Jvm 410 - Preamp Tube Layout And Mods

smarc78

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Hi guys,

would anyone know what is the exact layout for preamp tubes for JVM410 and JVM410 HJS? As you could notice the board is labeled from V1-V4 which are power tubes.

also in terms of mods. I have JVM from 2007 which suppose to have issues with heat fuse FS3 and FS4 - i have in on pbc and found the Marshall fix for this. but when contacted Marshall they said "not recommending any mods".

Cheers and thanks
m
 

MonstersOfTheMidway

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Hello.
On a stock 410H, the tube layout on the pcb is as follows:
V1: EL34 power tube
V2: EL34 power tube
V3: EL34 power tube
V4: EL34 power tube
V5: ECC83 preamp tube (phase inverter)

V6: ECC 83 preamp tube (gain stage) has a metal cover
V7: ECC 83 preamp tube (gain stage)
V8: ECC 83 preamp tube (cathode follower)
V9: ECC 83 preamp tube (effects loop and reverb mixer)

The two preamp tubes use for gain stages (V6 and V7) are for the most part switched in and out depending on which channel/mode you're using, but one half if V6 is used in every channel and mode of the 410H. The author of the chart below is describing "V1" and "V2" because the he is using a different reference for what is labeled V6 and V7 on the pcb:

JVM 410H_gain stages #2.PNG

PCB preamp tube V8 (cathode follower) is used in all modes of the crunch channel, OD1 channel, and OD2 channel (I think the clean channel is using a different part of the circuit because of pre-gain tone stack).

PCB preamp tube V9 (effects loop and reverb mixer) is using one half for the effects loop, and the other half for the reverb.

PCB preamp tube V5 (phase inverter) is used by the resonance and presence controls.

If look around the internet, you can find a schematic with better details of the circuit.

As for FS3 and FS4 (heater fuses and holders), Marshall produced a service advisory recommending removal of the fuses and holders. In their place, a wire is used to complete the circuit. Newer board will have FS3 and FS4 already removed, so you don't have to go anything.

Why remove FS3 and FS4? I have seen photos and read in other forum posts that severe burning/charring has occurred at the site of FS3 and/or FS4. In most cases, the problem is not the fuses, but the fuse holders (not sure if these are not soldered correctly or if they're incompatible with the pcb, or something else). To remove or not remove-the choice is yours, but to be on the safe side, it might be a good idea to remove FS3 and FS4.

I bought my 410H brand new in 2008. My amp came with FS3 and FS4. I have chosen not to remove FS3 and FS4 because I have never had a single issue with FS3 and FS4. I have also seen other 410H amps with FS3 and FS4 intact with no problems reported by the owners. I've heard reports that only some 410H have problems at FS3 and FS4 while others do not (I guess I got one of the ones with the "good" fuse holders). I feel pretty safe leaving it as is.

Here is a copy of the service advisory for FS3 and FS4:
JVM HEATER FUSE.jpg

Good luck with your amp.
 
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RickyLee

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Hmmm. I have a 2007 JVM 410H and need to check on this heater fuse thingy.

Mine is 2007-24-02XX . . . .
 

smarc78

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Thanks so much, very appreciated. the tubes are marked funny and i am intending to do some preamp cocktail mix.

i bought amp JVM410 just few weeks ago. as mentioned its 2007 - so i guess the fuse holders are good as it survived. no apparent burning on the board ;-) when I wrote this to Marshall on the website - they replied "we do not recommend any changes" i have sent them the same picture (Marshall has released).

please see in the picture if yours is the same connection. Red and Black coming out of V4 and then little connection from the fuses to WP8 and WP5.

JVM.JPG
 

MonstersOfTheMidway

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Thanks so much, very appreciated. the tubes are marked funny and i am intending to do some preamp cocktail mix.

i bought amp JVM410 just few weeks ago. as mentioned its 2007 - so i guess the fuse holders are good as it survived. no apparent burning on the board ;-) when I wrote this to Marshall on the website - they replied "we do not recommend any changes" i have sent them the same picture (Marshall has released).

please see in the picture if yours is the same connection. Red and Black coming out of V4 and then little connection from the fuses to WP8 and WP5.

