Need help with JVM410HJS

Postby **Pat6969** » 12 Dec 2014, 05:57

I posted over at MarshallForum as well but figured here wouldn't hurt either. I have one power tube not working on my head. I live up north and only have access to 2 matched GT EL34MD's. Where should they go(both on one side, both in the middle, both on the outside?) and can I get details on how to bias and to what mV? I've biased my Mesa amps but I'm sure they are different inside. I did a search but didn't find info on the 410HJS.

Thanks!!

Postby **Mats A** » 12 Dec 2014, 10:53

Don't know about the bias but the two inner valves is the 50W and the two on the outsides is the 100W. So you pull either the two inner or the two outer. You should rebias if you're only going to have two valves. Some say it's not recommended on a 100W amp.
Do you like you're HJS? What do you think of the tone?

Postby **Anitoli** » 13 Dec 2014, 16:00

To get an accurate bias figure you need to know the current going through the tubes and the plate voltage at the anode. Am i correct in assuming your amp has the bias adjust pins on the back?

Postby **Pat6969** » 15 Dec 2014, 11:59

Anitoli wrote:To get an accurate bias figure you need to know the current going through the tubes and the plate voltage at the anode. Am i correct in assuming your amp has the bias adjust pins on the back?

No, I'll have to remove it.

Postby **Mats A** » 20 Dec 2014, 07:25

How did it go?

Postby **Marker** » 20 Dec 2014, 09:22

Mine was 445 V.
I set the bias at 38 mA.

Postby **Pat6969** » 26 Dec 2014, 22:07

I ended up waiting and installing 4 new EL34's. Sounds absolutely killer. I love it!!!!! I did get some KT77's today and I'm anxious to try them.