Santiago Alvarez (electronics engineer, JVM, YJM, AFD...)

I looked the amp with thermal camera and FS5 got my attention.. it was much hotter compared to other fuses, Sorry for lousy quality.

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Also R118 and R75 were hotter than other resistors:
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R75

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Does these look normal to you?
 

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Just disassembled the whole amp, measured every single cable and checked boards for bad solders... there were no issues in the connectors, cables or solders. Maybe i'll just get new JVM410 and this will remain as mystery... world needs unexplained phenomenons :D
 
Jonttu said:
Just disassembled the whole amp, measured every single cable and checked boards for bad solders... there were no issues in the connectors, cables or solders. Maybe i'll just get new JVM410 and this will remain as mystery... world needs unexplained phenomenons :D
Click to expand...
That’s herds of work man!!!
 
Jonttu said:
Just disassembled the whole amp, measured every single cable and checked boards for bad solders... there were no issues in the connectors, cables or solders. Maybe i'll just get new JVM410 and this will remain as mystery... world needs unexplained phenomenons :D
Click to expand...
yes, it is very weird indeed but if the connection is intermittent it is very possible that when you verify the wires they'll test ok.
 
santiall said:
yes, it is very weird indeed but if the connection is intermittent it is very possible that when you verify the wires they'll test ok.
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That's true.
I try to get new front pcbs... we will see what happens after that :D Im sure that once i've replaced every component it works eventually! :)
 
Jonttu said:
That's true.
I try to get new front pcbs... we will see what happens after that :D Im sure that once i've replaced every component it works eventually! :)
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yeah, that's for sure, brute force repair techniques hahahah, I hope you aren't remortgaging your house to afford the bills...
2nd hand JVMs aren't that expensive :D
 
santiall said:
yeah, that's for sure, brute force repair techniques hahahah, I hope you aren't remortgaging your house to afford the bills...
2nd hand JVMs aren't that expensive :D
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Hahaha! Indeed! :rofl
It seems that Marshall doesn't sell PCB's anymore... well, i will replace every IC, every relay, all transistors on the front pcb's and hardwire every single connection between without connectors.. Am i stupid? Yes i am. But this is too deep in personal level allready!

I promise that i won't never bother you again with this issue!
Huge thanks for your replies and endless patience with me! (y)
 
Jonttu said:
Hahaha! Indeed! :rofl
It seems that Marshall doesn't sell PCB's anymore... well, i will replace every IC, every relay, all transistors on the front pcb's and hardwire every single connection between without connectors.. Am i stupid? Yes i am. But this is too deep in personal level allready!

I promise that i won't never bother you again with this issue!
Huge thanks for your replies and endless patience with me! (y)
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You can ask any time of course, I'm actually curious about what's actually going on. Also I feel bad with you changing everything and still no progress...
 
santiall said:
You can ask any time of course, I'm actually curious about what's actually going on. Also I feel bad with you changing everything and still no progress...
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Me too! Very curious! I'll let you know what happens once i get all the components changed :)
 
Hi Santiall,

Was wondering if i could get your professional technical opinion / personal opinion on some of the following, things that some people do to reduce the gain \ volume etc on a JVM 210C. Please excuse me if i say anything generic or stupid and any feedback welcome.


- Placing an ECC823 in V1 to just affect OD orange and red

- Placing a 5751, in V1, V2

- Placing a 5751 in the PI slot

- Removing 2 output tubes

I love the amp and cranking it in a band setting, just curious on the above as i have a second unit that just sits at home.

Regards

Liam
 
liamoftheshire said:
Hi Santiall,

Was wondering if i could get your professional technical opinion / personal opinion on some of the following, things that some people do to reduce the gain \ volume etc on a JVM 210C. Please excuse me if i say anything generic or stupid and any feedback welcome.


- Placing an ECC823 in V1 to just affect OD orange and red

- Placing a 5751, in V1, V2

- Placing a 5751 in the PI slot

- Removing 2 output tubes

I love the amp and cranking it in a band setting, just curious on the above as i have a second unit that just sits at home.

Regards

Liam
Click to expand...
Hi, you can try any of those, nothing is going to be damanged for testing those different tubes or removing two output tubes.
For V1 you could try an ECC832 as well, in the JVM the input valve is the second triode in the tube. It'll give you a different amount of gain for all the channels instead of only the high gain ones.
Removing two output tube will technically lower the outpot power to 50W but not sure how worth it is as the difference in volume is subtle.
 
Watched the Headfirst Amp Chat with you, Santiago, and Jason, which by the way was very entertaining and again lots of helpful hints and things. :D

Question to Santiago:
When talking about the Jubilee reissues, I remember you mentioned, that in the "usual" schematics from the 1987/88 originals there was one supposedly 100n cap, which wasn't there (or was different?) on the original amp in the Marshall museum.
Do you remember which one exactly, when looking at the schematic?
https://www.drtube.com/schematics/marshall/2555amp.gif
I'd say , the ones which would have a rather noticeable impact on the tone would be those in the tone stack...
 
James Freeman said:
Maybe V8b has some grid to cathode leakage causing R75 and R118 to see a lot of current.
Pull V8 out, check again.
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Could be? I will replace the tube once i put the amp back together.

I removed every IC, transistor and relay from the frontboards and now im waiting for new components to arrive.



IMG_0366.jpeg
 
santiall said:
Hi, you can try any of those, nothing is going to be damanged for testing those different tubes or removing two output tubes.
For V1 you could try an ECC832 as well, in the JVM the input valve is the second triode in the tube. It'll give you a different amount of gain for all the channels instead of only the high gain ones.
Removing two output tube will technically lower the outpot power to 50W but not sure how worth it is as the difference in volume is subtle.
Click to expand...
Thanks Santiall, have ordered a ECC832 also to try. Think i will leave the output tubes alone and also try to get my head around the PI circuit and how changing tubes in that may or may not chnage things like the presence \ resonance etc with the v30s i have. (been a while since done any real electronics eng) Will most likely leave it alone though.

appreciate the help.

Liam
 
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headcrash said:
Watched the Headfirst Amp Chat with you, Santiago, and Jason, which by the way was very entertaining and again lots of helpful hints and things. :D

Question to Santiago:
When talking about the Jubilee reissues, I remember you mentioned, that in the "usual" schematics from the 1987/88 originals there was one supposedly 100n cap, which wasn't there (or was different?) on the original amp in the Marshall museum.
Do you remember which one exactly, when looking at the schematic?
https://www.drtube.com/schematics/marshall/2555amp.gif
I'd say , the ones which would have a rather noticeable impact on the tone would be those in the tone stack...
Click to expand...
I'd need to check but I think that schematics looks ok. I remember that back in the day, the most popular schematics had a value written by hand and it was wrong. Our service schematics and the original amp were different to that schematic online
 
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