you on replacing the grid resistors.... they have me. Heaven forbid you mess with the sanctity of the righteous 900. Obviously, they have me confused with someone who cares about their opinion... :)

[@ryankozak6874]

I just did a full recap on my JCM900 mk3 100w head. It's actually tighter, louder, and overall more crisp. Have much better control of the volume and it super responsive now.

[@guitarc.p.r.9675]

Caps are the most important part of and amp, second to transformers. I have preached this for years, especially in marshalls. One passed amp guru insisted on changing Marshall caps every 10 yrs. I agree. People do not realize that is is a slow degradation of the power supply that feeds the amp. The factors you mention in your comment slowly fade and is un-noticed. I have had numerous customers ask what "Mod" I did to their amp. Usually my answer is no mod, just new quality caps. That is the way your amp sounded new. Thanks for watching and commenting. It is always pleasant to see a positive comment on the Marshall videos.

[@ryankozak6874]

@Guitar C.P.R. thx. Not to mention I maybe paid like 25 dollars with shipping.. its super easy to do

[@guitarc.p.r.9675]

You did replace the bias feed cap, bias caps and pre-amp supply caps, Right?

[@ryankozak6874]

@@guitarc.p.r.9675 everything

[@ryankozak6874]

@@guitarc.p.r.9675 I just did everything in one fell swoop

[@christianboddum8783]

Is it the sensitivity side that introduces diode clipping? I know there are things you need to know about these 900s. There is also something about how you hit the phase inverter, rather than the diodes to get a more natural clipping, but I can't remember anymore. Any info or tips?

[@guitarc.p.r.9675]

No, the diode clipping is always in the circuit. The sensitivity is another name for a gain control and follows the 1st gain stage. The preamp volume is after the second stage and the diodes connect directly to the output of it on the way to the tone stack driver. Hope that clears t up a bit. No tips except play the amp and get to know it. Thanks for watching!

[@tractordirt]

Very helpful video…thanks for posting! I just bought a JCM900 mkiii, and has a couple issues. The sound fades and cuts out occasionally. Also, the channels won’t switch…stuck on B. Otherwise, aside from some noise, it sounds really good. Can you give me any ballpark figure on what going through the amp like you did might set me back? Probably needs filter caps as well.

[@guitarc.p.r.9675]

Sorry, I cannot give you a figure. Every case varies and there are too many variables.

[@sjgreaves]

Those grid resistors are interesting... I took a look online and found the issue 1 and issue 7 schematics seem to be drawn as I would have expected (and as you wired them) just the issue 10 and above schematics are "wrong".

[@guitarc.p.r.9675]

I have seen it on several models including the very first (oldest) 900 I ever worked on. Regardless of what the schematics say, the amps are wired that way.

[@timcees]

I bought one of these used for $350 around 1996

[@ghostface_grilla1155]

Another great video!

[@guitarc.p.r.9675]

Thanks again!

[@anthonymazzola767]

Nice work! Do you recommend replacing the bias feed capacitor on the 900 SLX? If so, What value and temp? Thanks.

[@guitarc.p.r.9675]

Replace the bias cap in ANY 900. The spec is the same as in the video .047uf 600/630v. As I said in the video I prefer the Xicon caps because they fit the board.

[@anthonymazzola767]

@@guitarc.p.r.9675 Thank you.

[@michaellrakes5521]

Is the 2100 MK3 series? Reason I ask, is I have a 1993 2500 SL-X series, which was the next step from the MK3 and the only difference apparently was the MK3 had diode clipping where as the SL-X added a 4th ECC83 to create the extra gain stage. Other than that, basically identical. In fact, that amp is currently dead in the water as of the last 2 years. Something went terribly wrong and blew the mains fuse one day at random Riff. I had someone nearby attempt to "fix" it and I think they did more damage honestly. The heater circuit has too much current passing through it and fried one of the power sockets, while they tried to repair the other one poorly. So long story short, perhaps you could work your magic on it sometime?

[@guitarc.p.r.9675]

I will bet one of the outputs had a heater to screen short.

[@AndyK.23]

What happened with the SL-X is, they added a preamp tube (which increased the current), but didn't upgrade the bridge rectifier (BR2). This eventually causes the BR2 to burn up, taking other caps with it. Check yours and see if it looks toasty.

[@deanallen927]

If I'd kept mine I'd have shortened all those leads on those first two tubes. Too much extra wire.

[@guitarc.p.r.9675]

Yes, Marshall can get sloppy with wire, and lead dressing is important.

[@jeffallen3382]

Never understood why there is so much hate for the JCM900 series?

[@guitarc.p.r.9675]

Guys that grew up with JMP's and 800s just don't care for them. Unfortunately sound wise and construction is lacking. I always felt this was the point Marshall started heading south. They are useable amps but the 4500 series was a bit cheesy. This 2100 series is actually more true to the roots, but for those who are just looking for that little bit more gain, and more modern voicing. This amp is built for pure Rock & Roll. Of the 900's it would be my choice...... after doing some work and pulling some stuff out. Thank you for viewing regularly.

[@jeffallen3382]

@@guitarc.p.r.9675 your 4500 video from way back helped me repair the bias control box cap that failed. I should replace the caps and fix the series grid resistors. It's all stock and from 91 or so. It's time they get fixed. Thanks for all the great videos you put out.

[@guitarc.p.r.9675]

Thank you much appreciated.

[@randymatheny8621]

Have you ever made a guitar from scratch

[@guitarc.p.r.9675]

I built guitars from 1976 through 1993. In fact there are a few that reappeared after a few years and have made it onto this channel. Look for Phil, Blue Boy, and a couple memory lane clips.

[@zbaby82]

I'd like to have a 50 watt version of this amp.

[@guitarc.p.r.9675]

Exactly! As I recall in various head and combo models...that would be models 2500,2501, 2502, 4500, 4501, and 4502. Serious Rock & Roll amp.

[@sjgreaves]

I have one I picked up very cheaply because someone had had it modded with a mod he found online to make it sound like an 800... it didn't but at least the mod was done by a pro so no damage and most of the original components were still in it so it was easy to revert to stock. Don't be fooled, the 50s are almost as loud as the 100s (that is generally the case anyway). I like them for what they do...

[@shredding51]

Every 900 i've ever owned had a hum

[@guitarc.p.r.9675]

Then they were not right.

[@jeffallen3382]

My 4500 JCM900 is dead quiet! I've never had a noise out of mine and it sits next to my pc and a 90 gallon fish tank with all kinds of electrical things running. From the filters, power heads, florescent lights, and air bubblers.