New Mark V:25 is Really Noisy with gain. Tubes??

[nogalian]

Just received my MKV:25 for Christmas. Been having fun experimenting with it for the past few days! BTW a quick "THANK YOU!!" to all the board members who have contributed their opinions and reviews of this fantastic amp. It was pivotal on me making my purchase. Anyho I have noticed when I dial in some gain on channel one or two, say past 11:00, the amp begiins to feedback really badly. Changed cables, tried four different guitars, with or with out loop, near the amp or away from it still feeds back. I have a full size MKV and no issues like this. I have been using a TA30 for the past year or so and even at near full gain did not have this issue. I plan to pull the chassis next and check the preamp tubes later and see if it's a tube problem.
Anybody else have an issue similar to this?? Keeping gain below 10:30 and there are no problems.
Thanks.

 

[jmontgomery]

My money's on a micro phonic preamp tube.

 

[mesa metal]

i agree,,,, my mark V combo was very noisy then i tube rolled for awhile and now have a great tone.....i have a 1959 rca blackplate inV1 sounds great...
my mini mark should be here sometime this week,,,the first thing im going to do before i turn it on is to make sure all the tubes are seated properly