Diagnosing & Repairing Marshall JCM-900 100W Hi-Gain Dual Reverb 4101
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- Опубліковано 18 жов 2024
- Here's a model 4101 Marshall 112 combo with 5881 power tubes. This amp had red plating EL34 output tubes when I got it. The fault was found to be with the C15 capacitor in the bias supply. Also needed a changed Master Volume pot on Channel 1. While I was at it, I went ahead and moved the pots to the chassis and ran wires to them (a reliability improvement). I also demo the tone about halfway into the video before I realized I needed to change a pot.
Yo Brother!
I'm relatively new to watching your videos and am thoroughly enjoying them!
I'm a permanently disabled Class A I.B.E.W. Union Electrician. 28 years into my career I was remodeling a section of Space Mountain at Disneyland in Anaheim, California and fell ending my ability to work at what I LOVED doing for so many years. My whole life changes in an instant.
Although I have an extensive background in Electricity, I have really never pursued "Electronics". Consequently I know very little about the subject.
The more I watch you work on amps it's just all really starting to Click in a huge way!!!
I Thank YOU for my new found interest!
I have a couple of amps that I was going to send out to have repaired...but what the Heck...I'm going to tear into them myself!
Thanx again for all you do and helping me to realize that here's something I can do in my limited capacities!
Best to You and Your Beautiful Family!
Ed
Loved this one as I have a 50w version of this exact amp (4501). It's an absolute beauty and criminally underrated because of all the people fellating the 800. Channel A is a dream.
Had one as well, and wish I still had it.
just got one for free. Not sure if its in working condition just yet.
lucky you
@@Danh103663 same
I have a JCM 900 4500 50w dual reverb head. I love it. Very loud w my Slash signature 1960 slant cab. Got both used as a 1/2 stack for $1300 22 + year ago. Best $ I ever spent. Add TS9 tube screamer and faces start melting at will.
Brad I just bought one of these heads for 130bux. It's a barn find. Been sitting nine years.it will be here in a few days I'm stoked.i love these.
Cool. Congratulations! Make a video.
I had a 2x12 version of this amp and loved it. Was very sad to let it go when I moved to Australia
I had a JCM 900 half stack, the dirty channel was a workhorse, but the clean channel always sounded thin, so I ran a SGX 2000 rack mount through the send return jacks.
Great video, home boy. You never cease to amaze me.
+Lindsey James Williams Amazed is better than repulsed. I'll take it! :P
RE loads.
I purchased 4ea 16 ohm 50 watt Arcol resistors from Mouser for my 8 ohm loads and series/ paralleled them to make 8 ohm 200 watt loads and mounted on an old heatsink.
I made 2ea of these so i could series or parallel them for any other load i may need.
For higher power needs as in PA power amps, i just use a couple of pressing type irons paralleled with the thermostats bypassed.
Works very well for relatively cheap.
GAIN AND SUSTAIN .....A FEW OF MY FAVORITE THINGS ...hve not played in years but my ax is still playing the last note ...lol
I ran into the same issue putting a JCM900 head back into original condition. Someone had modded it to take 6L6s. That was not factory - you could see it. I put it back and it sounds great with an EVH greenback cab. My first Marshall. I am 59 years old. I would like to know where you got the correct schematic. I couldn't find it.
I built a Valco 1624T from scratch. Love that amp. Put in the original speaker. Lordy - it doesn't get any better!
Cool... and definitely, having the tube sockets chassis-mounted helps the tubes to dissipate heat through their bases way better..... those power output tubes definitely get HOT! :-)
To keep from burning traces. Using a High quality solder wick will soak up the solder and act as a heat sink to keep as much heat off the circuit board and traces as possible.
I have one of these! It's my favorite amp.
Would guitar amplifiers sound a lot less noisier if manufacturers started using metal film resistors?
5881 drawing: the final grids are misfed, the second grid on each side sees the signal through an extra 1k5 resistor that comes AFTER the 1k5 feeding the first grid, these 2 resistors are in series for the second tube's grid, out of the PI, the left grid sees 1k5, the right 3k, so one of each pair of the output tubes is being driven twice as hard on the grid as its mate... one will fail before the other, right?
el34 drawing: The grids are all fed the same, each grid fed through a dedicated 1k5 and a 2k2 in series for each grid. All grids see 3k7 out of the PI....
No offence is intended what so ever, But your videos are incredibly informative yet incredibly slowly paced. So what I tend to do on your video is run them at 1.5 speed. I wanted to mention it more for the benefit of your viewers in case they find your video's too long or slow they might get more enjoyment from them and hopefully get you more video views.
