'82 Marshall JCM 800 4010 combo blowing fuses

  • Thread starter Thread starter BluesManRocker
  • Start date Start date
BluesManRocker said:
However this one has a trim pot for biasing, so I guess this one is better, but includes too much and is twice as expensive. So I messaged the seller about if they could provide one without the pots attached, and how much for it. But then I just realized, it's out of stock, so I'll be lucky if i get a response back. I would not mind paying $150 for a nicely appointed main board, and just swap the entire board out. I much prefer better caps and point to point wiring.

I don't want to pay 200 for it, without pots and jacks. although it would save me soldering time. I guess I could sell my brand new pots I just purchased. But I'd much prefer just not buying what I already have. I am brand new to turret, point to point, main boards, but have long desired it. Let me know what you think.

View attachment 44445
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Where are you located?
You don't need to do any of this. You don't need any circuit boards.

Don't rip apart a good amplifier.
Get to a professional and get the amp fixed right.

If I was there I would have that pup up and going in 2 hours. All this other stuff is useless.
 
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Ampmad, blues is in Michigan. No car and low finances. I concur about the no swap to P 2P. Not needed just for a few tweaks any pro should easily be able to do. The few parts it should need are negligible, and labor should not be hateful.
 
chilipeppermaniac said:
Ampmad, blues is in Michigan. No car and low finances. I concur about the no swap to P 2P. Not needed just for a few tweaks any pro should easily be able to do. The few parts it should need are negligible, and labor should not be hateful.
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The stock amp works just fine.
The stock amp is considered one of the best ever made.
Why play around with it?
Just get it put back to stock and play it.

Modifying this amp is a bad idea. It's going to create more problem then it solves.
No, you do not need to change any capacitors except 2.
Just 2X 10uF caps, that's all.

Get a professional.

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I will call Elderly music, as they are a half mile from me, but I already called them when I moved here and the amp first broke down, and they said they don't do amp repairs anymore, but we have a local repair shop that we recommend. I can't say if that guy is still in business or not, but I can't take my amp to another city bro, and to have them come to me would mean an astronomical fee. It's very likely I will not find a local amp tech close enough. That is just reality brother. I need to make my calls again, yes, but I'm warning you, to not be surprised if there are none around me.

And I trust your judgment, but not as far as just those two caps or resistors go, no, I want my amp to sound great and get rid of that base resonance, that bugged me to no end when he put that on my amp. It seems kinda gone over the years, but can't say for sure. However at the time, I hated it.

So far, unless I get lucky and find a local and trust worthy amp tech, replacing the main board seems like the best option, and I can do it myself. In fact, I'd go for the JMP master volume, so I'd have exactly the amp I'd want with better input selection, and better tone architecture throughout. I welcome more comments.
 
BluesManRocker said:
I will call Elderly music, as they are a half mile from me, but I already called them when I moved here and the amp first broke down, and they said they don't do amp repairs anymore, but we have a local repair shop that we recommend. I can't say if that guy is still in business or not, but I can't take my amp to another city bro, and to have them come to me would mean an astronomical fee. It's very likely I will not find a local amp tech close enough. That is just reality brother. I need to make my calls again, yes, but I'm warning you, to not be surprised if there are none around me.

And I trust your judgment, but not as far as just those two caps or resistors go, no, I want my amp to sound great and get rid of that base resonance, that bugged me to no end when he put that on my amp. It seems kinda gone over the years, but can't say for sure. However at the time, I hated it.

So far, unless I get lucky and find a local and trust worthy amp tech, replacing the main board seems like the best option, and I can do it myself. In fact, I'd go for the JMP master volume, so I'd have exactly the amp I'd want with better input selection, and better tone architecture throughout. I welcome more comments.
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In my own opinion I wouldn't do any modifications.
But get it working right before anything else.

The repair guy will probably pick it up and deliver it.
If it's only 1/2 mile away it won't be difficult.
The Elderly is listed as a certified tube amp service center, and they should have no problem.
Meaning the tech is qualified and uses test equipment.
 
BluesManRocker said:
I will call Elderly music, as they are a half mile from me, but I already called them when I moved here and the amp first broke down, and they said they don't do amp repairs anymore, but we have a local repair shop that we recommend. I can't say if that guy is still in business or not, but I can't take my amp to another city bro, and to have them come to me would mean an astronomical fee. It's very likely I will not find a local amp tech close enough. That is just reality brother. I need to make my calls again, yes, but I'm warning you, to not be surprised if there are none around me.

And I trust your judgment, but not as far as just those two caps or resistors go, no, I want my amp to sound great and get rid of that base resonance, that bugged me to no end when he put that on my amp. It seems kinda gone over the years, but can't say for sure. However at the time, I hated it.