View attachment 47402
Hello.

QUICK NOTE: the forum member that posted in this thread with the screen name "santiall" is the JVM designer Santiago Alvarez.

@smarc78 : What preamp tubes do you currently have in your amp?

I very much liked the sound of the stock preamp tubes (Shuguang 12AX7). Unfortunately, one by one they went microphonic starting at about six months after I purchased the amp. Fortunately, I was able to get some of those same preamp tubes from a dealer at a great price.

Additionally, I like and use Tung-Sol 12AX7, Electro-Harmonix 12AX7, JJ ECC83, Tube Amp Doctor 7025-S. I tend to use the Tung-Sol when I want a bit of a brighter sound, and the JJ when I want a bit of a darker sound. The Electro-Harmonix and the Shuguang are a pretty good "middle of the road" preamp tube. I used to mix them up, too, but I now like V6 and V7 to be same tube brand for a more consistent sound (I currently run JJ in those positions).

Not sure what is going on with any of those wires connect to FS3 and FS4 in the picture you posted above (maybe ask the previous owner or keep asking around here if anyone has a similar connection).

As stated in the service bulletin I posted above, the recommended service is complete removal of the the fuses and the fuse holders. Then, soldering wires where the fuse holders were connected to the pcb at FS3 and FS4 (I think it recommends soldering two wires into the pcb at the space for FS3, and two wires into the pcb at the space for FS4.

Here's an old photo of FS3 and FS4 of my stock 2007 JVM410H:
100_4128.JPG
As you can see, at any point there are no wires connected to FS3 and FS4; it's all connected through traces on the pcb. I have not done anything to FS3 and FS4 since it came from the factory; it's all completely stock.

Good luck with your amp. Let us know how things go.
 

smarc78

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those fuses have been replaced, probably because the original ones had issues.
You'll be much better removing those black and red wires (that's not original) and follow the official way to remove the fuses

Thanks Santiago. I have sent the same picture to Marshall website and they replied "Do not recommend any mods". I just bought the amp few weeks ago - its 2007 so what to make sure its all correct.

amp has brutal amount of gain (that i like) and i also own 410HJS - different beast - love them both
 

smarc78

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Hello.

QUICK NOTE: the forum member that posted in this thread with the screen name "santiall" is the JVM designer Santiago Alvarez.

@smarc78 : What preamp tubes do you currently have in your amp?

I very much liked the sound of the stock preamp tubes (Shuguang 12AX7). Unfortunately, one by one they went microphonic starting at about six months after I purchased the amp. Fortunately, I was able to get some of those same preamp tubes from a dealer at a great price.

Additionally, I like and use Tung-Sol 12AX7, Electro-Harmonix 12AX7, JJ ECC83, Tube Amp Doctor 7025-S. I tend to use the Tung-Sol when I want a bit of a brighter sound, and the JJ when I want a bit of a darker sound. The Electro-Harmonix and the Shuguang are a pretty good "middle of the road" preamp tube. I used to mix them up, too, but I now like V6 and V7 to be same tube brand for a more consistent sound (I currently run JJ in those positions).

Not sure what is going on with any of those wires connect to FS3 and FS4 in the picture you posted above (maybe ask the previous owner or keep asking around here if anyone has a similar connection).

As stated in the service bulletin I posted above, the recommended service is complete removal of the the fuses and the fuse holders. Then, soldering wires where the fuse holders were connected to the pcb at FS3 and FS4 (I think it recommends soldering two wires into the pcb at the space for FS3, and two wires into the pcb at the space for FS4.

Here's an old photo of FS3 and FS4 of my stock 2007 JVM410H:
View attachment 47404
As you can see, at any point there are no wires connected to FS3 and FS4; it's all connected through traces on the pcb. I have not done anything to FS3 and FS4 since it came from the factory; it's all completely stock.