You're right, they can be slow at times.
+The Guitologist They can be slow, but I'm personally against the craze of speeding up everything. I don't know why, but channels like this channel, uncle doug, carlsons lab etc, although slow at times, you really learn something.
I used to watch everything at 1,25x but have stopped doing that because the net time spent was probably more due to the need of pausing the video and reflect from time to time :)
I'm for slow! :D
I think you'll notice on my channel if you watch enough of my older and new videos, I've experimented with a little of both slow-paced stuff giving every minute detail and more edited down stuff where I try to cut to the important bits. I personally like and dislike each approach for different reasons, but ultimately, anything that means less editing for me usually wins out. :)
+The Guitologist Maybe, have mostly watch newer stuff. Lots of planning then one-take shot videos would be the goal if I did videos for people :) My channel is mostly for myself lol
I received as message saying there was a reply to my original message but I don't see it... Anyway, the main reason I shared the above comment was not to insult the Guitologist. On the contrary. I love his videos and hope others do to. My comment was written in the hopes that if other people would otherwise like his videos but found them too slow for their attention level, I wanted them to try this trick of speeding them up, thus causing them to enjoy the videos more and get the guy more views which I hope translates into more money for his excellent content... I hope people read this before calling me an ass hole or the like.
Had to use another 900 a friend had that was factory. The R28 vs R30 was throwing me off. But like you I got past that real quick once I had the other amp. An amp for a schematic. If you can point me in the right direction I would appreciate it.
Hey Brad, love your videos. I'm not an EE, but I do a lot of my amp work - biasing and so forth, and I like the way you explain things. I had a general question: I have a '96 4100 head, which is supposed to come with 5881's, and someone has put Tung Sol (newer) small bottle 6L6 tubes in it. I know this amp came with EL34's and then the last two years, '95-'96, had 5881's. I looked at the schematic, and aside from changing that bias range resistor to get the bias in the right range, it looks like they changed some 5W 470 ohm screen resistors (?) to 2.2KOhm 5W for the EL34's. I've got some 2K 5W resistors. Is that close enough, or should I get some 2.2K? Thanks.
As I see the C15 is not in the bias supply circuit. It placed between the V3 anodes.
Didn't you confused with the numbers?
Any reasons why they change the biasing circuit for 5881 and EL34>? I bias circuit for these marshall amplifiers is done by measuring the current ( not the voltage ) so its some type of current mirror circuit or current comparator circuit to adjust the bias.
I have a question, could using the wrong rectifier tube cause a power tube to burn out? Example, I have a tube amp that called for a 5az4 rectifier tube and actually what I put in there was a 6x5, could this be responsible for to cause one of the power tubes to burn out? Thanks for any help on this. I know that there are suitable replacements on these type tubes but a 6x5 is never mentioned in the possible substitutes.
Killer double stops in your demo. Being that the bias voltage between the two schematics was pretty close do you think the tube swap could have caused the cap going bad?
It's got a decent reverb. I've never heard a Marshall amp played through. Not bad sounding at all.
try a marshall valvestate 2000 avt 275 clean and powerfull reverb and as filthy as you could want on the overdrive .try one.
Hey buddy why is it popping and clicking??? I have one and it has never been right. Could you help me fix it. Mine makes the same sound and then drops the volume.
Just repaired a 4502 and a 4102 recently.
Killer amp- love to have one
I have one for sale
Great video and nice playing!
Would it be safe to pull two power tubes on the 100 watt to bring it down to 50 watts if so any down side to doing this?
Hello I wonder what your labor cost is on your service. It scares me to buy the one I just bought
I have the JCM 800 And JCM 900 ..I mentioned before i haven't used my Tube Amps hardly at all since i bought my Marshall MG FX100 2X12 with Celestion speakers it came with in 2009...no need really to only rely on any Tube Amp anymore..first off their not reliable..the technology with the Solid State Amps the past 20 years simply remarkable..the first modeling Amp came out back in 1996 by Line6..since the past 22 years since the first modeling Amp they have become remarkable..and do everything a tube Amp does with much more reliability..and with out the hefty price tag..Solid State is the way to go..and it seems I'm Right because i see many musicians today Recording and playing live with Solid State Amps..i will not ever go back to Just using Tube Amps..Solid State does it all...
