ringing noise from silver cylinder next to tube ???

[Rocketman1281734065]

Hi,

 

I have a Valve Junior combo. It makes a ringing noise from the silver cylinder next to the tube. Does anyone know what this is and how to fix it? What is the silver cylinder?

 

Thanks

 

Don

[cGil]

It's just a simple bayonet-mount tube shield with a spring inside. If it's noisy, remove it. I run my amps without 'em all the time. No problems with noise and the tubes run cooler with ventilation. But if you gig a lot, they can help keep the tubes from wiggling loose. Just check it occasionally if you gig without the shield.

 

To remove it, just give it a turn till the notches in the base line up, and it should either just pop off, or grudgingly be wiggled off. They're thin and bend easily, so sometimes they aren't perfectly round.

 

Gil...

[m-theory]

Those shields are used to cut the chances of RF interference with the 12AX7, as well as to the tubes in place, but I've personally never seen an instance where removing one caused interference issues. I prefer to have them on my amps, because it keeps the tubes from getting damaged by an errant cord entanglement accident, but they're not critical.

 

The ringing COULD be a microphonic 12AX7, also, although if you're hearing the noise directly from that shield, it probably is that spring in there oscillating from vibration.

[cGil]

I used to have a big CRT type TV sitting about 15" above the shelf with three of my amps. Very noisy anywhere within 4 feet with my guitar, but the amps were dead quiet with or without the tube shields or even a cab covering them. And I used to read voltages under there before I got my bench cleared off and setup for hard core work. On my bench, however, the ONLY solution is to turn off the fluorescent lights, cuz shield or no shield, whatever amp is up there is gonna buzz if they're on! I don't plug the amp into the bench's power, either; I use a separate 20A drop dedicated to powering my rig. I've learned to live with it and use it as a signal source for diagnostics. But since then, I haven't felt tube shields were all that necessary as an RF deterrent.

 

Gil...