too much breakup on clean channel- MarkIIb

[gonzo]

i'm running my mark2b with the master on about 5.....

and even at 4.5 on the VOL1, i'm getting too much breakup on the clean channel.

what's the best way to go, to clean the front end of the amp up....
12au7?

with single coils, it's not as much a problem...
but with humbuckers, there's just too much drive....

 

[Boogiebabies]

The Volume 1 should stay clean to at least 8. It may be a bad, or dirty Volume 1 pot. I worked on one where the gain would jump around, drop out or just hum. Now that you have a problem, it would not be a bad idea to clean all the pots, tube sockets and blow out any dust in the chassis. Dirty sockets can cause and amp to clip, especially in the power section.
Also, you did not mention if you replaced any of the preamp tubes, so it may not hurt to replace them to possibly diagnose an issue.

 

[gonzo]

well, i just had the entire head in for checkup...

new caps, all that...

totally cleaned...
no noise in any of the components....

everything checked to spec.....

all tubes checked, and still in spec.....

 

[gonzo]

so what DOES putting a 12at7 or Au7 in the V1 preamp slot, do to the gain structure of a MKIIb?

wouldn't it allow me to run the output a bit hotter, which is more the sound i'm going for anyway?

 

[Boogiebabies]

Here is a good article about how the 12A?7 tube family relates to each other in terms of gain.

http://home.comcast.net/~machrone/bjr/bjtubes.htm

 

[gonzo]

interesting about the 12au7...
from that description, i don't think that's what i want.

but, i WILL try the 12AY7 in the V1 slot, and see what that gets me...

also, i think i'll have the VOL1 double checked for spec, just in case.

 

[Dutchman]

How hard are you hitting V1?? I've found that level into V1 can make it break up faster. If you're cookin' V1 you could start turning the heat down there.

On my Mark IIB it'll break up earlier with humbuckers and later with single coils, and that can change on how hot the pickups are.

I think a 5751 might be better than a 12ay7, I have used the 5751 in my IIB
V1 without any troubles but I only used it for a short trial and went back to Mullard 12ax7 in V1. I felt the 5751 sucked down the mojo...YMMV.....