Great that you like your amp. Solid state or valve it’s how it sounds that matters. However there should not be anything fundamentally more or less reliable in a valve amp than a solid state one. The main reliability issues with amps seem to be connected with the quality of the build and the quality of the parts. Pots and sockets that are not properly supported can be found in either valve or solid state amps and cause problems. In some modern valve amps the tube sockets may only be supported by a circuit board and this is also not a good thing for reliability. The point is that a well built valve amp should be just as reliable as a solid state one.
Solid state sucks... The modeling amps just don't cut it for me.
I have the el34 version of this amp. I changed the pots. Now I wanted to change the basis caps. The value of the caps is .047/250v. Should I stay with that value or would it make sense to replace them with a larger voltage? Like .047/600v?
I don't see what harm would come from upping the voltage on the caps.
I used to have the 2x12 version of this amp and it was a beast. but way too loud. I got rid of it because there was nowhere in my home town that I could turn it up...
Do the pre amp tubes need to be biased to operate if so how is that done. There's a lot I don't remember I'm having to learn over again. Thanks for the help.
Preamp tubes don't need to be biased. Or more correctly, their bias is non-adjustable.
where do you get such good schematics from? Ive seen several websites with the schematics but the print quality can be hard to read especially when looking at the value of a component
This is a good source for Marshall schematics: www.thetubestore.com/Resources/Marshall-Schematics
Thanks, I'll check it out!
Great run through and repair video Brad. Off topic: Did the Lyle get sold? I hadn't heard back from you about it. If so, that's fine. If not, I may still be the buyer for it. Thanks.
+August Lyons Yes it did. Sorry, man.
+The Guitologist No worries. I have more than enough guitars already, yet, I want to buy more! lol
damn seems like all Marshall volume and gain posts go,my lead 12,and lead 20
my JCM900 sounds very low, even turn the mast at max. could you tell me the possible problem, many thanks. BTW, I insert the guitar into the Return jack, it's still very low
old tubes,cold bias
I have one of these that I would like to take all the pre amp crap out of. Is there a video out there on how to do this?
no,definetly not something a rookie can do or learn from youtube.you gotta know your shit 100%
@@trillrifaxegrindor4411 I slept at a Holiday Inn last night.
Well the amp has not worked at all for years. Totally dead. I took it to a tech and he worked on it and then said he can't find the problem. Its dead. So.. what do I have to lose really by disconnecting a the pots etc and trying to put it back together. I have done a few amp mods already.
I can't believe a company would mount sockets to a PCB, it's just trouble waiting to happen. For a couple dollars more all company's should have chassis-mounted sockets
Problem is, it probably would DOUBLE the price of the board because it would require a human to solder them in.
I would still rather have a 12 year old chinese boy solder off the board than a made in the USA on the board socket..... at least it'll be easy to fix later on.....same goes for pots. Or at the very very least make sure that board is rock solid stable and can't bend.
The tube sockets are mounted to the chassis not the pcb
i can have a fresh serviced 4101 for 650$ CAD.... can be good ?
Is that dual reverb controls for each of the channels?
Great video man ! I wonder if this is what's wrong with my original Carvin x100b ?
The X100B is a nice amp. I've owned several of those over the years. Did a lot of recording with them too at one point. Maybe when I begin accepting outside repairs again, you can send that one to me for repair...
Don't know why you're interested in those "box caps" in the coupling stages.
They're damn near indestructible.
All those electrolytics, especially the ones for filtering could stand an upgrade.
Don't overlook the 1000uF and 470uF radial cans on the preamp board.
And the two 10uF elcos. in the bias supple for sure!
is it this video or all dual reverb sound cocked-wha like this one? 'cause I'd like to get one...
Not sure what "cocked-wha" means. I guess I'm too old.
it is when you turn on the wha but instead of using it doing up-down with your feet, you leave the pedal in a spot position...in this way the wha stays and works only in a certain range of frequencies, like a filter if you want. Now the distortion of this amp in this video (and in some other to be honest) sounds a little bit that way: little bass and much high-mids with a transistor like tone too. I hope it sounds better in person, 'cause I'd like to buy one.
Something tells me that the variable wire-wound resistor you're using for a load may have its wattage rated at 150 ohms and a given current. When dialed down to as low as 8 ohms the wattage capability would be much less at the same current as the resistor is rated at (150 ohms). There are way less windings to dissipate the wattage/heat.
This is correct. This thing does get very hot, so I go easy on it. I have some other dummy loads coming so I can build a better one soon.
Is it possible to remove the amp from the cabinet and rackmount it?
No reason to do that. These heads and combos go for the same $.
What kind of fuses do I need?
Hi! Can you help me?
Can i turn my jcm 900 instó a jcm 800? Or get close ?
