JVM 410h - bad tube or not?

[DaveTheBrave]

Hi guys,

I have a second hand JVM410h and I have a hard time to find out if there is a bad tube or not.
The amp was built in 2009 and I bought it second hand in 2014, the first guy and me both use it at home - so just at lower volumes.
I had some slight volume drops recently while playing, but since I have a pedal board in between guitar and amp, I am not sure yet if the volume drop comes from the pedal board, or if it is from the amp (tubes). But the volume drop is not even the problem - I only had that a few times and of course when I pay close attention, I can not hear a volume drop at the moment (with or without pedal board).
Now I have noticed another strange thing. A week ago I bought a 1985 Fender Telecaster together with a Marshall VS30R amp (also secondhand) and I just love the sound of the Telecaster on the VS30R amp, because of the typical twang. But the strange thing is, when I hook up the Telecaster to my JVM410 head, there is no twang. It sounds more like a Stratocaster on neck pickup than a Telecaster on neck PU.
If I change the PU's from bridge to neck, I can hear that there is more treble, but the twang is not nearly there as when I play the Tele on the VSR30R valvestate amp.
Now to the essence of my question; is it possible that the JVM has no twang because of a bad tube?
I haven't changed a tube since I got the amp in 2014, and as far as I know, the first owner did not change a tube, too.

Since I don't really have other problems with the amp (no cracking, no noise) I am not sure if the amp just sounds this way, or if a tube could be the problem.
Would be great if someone could help me, I am not sure how to proceed. Tube changing is not exactly cheap I heard, so I don't want to have unnecessary repairs done..

 

[fitz288]

Hi guys,

I have a second hand JVM410h and I have a hard time to find out if there is a bad tube or not.
The amp was built in 2009 and I bought it second hand in 2014, the first guy and me both use it at home - so just at lower volumes.
I had some slight volume drops recently while playing, but since I have a pedal board in between guitar and amp, I am not sure yet if the volume drop comes from the pedal board, or if it is from the amp (tubes). But the volume drop is not even the problem - I only had that a few times and of course when I pay close attention, I can not hear a volume drop at the moment (with or without pedal board).
Now I have noticed another strange thing. A week ago I bought a 1985 Fender Telecaster together with a Marshall VS30R amp (also secondhand) and I just love the sound of the Telecaster on the VS30R amp, because of the typical twang. But the strange thing is, when I hook up the Telecaster to my JVM410 head, there is no twang. It sounds more like a Stratocaster on neck pickup than a Telecaster on neck PU.
If I change the PU's from bridge to neck, I can hear that there is more treble, but the twang is not nearly there as when I play the Tele on the VSR30R valvestate amp.
Now to the essence of my question; is it possible that the JVM has no twang because of a bad tube?
I haven't changed a tube since I got the amp in 2014, and as far as I know, the first owner did not change a tube, too.

Since I don't really have other problems with the amp (no cracking, no noise) I am not sure if the amp just sounds this way, or if a tube could be the problem.
Would be great if someone could help me, I am not sure how to proceed. Tube changing is not exactly cheap I heard, so I don't want to have unnecessary repairs done..

to the forum.

I don't have either of those amps, but if you suspect a tube may be causing you issues, you don't necessarily need to change them all.
First thing I'd suggest is verifying that you get the volume drop with no pedals.
Having a spare preamp tube is never a bad idea.
You can try changing a new (or known good) preamp tube for the ones in the amp, one at a time, to isolate a possible bad tube.

Power tubes are a little trickier as changing them would require biasing and should be done in pairs.
If you're not familiar with changing and biasing power tubes, a trip to a tech may be the best bet.
There are potentially deadly (stop your heart like a toaster) voltages inside an amp.
But you can check the power tubes by plugging straight into the loop return and see if you encounter your mysterious volume drop.

Not sure if I can help with your twang problem...
Different guitars with different amps make different tones.
That's why I have piles of both.

 

[MarshallDog]

What Fitz288 said, plus are you sure when you turn a pedal on its not adjusted properly and the volume drops a bit, I've had that happene. Also, I once owned a JVM 410H and it is more modern sounding than other Marshalls so maybe this is why you are missing the twang??