Good luck with your amp. Let us know how things go.

thanks for this - really clears it. amp has the original Marshall 12ax7 tubes ;-) probably since new. planning to get JJ for 1 and 2 , EHX for 3 and 4, Softek LPS for 5
 

santiall

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Thanks Santiago. I have sent the same picture to Marshall website and they replied "Do not recommend any mods". I just bought the amp few weeks ago - its 2007 so what to make sure its all correct.

amp has brutal amount of gain (that i like) and i also own 410HJS - different beast - love them both

the modification is for reliability reasons, actually those fuses shouldn't have been there from day 1
 

corvairdoug

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My 410h clean channel volume keeps dropping out, I think maybe the other 3 are affected too, but not as drastically. Could V6 be the culprit?
 

RickyLee

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My buddy is going to try the JJ reverse 12DW7 in his 205H. He is looking to reduce the OD channels filth without any mods.
 

South Park

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I think the fuse holder is hooked to circuit board trace. Check with a meter
 

South Park

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I don’t think the pcb trace can take the heater curent.
 

Caspian

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Hi guys,

would anyone know what is the exact layout for preamp tubes for JVM410 and JVM410 HJS? As you could notice the board is labeled from V1-V4 which are power tubes.

also in terms of mods. I have JVM from 2007 which suppose to have issues with heat fuse FS3 and FS4 - i have in on pbc and found the Marshall fix for this. but when contacted Marshall they said "not recommending any mods".

Cheers and thanks
m

I found that the original Marshall schematics, the common naming of tubes, and some commonly referred diagrams on the net, are all referring different ways to the same tubes. (VERY CONFUSING!)

Lets see step by step:
1, For some stupid reason Marshall numbered the tubes in JVM410 in a weird way.
Marshall's V1 to V4 are power amp tubes.
Marshall's V5 is the phase inverter in the power section.
Marshall's V6 is V1 in common terms which refers to the function of tubes, V1 being the first one after the guitar signal input in the preamp section.
Marshall's V7 is V2
Marshall's V8 is V3

Now, you might think, hurray, then I know everything. Not quite! :)
All preamp tubes have two halves! There are two identical amplification hardware in them. They can be used for independent tasks to do, and they are used for different tasks in deed. The halves are labelled as V1A ("A" side of tube V1) or V1B ("B" side of V1). So when someone says on whatever forum something like "V2 is for overdriving" that is not precise! One halve might do one thing, while the other halve is only doing another thing, when switched on! Depends on the design.

Unfortunately the tube referring mess is not yet over!
On the Marshall schematics (Witch is drawn by the factory and not some random internet guy from nowhere) from the signal path view, a tube's B side comes first, and A side after. Yet Mr. Random Internet Guy draws diagrams and comments posts referring on these tubes in a reversed order way. (Calling B as A and A as B.)
Here is a good example of that on a frequently quoted table:

Marshall 410H melyik cső mikor aktív.PNG

Correcting this table:
so called V1A is in fact V1B (labeled on schematics as V6B)
so called V1B is in fact V1A (labeled on schematics as V6A)
so called V2A is in fact V2B (labeled on schematics as V7B)
so called V2B is in fact V2A (labeled on schematics as V7A)

Here is another frequently quoted diagram, wrongly naming tubes:

Marshall 410H signal flow diagramm.jpg

Again, here the half tube labeled as V1A is in fact V1B (V6B on the schematics)
V1B is in fact V1A (V6A on schematics)
V2A and V2B, V3A and V3B are displayed in reversed order too. A is in fact B and vice versa.

The confusion comes from A being before B which makes sense to label the way of the signal in order. Unfortunately on the original, official Marshall schematics the signal hits the B side of tubes first, and then the A sides. So when we are talking about these tubes, we should be using the terminology that the schematics is using.

If you want to figure out which tube's which side does what, then this "block diagram" is a good help (after you sort out the tube naming in to the right order).
I will name them now according to the diagram (wrongly), just to ease up things.
V1A is a buffer, signal runs through it all the time.
V1B and V2A are gain stages, that are switched in and out according to channel and mode switching. V2A has a switchable additional gain stage too.
V2B is another tube being on all the time in every channel and mode.

The preamp's tone is mostly effected by V1 - V3 (V6 - V8 on schematics)
 

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