So far, unless I get lucky and find a local and trust worthy amp tech, replacing the main board seems like the best option, and I can do it myself. In fact, I'd go for the JMP master volume, so I'd have exactly the amp I'd want with better input selection, and better tone architecture throughout. I welcome more comments.
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I guess my tech tip is: Never modify a broken amplifier.
Don't try to fix an amplifier, and modify it at the same time.

Fix it 100% first, play it and make sure all the bugs are fixed solid.
When it works 100% no problems:
Then (and only then) if you really want to modify any part of it the this is the time.
But you don't need any circuit board.
 
Amp Mad Scientist said:
In my own opinion I wouldn't do any modifications.
But get it working right before anything else.
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^^^^^^ This, definitely ^^^^^^^

@BluesManRocker
Start with the small stuff first. Definitely replace the pair of electrolytic caps of the bias circuit with the proper values. Note the orientation of the caps (polarity). Replace the single resistor that AMS is suggesting to obtain a proper bias range. With what value, I'm not sure. Or, replace the first bias range resistor after the bias trimpot. The one on your amp is a 47K, and it should be a 56K according to the schematics of your amp when using EL34's. Get that amp biased properly. Hopefully there are no other underlying conditions affecting your amp's proper operation.
 
They are not open until 11. So I have to wait for an hour and a half.

I'm looking at the job at hand, and I don't see why it can't be done from the top

If you leave the legs long from the former dodads, can't we just weld the new stuff to em? Fill in proper turminolegy accordingly.

What is wrong with doing a great topside job? Makes all our lives much easier, hmmm? Why do I feel like I'm in a loosing battle. Cause I have a great amp that is not quite right,, it's fallen and can't get up. I never had such a great set of tubes waiting for my amp to work. And a new speaker too. And it's been 5-6 years since I've played it, so it means the world to me, to have it working properly.

If only money and logistics was not an issue. Here's hoping Elderly has something close by, or it seems that I am on my own.
 
BluesManRocker said:
They are not open until 11. So I have to wait for an hour and a half.

I'm looking at the job at hand, and I don't see why it can't be done from the top

If you leave the legs long from the former dodads, can't we just weld the new stuff to em? Fill in proper turminolegy accordingly.

What is wrong with doing a great topside job? Makes all our lives much easier, hmmm? Why do I feel like I'm in a loosing battle. Cause I have a great amp that is not quite right,, it's fallen and can't get up. I never had such a great set of tubes waiting for my amp to work. And a new speaker too. And it's been 5-6 years since I've played it, so it means the world to me, to have it working properly.

If only money and logistics was not an issue. Here's hoping Elderly has something close by, or it seems that I am on my own.
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Well
I don't do it from the top, I do it like the factory.
I want it to be all clean and pretty.

But I will do a test 1 resistor from the top, which is the bias adjust.
Because I want to be able tweak it / dial it in.
So maybe I would find the exact resistor from the top,
then install it from the bottom permanently.

But I do like it to be all clean and pretty. That is what you want for re-sale or maintenance
 
Bluesman, how long have you lived where you are? I am pretty sure Elderly will take in your Amp and any tech they use will come get it from there. From all I have learned from folks on here and my other amp building/repairing studies, I would say that once you get it into qualified hands, the amp will be done right and in good working order with minimal discomfort.
 
chilipeppermaniac said:
Bluesman, how long have you lived where you are? I am pretty sure Elderly will take in your Amp and any tech they use will come get it from there. From all I have learned from folks on here and my other amp building/repairing studies, I would say that once you get it into qualified hands, the amp will be done right and in good working order with minimal discomfort.
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Right on. I kinda figure I might be looking at a 50 bench fee, just to be seen. Then add 30 bucks to swap out the parts, so I'm guessing this could cost me nearly a hundred bucks, IDK.

They did not have anything to do with amps about 5-6 years ago, so maybe that changed, and if so, that's great. Without things changing for the better, I'm stuck out of luck. Except for one thing, I didn't find out how far away that service repair tech is. I have a hunch it's within 20-30 miles. I'd have to pay him to come out and get it and return it. I'm taking extra photos of the iron and such, to make sure I know what happens to her.

The plandemic, hehe, oops, the pandemic, has businesses cutting off non-essential personnel, so finding an amp tech is a bit of a hope and a wish, but is certainly within the realm of possibility.
 
Amp Mad Scientist said:
In my own opinion I wouldn't do any modifications.
But get it working right before anything else.

