My Z-Plus started making intermittent static noise, even with no guitar plugged in(stand by is off.) I tapped the preamp tubes and the 12AT7 was microphonic. Replaced the tube but I still got the static. So I replaced the V1 and V2 and the static noise went away. The problem now is if I turn the reverb up to 3 o'clock on the dial it starts to feedback. 2 o'clock is fine and I can play all day. I tried 3 different 12 AT7's with the same result. I even swapped the 12AT7 from my Maz 8, which I can turn the reverb up all the way with not feedback.
What can be causing the feedback?
I rarely turn the reverb up past 9 o'clock on the dial. Noon is a lot of reverb for me, so it is not that big of a deal but it bothers me.
Thanks for any help.
Route 66 Z-28 Carmen Ghia MAZ 8 Z-Plus Jetta Z Verb 11 Guitars, 4 cabinets and lots of Pedals(including a Z-Drive)
Rich, why don't you contact Don in the repairs dept. firstname.lastname@example.org he can guide you through some tests of your Z Plus. My feeling is it's not a tube causing the feedback but a faulty reverb tank.