New Tube Amplifier Problem....

[kuys]

I just purchased a Jetcity JCA22H for use as my hi end on my 12 string rig. I've noticed something strange though, the crunch channel master volume doesn't seem to affect the volume from 1-7 then when it hits 8 the volume jumps dramatically. So it's 0 = off 1-7 loud and then 8 super loud.

Any idea what's going on? JetCity is being cagey, they seem to think it's a preamp tube. Which I've reseated the three out of five I can get to. Two are covered in a the shielding case (?) which I can't seem to get off.

What do you think?

[Tubehed]

I'm not familiar with that particular amp, but it sounds like two of the preamp tubes have tube shields. These are cylindrical shaped and spring loaded. They should be removable by pushing down and twisting. They will pop right up and then you will be able to access the tubes.

[kuys]

Thanks for the help, good sir.

Clockwise? Counter?

[Tubehed]

Try both directions. The shield will only twist one way (clockwise or counter-clockwise, depending on how it is mounted) when you push down on it.

[kuys]

I've switched the tubes around and even with adding two new working groove tubes to the mix. No change.....

Starting to think it's a bad pot.