Incoming JCM 900 Mkiii
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- handsoffmatt
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Re: Incoming JCM 900 Mkiii
edited..
Last edited by handsoffmatt on Tue Mar 24, 2020 9:41 am, edited 1 time in total.
"Volume is tone" - EVH
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- griff
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Re: Incoming JCM 900 Mkiii
Any EL34 recommendations for this amp? I'm not too clued up on the ins and outs of 34's..
I will be using this with an attenuator so there will definitely be a cooking power section in this amp when I use it.
I will be using this with an attenuator so there will definitely be a cooking power section in this amp when I use it.
- handsoffmatt
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Re: Incoming JCM 900 Mkiii
Just rechecking schems....and although I'm not what you would call an electronics expert.... it still looks to me that the following is true, unless I'm sorely misunderstanding something.handsoffmatt wrote:Optical wrote:?? that's not right at all...handsoffmatt wrote:
JCM900 mkIII 2100(100W) / 2500 (50W) models. These are essentially identical circuit to 2203/2204 but with a diode clipper added for more gain and footswtichable dual master volumes. Later on, the 2100 / 2500 became known as the SL-X, which removed the diode clipper and added an extra preamp tube gain stage.
It has less gain stages than a 2203/4, and the SLX has two more gain stages than the 2500 and shares almost nothing in common circuit-wise...
The 2100/2500 have the same number of valve gain stages as a 2203/2204 (3 stage + cathode follower), plus an added diode clipper. Take the diode clipper out and the preamp design is pretty darn similar to a 2203/2204, albeit with some value changes here and there.
The 2100/2500 SL-X versions ditch the diode clippers, and add an additional tube gain stage - so in the preamp section is very much like a hot-rodded 2203.
There are however marked differences in the poweramp/NFB circuits in the JCM900's as opposed to the JCM800's.
Schematic sources here:
https://www.thetubestore.com/marshall-schematics
"Volume is tone" - EVH
Electrics: ESP/Fender/Gibson/.strandberg*/Godin/Washburn/Music Man/Knaggs/Squier/Vintage
Acoustic: Cole Clark/Godin/Takamine/Taylor
Amps: BOSS Katana Head / Friedman Smallbox
Electrics: ESP/Fender/Gibson/.strandberg*/Godin/Washburn/Music Man/Knaggs/Squier/Vintage
Acoustic: Cole Clark/Godin/Takamine/Taylor
Amps: BOSS Katana Head / Friedman Smallbox
Re: Incoming JCM 900 Mkiii
Ah yes I see your point. The second stage has local out of phase mixing and some NFB, so really a frequency shaping stage rather than a gain stage. however there are two gain controls which i hadnt noticed, so the gain reduction can be dialed out, interesting.
- jeremyb
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Re: Incoming JCM 900 Mkiii
Always had good experience with JJs in the past, dunno what else is available these days!griff7628 wrote:Any EL34 recommendations for this amp? I'm not too clued up on the ins and outs of 34's..
I will be using this with an attenuator so there will definitely be a cooking power section in this amp when I use it.
Slowy wrote: That's the problem; everything rewarding is just such hard work. Regret takes much less effort.
- godgrinder
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Re: Incoming JCM 900 Mkiii
I had more brand new JJs die on me in a few months than Shuguangs for some reason.jeremyb wrote:[
Always had good experience with JJs in the past, dunno what else is available these days!
Amps:
Soldano SLO100 x2 | Wizard MC1 & MC2 | Diezel Herbert
Fryette Pittbull CL | Marshall 2203KK | Krank Rev 50 | Mesa Mark 2A
Rack stuff:
VHT/Fryette GP3, GP/DI & 2/90/2 | Peters FSM/Chimera
Verellen Meatsmoke | Synergy SYN1 | Mesa Studio
Soldano SLO100 x2 | Wizard MC1 & MC2 | Diezel Herbert
Fryette Pittbull CL | Marshall 2203KK | Krank Rev 50 | Mesa Mark 2A
Rack stuff:
VHT/Fryette GP3, GP/DI & 2/90/2 | Peters FSM/Chimera
Verellen Meatsmoke | Synergy SYN1 | Mesa Studio
- jeremyb
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Re: Incoming JCM 900 Mkiii
They probably implode when you tune to drop Z!godgrinder wrote:I had more brand new JJs die on me in a few months than Shuguangs for some reason.jeremyb wrote:[
Always had good experience with JJs in the past, dunno what else is available these days!
