convert a JCM-2000 to JMP or JCM-800

[ALBATROS1234]

A friend was gifted a broken JCM-2000 TSL100 which has issues. He started playing in  classic hard rock/80s metal cover band. They want to eventually play shows and they want to be loud. My buddy has a 30watt Orange which isnt keeping up with the other guitarists rig. So he is given a 2000 and wants me to fix it. Right now it has run away power tubes red plating plus it has a strange volume issue where when you crank it up it sounds ok but as if it is a 1watt amp which is barely loud enough for the bedroom. I haven't pulled the chassis but I started research because I am not familiar with this amp nor modern amp designs and I only have experience working on, building and modding p2p style amps. I have found videos and forum stuff which says these amps have issues with the board(s) going conductive which has sent many techs chasing their tails and ending up having to buy a new board.

Enter my Idea. Since its likely a board issue and not the iron etc. I started to think why not convert it to a 70s JMP100 or early 80s JCM-800.Does this sound crazy? Obviously I will have to do something with the control panel. But other than that It doesnt seem like too hard of a job. Just basiclly rip out the old boards buy a Marshal turret board for a classic model to be determined and follow a layout/schematic to build something which will be more robust electronically and likely sound better. Are there any problems with doing this that are known but I havent considered or should I go for it. My friend just wants a classic Marshall 100watt head and is fine with just a one channel amp which sounds loud and good. For that matter I have considered doing the exact same thing to an old Carvin 100xb which I have that only one channel works and I dont care for the tone. Please advise. Does this seem like a bad idea to convert partially working amp using the Iron and odds and ends with a new handwired board.Thank you

[Latole]

".   Right now it has run away power tubes red plating plus it has a strange volume issue where when you crank it up it sounds ok but as if it is a 1watt amp which is barely loud enough for the bedroom.  "

- Albatros1234

________________________

Tubes red plating !!! 

Don't use amp until bias is checked and adjusted or / and with new tubes 

Be sure amp have the right fuse if you don't want to destroy the Power Transformer

[Joel in Texas]

First, even though I don't know what's up with the amp based on available info so far, I agree with Latole: I would stop using the amp until you have more fully diagnosed the problems and/or taken appropriate steps to fix some of the issues.  Based on the symptoms you have described, you could possibly end up with a blown power transformer or other damage, if you or others keep running it as-is.

Second, yes: it is possible to tear down a PC-board based amp, and rebuild it point-to-point as another model of amplifier.

I've never owned or worked on a TSL100 myself.  So I can't comment specifically on possible success in starting with that particular model and ending up with something more like a JCM800 or JTM100.  But my guesses are (1) you could probably find someone who has done it, using your ol' google machine and (2) it would probably work.

More generally, you can definitely find where people have done similar things - tearing down a PC-board amp, and rebuilding point-to-point.  Doug Hoffman (sponsor of this website / board) has similar projects described in detail, and sells turret boards etc. needed to get them done.  Here is an example of one such project:

https://el34world.com/Hoffman/Blues_Junior_Build.htm

[glass54]

Hi Albertross1234,
Personally I'd gut it!!
Mind you, the cabinet and chassis is quite large. I would do build based on a Marshall JCM800 2203 for simplicity, BUT use the Reissue schematic (https://el34world.com/charts/Schematics/files/Marshall/Marshall_2203_reissue.pdf) minus the FX card ie Link X3 and X4. The main reason I say this is the Iron in your amp JCM2000 is closer to the "reissue" hardware. The original 2203 was a fine gutsy amp.
You could use the Hoffman Plexi 50 Turret board with mods and cater for the 4 output Tubes. If you feel confident enough, I'd go for it, as you will get help from the forum. https://el34world.com/Hoffman/files/Hoffman_Plexi50.pdf
The original Marshall JCM-2000 TSL100's were real dogs here in Aussie in the early 2000's and I would often blame our supply of poor quality output tubes (remembering at that time that Aussie got the "leftover dregs" or pay huge premium prices to import  good stuff). But as time went on, all the problems you hear about with these, came true. Keep an eye on correct heater volts when Mains Tx is correctly loaded and occasionally I have replaced output transformers with the JCM2000s. Mains transformers were reliable, PCBs
Just my 2 cents worth.
Kind Regards
Mirek

[AmberB]

If the "Marshall PC board going conductive" problem is what's going on, you're probably going to have to replace the board anyway.  In that case, you can use a turret or grommet board and either just rebuild the circuits as they are now, or modify the design to an older type.  If you follow the schematic off your choice, I don't see any reason why it wouldn't work.

[Latole]

I think you should rather repair the JCM2000 TSL100 rather than rebuild an amp.
Start by repairing the Red Plating.
Then you will see for the other problems if there are any.

About the card that would cause problems, I don't know. All I know is you shouldn't believe everything you read on Google. They too often lack details or the "technicians" who would have said that are often amateur DIY enthusiasts, not technicians

[Latole]

".... started research because I am not familiar with this amp nor modern amp designs and I only have experience working on, building and modding p2p style amps."

- Albatros1234

I repair and build a lot of amps. Like you, I happened to meet an amp with which I was not used, which seemed to me to be unrepairable because it was too different from my P to P that I know well.

I put aside the amp for a few days, time to take a step back, and finally tamed the beast and fixed it.

In this profession, patience is essential.

You'll see, it is easier to fix it than to built a new one which will undoubtedly have problems to repair

[pdf64]

Bad pcbs, whose substrate material fails over time resulting in redplating, is a known issue with early dsl / tsl. Marshall made proper replacement boards available for a reasonable cost. 
Here’s a thread on the topic https://music-electronics-forum.com/forum/amplification/guitar-amps/maintenance-troubleshooting-repair/41629-marshall-dsl100-replacement-boards/page2

[Latole]

Red plating is a bias circuit issue.

It is surely possible to rebuild this small power supply on a separate bead board.

[ALBATROS1234]

First off i am not using it, my friend dropped it off he had not turned it on because he was told it was broken. I turned it on and stroked a couple chords and got no volume so i looked at the back and saw red plating so i turned it off. Today I poked around on the internet and saw that run away bias is a problem on these amps, the pcb goes conductive. There are pins sticking out back to test bias so i clipped on my dmm and when i flipped on the standby instead of going to 90mv it jumped to 160 and slowly kept climbing causeing red plating within a few minutes on all tubes. so the combination of the low volume and runaway bias is enough to make me rebuild it . I have build several amps at this point both from scratch as well as modding r2r amps and amps from 50s projectors etc. so i think it shouldnt be too bad to convert it to turret board . I think maybe as suggested i will go for the jcm800. Honestly I don't understand why companies build such over engineered behemoths . Give me a basic tube amp that I can crank into creamy tubey goodness and I am happy. The main thing I have noticed from the amps I have built and vintage point to point/ turret board types vs modern pcb types is you can hear the difference in different guitars with a basic tube amp, to me if i plug into a fender blues deluxe or whatever with a les paul then plug in a tele they dont sound too much different but its really apparent with a simple amp design. thank guys. I will probably rebuild this one then later convert my carvin into a plexi style.

[DummyLoad]

Honestly I don't understand why companies build such over engineered behemoths

marketing BS.

i want ultra clean with reverb and tremelo, and selectable tone controls, and overdrive with reverb, and effects loop, oh yeah, and i want tweed tone, and plexi tone, and ODS tone, and 100W...all in the same box.

 

--pete