JVM410HJS help!

[Pat6969]

So, I just received my head and one of the power tubes is out, it fires up for about 30 seconds and then goes out(tried it in a couple spots). First, will I damage the amp if I use it with one tube not working? Second, I live up north and the closest guitar store only has one matched pair of GTEL34MD's(Mullard) can I swap out 2 Marshall tubes and leave 2 in and run a mix, I will order 2 more to swap in later. Do I have to re-bias?

Thanks,

Pat

 

[ampmadscientist]

So, I just received my head and one of the power tubes is out, it fires up for about 30 seconds and then goes out(tried it in a couple spots). First, will I damage the amp if I use it with one tube not working? Second, I live up north and the closest guitar store only has one matched pair of GTEL34MD's(Mullard) can I swap out 2 Marshall tubes and leave 2 in and run a mix, I will order 2 more to swap in later. Do I have to re-bias?

Thanks,

Pat

All the tubes need to be in. All must be working.
I recommend you order from here:
https://www.tubesandmore.com/products/vacuum_tubes?filters=Type=Power
Unless you want to pay double at a music store...

It's better to just get 4 new tubes.

Rebias: you always need to check the bias whenever you install power tubes.

 

[LiveHardDieFree]

All the tubes need to be in. All must be working.
I recommend you order from here:
https://www.tubesandmore.com/products/vacuum_tubes?filters=Type=Power
Unless you want to pay double at a music store...

It's better to just get 4 new tubes.

Rebias: you always need to check the bias whenever you install power tubes.

He's right, but he's also right here too:

http://www.marshallforum.com/workbench/74024-removing-2-4-power-tubes.html#post1203394

 

[Marker]

It's a too much expensive amp to be fooling around.
Always run your amp with 4 working tubes, properly biased.

You need to order 2 matched tubes at least; on your amp you set the bias of the tubes by pairs (left pair, right pair) so they need to be matched (left side match, right side match), otherwise one of the tubes will run hotter and last less than the other.

After replacing the tubes (in case the new you fit isn't matched with the others) you need to rebias the amp.

For the JVM HJS to bias the amp you need to take it ouf of the headshell and you need to adjust the trim pots with the amp running; there's high voltages running inside the amp, if you touch the wrong spot with a metallic shaft for example you can get in serious trouble so if you don't have experience with this procedure you better pay a technician to do it.

 

[Pat6969]

It's a too much expensive amp to be fooling around.
Always run your amp with 4 working tubes, properly biased.

You need to order 2 matched tubes at least; on your amp you set the bias of the tubes by pairs (left pair, right pair) so they need to be matched (left side match, right side match), otherwise one of the tubes will run hotter and last less than the other.

After replacing the tubes (in case the new you fit isn't matched with the others) you need to rebias the amp.

For the JVM HJS to bias the amp you need to take it ouf of the headshell and you need to adjust the trim pots with the amp running; there's high voltages running inside the amp, if you touch the wrong spot with a metallic shaft for example you can get in serious trouble so if you don't have experience with this procedure you better pay a technician to do it.

I can get a matched pair of Groove Tube EL34MD's. So if I do that both have to go either on the left side or right side? I assume they don't go middle 2, outside 2? I have biased in the past so that's not a huge issue. What do I bias to in mV?

 

[Masteresgt]

So, I just received my head and one of the power tubes is out, it fires up for about 30 seconds and then goes out(tried it in a couple spots). First, will I damage the amp if I use it with one tube not working? Second, I live up north and the closest guitar store only has one matched pair of GTEL34MD's(Mullard) can I swap out 2 Marshall tubes and leave 2 in and run a mix, I will order 2 more to swap in later. Do I have to re-bias?

Thanks,

Pat

It is the amp with fuse problem you planing to buy ?

JVM can't run with only 3 tubes, even with 2 tubes is not recommended. If your only solution is to take out 2 tubes to replace with your GTEL34MD you will still need to rebias amp!

GTEL34MD are Groove Tube which use Mullard tube; they test and match them. Probably cheaper to order a full quad set at www.thetubestore.com. Try Shuguang, quad set for 70$ !

 

[Masteresgt]

I can get a matched pair of Groove Tube EL34MD's. So if I do that both have to go either on the left side or right side? I assume they don't go middle 2, outside 2? I have biased in the past so that's not a huge issue. What do I bias to in mV?

On JVM, left 2x tube control one side lead of OT and right 2x tube control other side. Left side are biased together and right side are biased together. The only concern is that output can be weird as push-pull tubes are different from one side to other side but some people really like this effect ! Better to order a quad set ! Shipping is fast, 3 days !

For bias setting, you must read plate voltage and calculate the current to gety 65, 70 or even 75% dissipation. Or bias to 35mV for safe value.

 

[Pat6969]

Yes outside 2. On JVM, 2 outside tube control one side lead of OT and are biased together. The only concern is that output can be weird as push-pull tubes are different from one side to other side but some people really like this effect ! Better to order a quad set ! Shipping is fast, 3 days !

For bias setting, you must read plate voltage and calculate the current to gety 65, 70 or even 75% dissipation. Or bias to 35mV for safe value.

Are the bias points marked inside? I did my Mesa but can't remember if there was any markings inside.

 

[ampmadscientist]

I can get a matched pair of Groove Tube EL34MD's. So if I do that both have to go either on the left side or right side? I assume they don't go middle 2, outside 2? I have biased in the past so that's not a huge issue. What do I bias to in mV?

