Tube layout

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Hollywood

Hollywood

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I have a modded marshall that I just spent a half a day with to pick the best bias for the power tubes. That being all set it is now time to play the pre-amp tube game. I have 4 pre-amp tubes/sockets in this amp . The amp is a 78 Marshall jmp.
the 1st 3 pre-tubes are what I am trying to make sure of their exact purpose. the last pre-tube, 4th or added pre-tube is the new one installed by the amp builder/modder. so that one is the extra kick in gain stage. So who has or knows exactly the layout for a 78 2203 100 watt marshall jmp?
1st closest to the power tubes, 1st gain stage, 2nd or next from there the 2nd gain stage?, then the Phase inverter is the 3rd or next before the new 4th pre tube ? This is my best guess. I have also been hearing about trying the 12 at7's and 12au7's in this amp? :confused: Let me know. :yes: I have alot of pre tubes to choose from so I just wanna be correct before I start this pull one at the time experiment. :rock:
 
the old Marshall had a lot of room between the preamp tubes, sometimes the modders will sneak the 4th tube between what used to be just the 3. look for the 4th being bolted instead of riveted.

the 3rd of the originals should be the PI, and should be closest to the power tubes. i'm allways paranoid to change the PI after biasing, scared it will change the bias, but don't know for sure?
 
I definately got the new pre amp tube and socket pegged. :yes: Big cosmetic give away. I am downloading the 2203 manual from the marshall website right now it should have this info on there. I did some reading from an article doug Rappaport wrote on biasing and pre tubes and according to that article none of the pre tubes will affect the bias.
But the pi pre tube has something to do with a split of some kind where as signal for the two outer tubes and signal from the pi going to the inner two tubes are seperated btween the pairs coming from the PI pretube. If this is true then maybe a guy should not remove a pair of tubes on a 2203 just to try and make the amp lower volume. It really some how would affect the tone. :confused:
 
:lol: :LOL: I got me a new marshall 2203 manual printed out but ....NO TUBE LAYOUT. :doh:
 

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My modded jmp has the extra pre tube added beside the v1 farthest to the left. So v1 will be 1st gain stage and v-2 will be 2nd gain stage and v-3 is the PI tube yes? Thanks for the pic I really appreciate it. ;) hey what type of pre tubes are you running?
 
The original V1-V3 should still be as per original design with the new gain stage inserted between the original V2 and V3. The original V3 should still be the PI tube. You can pull the chassis and look at it and probably tell.

I have SOVTEK 12ax7 LPS's in all the preamp positions and SED Winged C EL34's for power tubes.


Steve
 
Right now this amp has all chinese pre tubes in it. The extra pre-tube may be wired into the chain between the v-2 and v-3 but on top it sits to the far left on the end. Not enough room to have squeezed it between the v-2 or v-3 pre's. :lol: :LOL: :doh:
the sovtek lps pre's are the one or two tubes I don't have right now. I got Electro harmonix, JJ's, chinese 8th and 9th gens. Sovtek wa's wb's wc's , nos jj's, nos westinghouse, nos GE, high gain jj's bunch of ruby's ruby high gains, GT 12 ax7 moderns, GT ecc83 NOS, Ge's from before I was born.. a few NOS mullards, new re-issue mullards . no tung sols though or the sovtek lps pre's.... :doh:
 
there's no telling which tube does what at this point. i'm sure the PI is the same, and V2 is probably still the cathode follower, but which tube is the first gain stage is any body's guess. do you know who modded it? maybe he can tell you what the tube layout is...
 
Lps or long plate spiral pre tubes are not supposed to go into the cathode follower slots in marshalls right? That would be #2. v-2 yes. typically speaking this is something I think I remember...yes? I know the bogner rev. blue uber is this way... no LPS in the cathode follower slot. :)
 
Hollywood":5t7nm2yn said:
Lps or long plate spiral pre tubes are not supposed to go into the cathode follower slots in marshalls right? That would be #2. v-2 yes. typically speaking this is something I think I remember...yes? I know the bogner rev. blue uber is this way... no LPS in the cathode follower slot. :)
Click to expand...
True. Although the LPS is known to preform well in the PI spot, sp stick it in there for starters. Then swap around your other supply of tubes in rest of the slots.
I wonder which is the preamp input tube...the added spot, or the now second tube inline?
 
If that's the Golub 78 JMP, then the added tube is V1 (first stage), next is V2 (2nd and 3rd stage), then V3 (4th stage and CF) then V4 (PI).

Hope that helps Hollywood :rock:
 
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