New JVM410C Day

[Leperclown]

Hi all, greetings from Melbourne Australia

A few years ago I had a JVM410 head plus 4x12 Marshall slant cab (V30's), mated to a Boss GT10 for effects and midi switching. Sounded amazing. The only mod I did was to get external bias adjustment pots and test points fitted. C'mon Marshall fit them as standard! Around 2012, I sold it because it was just too heavy for me.

I always missed my JVM, especially Crunch Green & Red cranked. Marshall Kerrang galore.

Well, I'm back in the fold.

I just bought a mint pre-owned JVM 410C combo - looks absolutely brand new. According to the serial number, I think it was built in August 2020 (2020-08?).

I will run my Boss GT-1000 in 4CM for effects, noise gate/s and midi switching.

It was a bit disappointing when I fired it up. It didn't seem to have the Crunch Green & Red Kerrang I had fondly remembered.

Based on research on this forum, I ordered 4 x El34 Mullards + 5 x 12AX7s Tung Sols (with one balanced for Phase Inverter).

I just finished fitting the tubes. The JVM is a PITA to get apart (refer my earlier comments about external bias points). I think this will definitely be a mod for me in the near future.

Findings:
All tubes (preamp & power) were 'Marshall' brand - not surprising given the amp's youth,
The bias readings were 56 & 74!

I biased the Mullards at 70.5ma a side. I noticed that the bias fluctuated +/- .3 ma - Is this normal?

Re-assembled the amp (refer earlier comments re PITA).

Difference:
I was hoping that, after spending $300 Aussie on tubes and risking death biasing, that I would notice a difference.

Very happy with the outcome! Amp now sounds as I remembered my earlier JVM410. Lots of kerrang!. The clean green with gain about 10 o'clock is beautiful - almost sounds like I have light compression in the signal chain (I didn't, it was my Yamaha SG1820 (SD 59's) straight into the amp).

Not sure if the original tubes were on the way out, or if the weird biasing contributed to the 'very average' tones. Maybe a combination of the two.

Very happy to be back in Marshall land.

This forum is a great source of information.

Cheers!
Paul

 

[fitz]

HNAD!

2020-08?

(That's week 8, so end of February-ish)
No harm in some spare tubes, but I'd suspect the bias was part of the issue unless there was a problem with one of the stock tubes.
Bias fluctuation could be from line voltage fluctuations?
Re-check after a few hours of burn in on the tubes.

 

[GregM]

Hnad! Hope it goes well!
Edit : and cmon the doggies!

 

[scozz]

Congrats man, glad you’re happy!


Welcome to the Marshall Forum.

 

[Sapient]

Congrats! I do recommend, however, that you plan a track installation connecting your band practice site to your home at least.

Oh ...this too ...

 

[jeffb]

Be careful of the Tung Sols in the cathode follower position. They have a (deserved) reputation for quick demise in the CF.

Congrats on your new amp!

 

[Mitchell Pearrow]

Hi all, greetings from Melbourne Australia

A few years ago I had a JVM410 head plus 4x12 Marshall slant cab (V30's), mated to a Boss GT10 for effects and midi switching. Sounded amazing. The only mod I did was to get external bias adjustment pots and test points fitted. C'mon Marshall fit them as standard! Around 2012, I sold it because it was just too heavy for me.

I always missed my JVM, especially Crunch Green & Red cranked. Marshall Kerrang galore.

Well, I'm back in the fold.

I just bought a mint pre-owned JVM 410C combo - looks absolutely brand new. According to the serial number, I think it was built in August 2020 (2020-08?).

I will run my Boss GT-1000 in 4CM for effects, noise gate/s and midi switching.

It was a bit disappointing when I fired it up. It didn't seem to have the Crunch Green & Red Kerrang I had fondly remembered.

Based on research on this forum, I ordered 4 x El34 Mullards + 5 x 12AX7s Tung Sols (with one balanced for Phase Inverter).

I just finished fitting the tubes. The JVM is a PITA to get apart (refer my earlier comments about external bias points). I think this will definitely be a mod for me in the near future.

Findings:
All tubes (preamp & power) were 'Marshall' brand - not surprising given the amp's youth,
The bias readings were 56 & 74!

I biased the Mullards at 70.5ma a side. I noticed that the bias fluctuated +/- .3 ma - Is this normal?

Re-assembled the amp (refer earlier comments re PITA).

Difference:
I was hoping that, after spending $300 Aussie on tubes and risking death biasing, that I would notice a difference.

Very happy with the outcome! Amp now sounds as I remembered my earlier JVM410. Lots of kerrang!. The clean green with gain about 10 o'clock is beautiful - almost sounds like I have light compression in the signal chain (I didn't, it was my Yamaha SG1820 (SD 59's) straight into the amp).