The repair guy will probably pick it up and deliver it.
If it's only 1/2 mile away it won't be difficult.
The Elderly is listed as a certified tube amp service center, and they should have no problem.
Meaning the tech is qualified and uses test equipment.
Click to expand...
Good point and great point about not modding an amp that needs fixed. Well put, and I agree, will do. I am just so glad to hear you point that kind of thing out. My amp does sound fabulous when it's running correctly, so I am only happy to fix it instead of replace it. Lets hope it does not cost an arm and a leg. Any tone cap suggestions in case I am able to take it in? While he's got the lid off, might as well get the other stuff done too. One bench fee instead of two.
 
Would you please expound the low down on that something something that causes the low end resonance. So I can relate that to the amp tech as well. I can't afford to take it in three times for such simple operations. Since a pro is doing the fixes, lets do all that is reasonable to do while lifting the board. I can't afford extra bench fees. It's a do it all at once deal. Ok, or no?
 
I figure should do all three. But would like to hear your thoughts.

1 - Fix the bias, which is not super complicated, but is a crucial professional fix.

Then, after confirming it's fixed, (BTW, what is the proper DC range for EL34's?)
2 - I would ask them to fix that bass resonance bit, thus reversing what my former amp tech did, that I did not like.

And lastly
3 - Add some better quality caps wherever possible and most helpful and affordable. What's the best one's to do first?
 
BluesManRocker said:
Would you please expound the low down on that something something that causes the low end resonance. So I can relate that to the amp tech as well. I can't afford to take it in three times for such simple operations. Since a pro is doing the fixes, lets do all that is reasonable to do while lifting the board. I can't afford extra bench fees. It's a do it all at once deal. Ok, or no?
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Capacitors create resonance in the power supply.
The resonance can be heard as an increase of low frequency, maybe sub-sonic frequency.

Also as the filter capacitor value increases, it draws more current on start-up.

When the cap value is increased the resonance increases too.
That is why (probably) the factory used 10uF instead of 47uF.

I recommend you follow the factory plan, and learn more before you modify anything.

resources.pcb.cadence.com

Capacitor Self-resonant Frequency and Signal Integrity

Real capacitors will start to behave like an RLC network at high frequencies thanks to the capacitor self-resonant frequency.
resources.pcb.cadence.com resources.pcb.cadence.com

"As a real capacitor is actually a series RLC circuit, you can easily determine the capacitor self-resonant frequency using a SPICE model as long as you know the leakage resistance, ESR, and ESL. The capacitance value quoted in the datasheets can be used as C in the RLC network. Leakage resistance is usually large enough to be ignored in circuits that are actively driven, and it can safely be ignored when the capacitor is charged up to a high enough DC voltage. A capacitor self-resonant frequency can range from low MHz values to GHz values. "
 
Amp Mad Scientist said:
Capacitors create resonance in the power supply.
The resonance can be heard as an increase of low frequency, maybe sub-sonic frequency.

Also as the filter capacitor value increases, it draws more current on start-up.

When the cap value is increased the resonance increases too.
That is why (probably) the factory used 10uF instead of 47uF.

I recommend you follow the factory plan, and learn more before you modify anything.

resources.pcb.cadence.com

Capacitor Self-resonant Frequency and Signal Integrity

Real capacitors will start to behave like an RLC network at high frequencies thanks to the capacitor self-resonant frequency.
resources.pcb.cadence.com resources.pcb.cadence.com

"As a real capacitor is actually a series RLC circuit, you can easily determine the capacitor self-resonant frequency using a SPICE model as long as you know the leakage resistance, ESR, and ESL. The capacitance value quoted in the datasheets can be used as C in the RLC network. Leakage resistance is usually large enough to be ignored in circuits that are actively driven, and it can safely be ignored when the capacitor is charged up to a high enough DC voltage. A capacitor self-resonant frequency can range from low MHz values to GHz values. "
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Was that the double ganged dodad on the tone control pot, or something else? The low frequency resonation bit.
 
I'm not trying to re-design the amplifier.
I'm starting where the engineer decided, I'm not assuming that I know more than the factory engineers.
 
Blues............. I put in a Facebook message to a fella who frequents here and other fora for a pretty long time. He also has been a gigging musician from Michigan since the very early 70's I believe. I mentioned you lived near Elderly and sent him the link here to ask him if he has any knowledge of good techs near you. His name is Col Mustard. You may try to PM him here and see what he says too.
 
chilipeppermaniac said:
Blues............. I put in a Facebook message to a fella who frequents here and other fora for a pretty long time. He also has been a gigging musician from Michigan since the very early 70's I believe. I mentioned you lived near Elderly and sent him the link here to ask him if he has any knowledge of good techs near you. His name is Col Mustard. You may try to PM him here and see what he says too.
Click to expand...

Col Mustard he owns a hot dog stand.
It's called "mustard's last stand."
 
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