You just have to go diarea in the bias pot and put a booger on the cathode follower and finally replace the phase inverter wires with pubes and your done
take out the part of the circuit with the diode clipping, get some of the types of transformers that are in 800s, etc.
Buy an 800.
Hi,
This is a great video and great amp, I have one exactly the same model with the 5881 tubes. I was wondering if you can tell me where did you download the service manual and the schematics. Mine needs some work to remove some noise (maybe pots or some solder joints).
Thanks!
You should order some new pots if you can afford it and just move the pots from the board to the chassis and run wires. You'll never have that same problem.
That is not a bad idea, but a lot of work :( specially because I don't have a workbench! thanks! Can you help me with the schematics?
I just googled it. Not sure where I found them now.
ok, thanks. I've found some for the 900 but from your video the ones you have seem more accurate. I'll keep looking.
what is burning the traces?
Whose ear is appearing at 14:35 ? ;-)
juicy yo!
+wefysan58 Once I got that popping to stop after replacing that offending pot, it sounded great. Cool combo...TONS of power for its size.
I have the 4100 head and a 4102 combo ...yummy
Hello, I have a JCM 900 100w 2x12 dual reverb - I'm currently using the amp on 50watts via selector switch on the back. Please would you be so kind to tell me which impedance setting I should select. The speakers are 2 x 16ohms - what should the selector switch be set to, 8ohms or 4(16)ohms??
I dont know if the speakers are wired parallel or in series, although it will be standard wiring from the factory.
Many thanks in advance
The total impedance for two 16 ohm speakers will be 8 ohm. They will be wired in parallel.
Many thanks Guitologist!
I've since worked out the basic particulars on ohm. I'm having a go at building my own cab, & I have come to realise My Marshall is indeed wired parallel, thus halving the impedance load.
Many Regards.
Marshall made two versions of this circuit....... you want the JMP50C power section schematic here: www.next.gr/uploads/51/cd0192-iss10.gif (this amp in the video is the EL34 version based on the 2k2 caps R31 through R34)
Pots connected to the board. Such a bad idea!
you dont have to bias these beasties they are replace and play
Peter Green fan, eh?
Sure. I like Peter Green. Not sure I play like him though. A few guys have said I sound like Terry Kath, but I don't know about that either.
I recognized the song you played and was surprised/happy that someone else would be playing it, thanks for that. Your playing is absolutely on a level with dudes of that ilk, it's all good. I bet it's reason for a lot of your subs. The music is in your soul(or whatever), it takes a certain kind of player who can have impromptu jam sessions, ALONE. No script, no music, just a guit-fiddle and some amplification, sometimes acoustic. Tons of us dig your playing man, please keep on keeping on. Many thanks for time spent entertaining us and much respect.
Wow! I'm blown away and humbled by your comment. It really means a lot to me. Thank you!
i owned a 2x12 model. not a good sound in that thing anywhere. that's why you don't see many.
I swear Marshall produces shit documentation deliberately. It's impossible to locate the exact print for the amp you're currently working on. I have never had the exact print for the amp I'm working on, it's always close but no cigar. Even trying to follow how their print numbering system is a pain in the ass. A real time waster until you make a marked up set of prints.
900 sucked,800 ruled
I have a question, could using the wrong rectifier tube cause a power tube to burn out? Example, I have a tube amp that called for a 5az4 rectifier tube and actually what I put in there was a 6x5, could this be responsible for to cause one of the power tubes to burn out? Thanks for any help on this. I know that there are suitable replacements on these type tubes but a 6x5 is never mentioned in the possible substitutes.
I have a question, could using the wrong rectifier tube cause a power tube to burn out? Example, I have a tube amp that called for a 5az4 rectifier tube and actually what I put in there was a 6x5, could this be responsible for to cause one of the power tubes to burn out? Thanks for any help on this. I know that there are suitable replacements on these type tubes but a 6x5 is never mentioned in the possible substitutes.
I have a question, could using the wrong rectifier tube cause a power tube to burn out? Example, I have a tube amp that called for a 5az4 rectifier tube and actually what I put in there was a 6x5, could this be responsible for to cause one of the power tubes to burn out? Thanks for any help on this. I know that there are suitable replacements on these type tubes but a 6x5 is never mentioned in the possible substitutes.
I have not compared those tube data sheets, but your rectifier creates your B+ voltages, so yes, a bad or wrong rectifier might cause another tube to burn up, or any number of other components associated with the power supply - screen resistors, power caps, power resistors, cathode bias resistors, plate resistors, Output Transformers, etc.