Not sure if the original tubes were on the way out, or if the weird biasing contributed to the 'very average' tones. Maybe a combination of the two.

Very happy to be back in Marshall land.

This forum is a great source of information.

Cheers!
Paul

To the forum
HNAD

 

[LPMarshall hack]

Great amp!

 

[Sir Don]

If your old setup was too heavy how are you going to manage the weight of the combo?

 

[scozz]

Be careful of the Tung Sols in the cathode follower position. They have a (deserved) reputation for quick demise in the CF.

What’s this about Jeff?

I have Tungsol preamp tubes in my amp, (SC20), do I need to be concerned?

 

[Mitchell Pearrow]

What’s this about Jeff?

I have Tungsol preamp tubes in my amp, (SC20), do I need to be concerned?

I think that they just seem to have a short life span there.
Cheers

 

[jeffb]

What’s this about Jeff?

I have Tungsol preamp tubes in my amp, (SC20), do I need to be concerned?

This has been a thing for years since they came out. The New Sensor reissues, not originals. Whether they will cause damage to an amp if they blow in the CF, IDK- I do know Doug's Tubes has a warning on his product page against using them as a CF. I had 1 of them get really weak not long after purchase and I replaced it, and the same thing happened within a month or so (this was before I knew about the issue, or who Doug's Tubes was)

You'll find plenty of chatter online over the years about them.

 

[scozz]

This has been a thing for years since they came out. The New Sensor reissues, not originals. Whether they will cause damage to an amp if they blow in the CF, IDK- I do know Doug's Tubes has a warning on his product page against using them as a CF. I had 1 of them get really weak not long after purchase and I replaced it, and the same thing happened within a month or so (this was before I knew about the issue, or who Doug's Tubes was)

You'll find plenty of chatter online over the years about them.

Thanks Jeff, but I don’t know what CF is? All three preamp positions in my SC20 have Tungsol 12AX7s, is this somehow risky?

I’ll just get a new set of different brand of preamp tubes if I need to, I don’t want to take any risks with this. I know about the PI position, but I’ve never heard of CF.

 

[jeffb]

Thanks Jeff, but I don’t know what CF is? All three preamp positions in my SC20 have Tungsol 12AX7s, is this somehow risky?

I’ll just get a new set of different brand of preamp tubes if I need to, I don’t want to take any risks with this. I know about the PI position, but I’ve never heard of CF.

I've no idea if it's "risky" only that Tung Sols are not very rugged in that position. I would ask an amp/tube tech what potentially happens when the CF tube dies/blows. I noticed issues (amp didn't sound "right") with mine and by tube rolling I figured it out. Once I figured out it was the CF tube, I put it in the V1/V2 spots and it was obviously on it's last legs . I got a replacement for it and same problem - went from new and tested to $hit very quickly. Later upon doing some research I saw I was not the only person who had issues with their longevity. I stopped using them in the CF and never had any other issues with reduced longevity/getting weak (except for normal 100s of hours of play time wear and tear)

I believe that V2 is the CF in a 1987/1959 or 220x circuit, but don't quote me on that. In a DSL it's V3.

The only position I'd bother replacing it is in the CF. Tung Sols are fine in non CF or PI positions.

 

[scozz]

Sorry @jeffb, but I still don’t know what CF means, or what position CF is in my SC20.

I’ve never heard of it, could you help, or anyone?

 

[jeffb]

Sorry @jeffb, but I still don’t know what CF means, or what position CF is in my SC20.

I’ve never heard of it, could you help, or anyone?

Sorry- CF= Cathode Follower

 

[SkyMonkey]

Sorry @jeffb, but I still don’t know what CF means, or what position CF is in my SC20.

I’ve never heard of it, could you help, or anyone?

A quick look around the net suggests the SC20 CF is half of V2.

 

[Jethro Rocker]

I've no idea if it's "risky" only that Tung Sols are not very rugged in that position.
The only position I'd bother replacing it is in the CF. Tung Sols are fine in non CF or PI positions.

I have had 2 TungSols go real fast in PI slot in 2 of my Marshalls. I would steer clear of them in PI myself. No issues in other spots for me.

 

[jeffb]

I have had 2 TungSols go real fast in PI slot in 2 of my Marshalls. I would steer clear of them in PI myself. No issues in other spots for me.

Good to know.

I've used them there with no issues, but not for any great length of time. To be truthful, I don't really care for them much anywhere in a Marshall. I think they sound better in a EL84/Voxy style amps and Fenders.

 

[Jethro Rocker]

Good to know.

I've used them there with no issues, but not for any great length of time. To be truthful, I don't really care for them much anywhere in a Marshall. I think they sound better in a EL84/Voxy style amps and Fenders.

I love old RFTs, Mullards and Raytheons in my Marshalls