Slowy wrote: That's the problem; everything rewarding is just such hard work. Regret takes much less effort.
- godgrinder
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Re: Incoming JCM 900 Mkiii
More like they dropped the balls in the last 2-3 years. I found that if they don't die during the first year they'll be fine for a while, but some of them can't.jeremyb wrote: They probably implode when you tune to drop Z!
If I buy an used amp with JJs I wouldn't swap them out but I no longer buy brand new ones.
Amps:
Soldano SLO100 x2 | Wizard MC1 & MC2 | Diezel Herbert
Fryette Pittbull CL | Marshall 2203KK | Krank Rev 50 | Mesa Mark 2A
Rack stuff:
VHT/Fryette GP3, GP/DI & 2/90/2 | Peters FSM/Chimera
Verellen Meatsmoke | Synergy SYN1 | Mesa Studio
Soldano SLO100 x2 | Wizard MC1 & MC2 | Diezel Herbert
Fryette Pittbull CL | Marshall 2203KK | Krank Rev 50 | Mesa Mark 2A
Rack stuff:
VHT/Fryette GP3, GP/DI & 2/90/2 | Peters FSM/Chimera
Verellen Meatsmoke | Synergy SYN1 | Mesa Studio
- willow13
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Re: Incoming JCM 900 Mkiii
I think a lot of the boutique amp makers (friedman etc) stopped using JJ's a while ago due to unreliability
If Less is More Then Just Think How Much More More would be
- godgrinder
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Re: Incoming JCM 900 Mkiii
And they are not even cheap which makes it even worse. I don't mind Shuguang's dying since I can get their power tubes for $10 a pop (but funnily enough I hardly ever had Shuguang's die on me other than from old age).
Amps:
Soldano SLO100 x2 | Wizard MC1 & MC2 | Diezel Herbert
Fryette Pittbull CL | Marshall 2203KK | Krank Rev 50 | Mesa Mark 2A
Rack stuff:
VHT/Fryette GP3, GP/DI & 2/90/2 | Peters FSM/Chimera
Verellen Meatsmoke | Synergy SYN1 | Mesa Studio
Soldano SLO100 x2 | Wizard MC1 & MC2 | Diezel Herbert
Fryette Pittbull CL | Marshall 2203KK | Krank Rev 50 | Mesa Mark 2A
Rack stuff:
VHT/Fryette GP3, GP/DI & 2/90/2 | Peters FSM/Chimera
Verellen Meatsmoke | Synergy SYN1 | Mesa Studio
- higainer
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Re: Incoming JCM 900 Mkiii
Thiswillow13 wrote:I think a lot of the boutique amp makers (friedman etc) stopped using JJ's a while ago due to unreliability
Svetlana’s have done right by me.
- godgrinder
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Re: Incoming JCM 900 Mkiii
If you want more 6L6 flavour then yes.griff7628 wrote:Are KT77's worth considering for this amp?
Amps:
Soldano SLO100 x2 | Wizard MC1 & MC2 | Diezel Herbert
Fryette Pittbull CL | Marshall 2203KK | Krank Rev 50 | Mesa Mark 2A
Rack stuff:
VHT/Fryette GP3, GP/DI & 2/90/2 | Peters FSM/Chimera
Verellen Meatsmoke | Synergy SYN1 | Mesa Studio
Soldano SLO100 x2 | Wizard MC1 & MC2 | Diezel Herbert
Fryette Pittbull CL | Marshall 2203KK | Krank Rev 50 | Mesa Mark 2A
Rack stuff:
VHT/Fryette GP3, GP/DI & 2/90/2 | Peters FSM/Chimera
Verellen Meatsmoke | Synergy SYN1 | Mesa Studio
- willow13
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Re: Incoming JCM 900 Mkiii
I think you might need to swap out some resistors to be able to run them??griff7628 wrote:Are KT77's worth considering for this amp?
If Less is More Then Just Think How Much More More would be