1967 JMP 50 circult

stblack

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Yes, the 'Lead' and the 'Organ' models shared the same circuit as far as I've seen. Marshall's marketing scheme was to associate different speaker cabinets with each model in order to differentiate them further. Their catalogs refer to these as 'setups'.
You are right that the reed and organ are on the same circuit. I can feel the days when the organ was running rampant!
 

neikeel

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Summary: late 67 Bass/lead or organ originally
Replaced switches and lamp
Replaced filter caps and boas caps
Added screen resistors and grid resistors
Output coupling caps replaced 0.1uF to 0.022uF
Added 0.68uF cap over V2a cathode
Replaced output tube sockets

So partly modded to lead spec but preserving shared cathode v1 and no cap on the volume pot
 

stblack

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Summary: late 67 Bass/lead or organ originally
Replaced switches and lamp
Replaced filter caps and boas caps
Added screen resistors and grid resistors
Output coupling caps replaced 0.1uF to 0.022uF
Added 0.68uF cap over V2a cathode
Replaced output tube sockets

So partly modded to lead spec but preserving shared cathode v1 and no cap on the volume pot
Thankyou,Detailed description, looks like a very courteous repair. But it is a "mod".
 

neikeel

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It all looks to have been done very professionally and tidily, no issues with quality of work or parts but yes definitely modded.
 

shakti

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My JTM45 is an organ model. Only difference I can see from a lead amp is that it has only one speaker jack. Not sure if all organ model JTM45s were like that though.
 

stblack

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It all looks to have been done very professionally and tidily, no issues with quality of work or parts but yes definitely modded.
Yes, I thought so too. The selection and placement of parts that are close to the original signal line are very beautiful. But "MOD"
 

stblack

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My JTM45 is an organ model. Only difference I can see from a lead amp is that it has only one speaker jack. Not sure if all organ model JTM45s were like that though.
Thank you very much. It's the first time I've heard of it.
 
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Pretty good info given. Disregard anything my avatar wrote here.
 
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stblack

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I wish there where more setups like that being used nowadays lol.

On the earlier 50 watts that I mentioned earlier it …Is probably a good move to put 3 or 5 watt 1k screen grids in it rights? Also the 2 smaller grid blocking resistors (I can not remember what they are call)? Where do those little resistors go ? I hear they cut back oscillation .

I have a good stash of old Mullard el34s. However maybe screen grids are still needed with old el34s?
I am not highly knowledgeable. I am just doing what people have recommended. Could someone please tell me what I need to know?
 
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I am not highly knowledgeable. I am just doing what people have recommended. Could someone please tell me what I need to know?
Word ,didn’t mean to change course of your thread. New To forum behavior Lol. No problem disregard my questions about similar but different amp in main thread here. Its your thread and you have the right people here helping you . I hope you find what you looking for . Cool amplifier a hundred or so serial number way from mine is also only reason I commented. :bump:
 
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stblack

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I am very pleased to see that some of you are interested in this thread. The purpose of this thread was to find out if the circuit of this unit I saw on Reverb is rare, a modification, or if it exists in its original form. I also wanted to know if the name change from JTM to JMP was not just a name change, but the beginning of a new product line. I had a JTM50 but gave it away. I now own a late 68 or later head.
 

TAZIN

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I also wanted to know if the name change from JTM to JMP was not just a name change, but the beginning of a new product line.
The name change from JTM (Jim & Terry Marshall) to JMP (Jim Marshall products) had nothing to do with a new product line. The name change is outlined in the History of Marshall book.
 

stblack

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The name change from JTM (Jim & Terry Marshall) to JMP (Jim Marshall products) had nothing to do with a new product line. The name change is outlined in the History of Marshall book.
thankyou I will read it.
 

sct13

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I have a 68/ early 69 JMP, its slightly different in cap placement. Sounds amazing. It did have a transformer replacement many years ago. But its the correct one 784-139
 

stblack

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I have a 68/ early 69 JMP, its slightly different in cap placement. Sounds amazing. It did have a transformer replacement many years ago. But its the correct one 784-139
thankyou.your nice marshalls! what any diffrent stage?
 

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