YES it's the MIDDLE two, or the outside TWO.
Like this: X00X
or this: 0XX0

BUT this is VERY important: VERY IMPORTANT!!!
when running 2 tubes in a 4 tube output

16 ohm out becomes 32 ohm
8 ohm out becomes 16 ohm (connect 8 ohm out to 16 ohm cab)
4 ohm out becomes 8 ohm (connect 4 ohm out to 8 ohm cab)
OR risk blowing your amp up!

SO, we discourage people from doing this, because players are VERY confused about speaker impedance.
The likelihood of mistakes, based on assumptions - is VERY high.

NEVER assume anything.
NEVER assume that a speaker is what you "think" it is!

If you have not VERIFIED the speaker impedance, DO NOT GUESS.
GUESSING and ASSUMING is what blows your amplifier to CRAP.
NEVER ASSUME ANYTHING!!!
VERIFY 100% EVERY TIME. NO GUESSING ALLOWED.

YOU HAVE been WARNED.

 

[Pat6969]

YES it's the MIDDLE two, or the outside TWO.
Like this: X00X
or this: 0XX0

BUT this is VERY important: VERY IMPORTANT!!!
when running 2 tubes in a 4 tube output

16 ohm out becomes 32 ohm
8 ohm out becomes 16 ohm (connect 8 ohm out to 16 ohm cab)
4 ohm out becomes 8 ohm (connect 4 ohm out to 8 ohm cab)
OR risk blowing your amp up!

SO, we discourage people from doing this, because players are VERY confused about speaker impedance.
The likelihood of mistakes, based on assumptions - is VERY high.

NEVER assume anything.
NEVER assume that a speaker is what you "think" it is!

If you have not VERIFIED the speaker impedance, DO NOT GUESS.
GUESSING and ASSUMING is what blows your amplifier to CRAP.
NEVER ASSUME ANYTHING!!!
VERIFY 100% EVERY TIME. NO GUESSING ALLOWED.

I'll use 2 stock tubes and the 2 new GT tubes.

 

[ampmadscientist]

I'll use 2 stock tubes and the 2 new GT tubes.

Bad idea.
You have NO idea what the current difference is between 2 pairs of tubes.

You are assuming, and guessing that it's going to work OK.

TWO of the tubes "could be" red plating...
while the other two are operating normally.

LIKE I SAID:
Players are always "assuming and guessing."
You have NOT listened to one word I told you!

A guy with 200X your experience - is TRYING to WARN you!!!
AND you have decided to ignore that warning.

THIS is WHY amps blow up.

WADDLE in your own ignorance.
YOU are making repair shops RICH. (thanks)
It's guys like YOU who keep us (repair shops) in business.

 

[Pat6969]

Bad idea.
You have NO idea what the current difference is between 2 pairs of tubes.

You are assuming, and guessing that it's going to work OK.

TWO of the tubes "could be" red plating...
while the other two are operating normally.

LIKE I SAID:
Players are always "assuming and guessing."
You have NOT listened to one word I told you!

A guy with 200X your experience - is TRYING to WARN you!!!
AND you have decided to ignore that warning.

THIS is WHY amps blow up.

WADDLE in your own ignorance.
YOU are making repair shops RICH. (thanks)
It's guys like YOU who keep us (repair shops) in business.

Well, I have you as well as others posting with advice contrary to yours. With that ignorant attitude I'd prefer if you didn't post in my thread anymore.

 

[The Ozzk]

Well, I have you as well as others posting with advice contrary to yours. With that ignorant attitude I'd prefer if you didn't post in my thread anymore.

Brother, he's really helping you. That's a very, very nice amp. Don't jeopardize a $2000 amp for $75 "savings".

Get a matched quad and bias your amp. It's your only play here.

 

[Pat6969]

Brother, he's really helping you. That's a very, very nice amp. Don't jeopardize a $2000 amp for $75 "savings".

Get a matched quad and bias your amp. It's your only play here.

I realize that and I will wait, just saying there's been other advice in this thread besides his. If he is discounting it all then tell me. I don't know who he is or what his credentials are. Also, a couple posts above I said I had a matched pair of GT tubes and his post down from that says,

Yes, XOOX or OXXO. Looked to me like I could add the GT's. Apparantly not.

 

[Masteresgt]

I have edited my previous post for better clarity.

On JVM, tube pairing are different from standard arrangment: XXOO (V1-V2, V3-V4). V1-V2 shared the same bias, and V3-V4 other bias. You remove either XX or OO and replace with your GT tube and rebias. Not recommended setting, but can work temporary. For an amp of 1700$, I will order a matched quad set...

 

[HOT TUBES 70]

Brother, he's really helping you. That's a very, very nice amp. Don't jeopardize a $2000 amp for $75 "savings".

Get a matched quad and bias your amp. It's your only play here.

Solid Advise !!

 

[Pat6969]

I found a shop that has some Rudy EL34bht tubes. One pair has 215, one has 227 and one has 232 on the pack. Will these work? Or do I actually need to buy them in a quad set?

Edit-Forget it, I'll wait until I find a matched quad. I hear Ruby's are questionable.

 

[sullimd]

From Santiago (Santiall):

"You can pull any tube from either side, doesn't matter. You could pull, 1-4, 2-3, 1-3 or 2-4 and the result will be exactly the same."