What issue may have caused my preamp valve to die?

Microbass · #1 10-04-2010, 04:11 AM

Back in May at a gig I found my Trace V4 to be very distorted (farty, not tube awesomeness) before I got anywhere near gig volume.

Of course, this meant a trip to the tech, it was due a service anyway and they replaced a few resistors here and there. We tested it with a P bass with a darkstar that a seriously hot output, but otherwise the amp sounded good to me.

When I tried it through my own set up, I felt the volume wasn't quite there and the farty breakup still there. I called the techs and he felt it maybe a dead preamp valve - this was a suspicion I had, although I bought a full set of JJ's 4 years ago I was somewhat skeptical they would only last this long.

I opened her up and tried the original TE valves (These are about 14 years old so I keep them for spares) in the different positions and I've found that by replacing the two ECC83's that are next to the power valves i got my volume back as well as a clean tone that I can drive again.

I stopped at this point, so I'm not 100% if it is one or two of the preamp valves that have died, but she's sounding good now anyway. Think I've just got unlucky with those valve(s) or something else?

Cheers for insight I can pass onto my tech...

JimmyM · #2 10-04-2010, 04:28 AM

i think you called it. sometimes they go early.

Microbass · #3 10-04-2010, 06:30 AM

OK, further inspection shows it is a dead valve.
thank goodness for keeping spares! recording is next week! although it is tempting to perhaps replace all the preamp valves... hmm...

BassmanPaul · #4 10-04-2010, 09:34 AM

It's not very often that pre-amp tubes go wrong. They don't really do much actual work. They do go sometimes but usually give you plenty of warning. I've had tubes operating in a pre-amp for more than thirty years and they still test well into the green.

Microbass · #5 10-04-2010, 10:01 AM

Yea this was why I was skeptical that it was the preamp valve but it certainly seems to be the case. It's not local to the socket, I've tried the valve in the 4 different sockets and get similiar distortion/lack of volume in each! The replacement valve I'm using is around 16 years old and it sounds great!

When I think about it I haven't had this much clarity for a long time! Amp has been on all afternoon and using line out to record and no issues! boom!

BassmanPaul · #6 10-04-2010, 10:03 AM

I'm glad you got it sorted and you learned a little bit too. Win win situation.