Dual Rec: Noise, Microphonic knobs.

[Sparco]

I recently changed all my pre-amp tubes because of some loud white noise I was getting
(old topic http://forum.grailtone.com/viewtopic.php?f=24&t=45597).

For a few weeks, all has been fine, no noise at all. Today I notice every part of the head has become microphonic. Even with all the volumes and master output down, tapping anywhere on the head makes noise coming through the speaker cab. The knobs seems very sensitive to this.

Is is possible I need to replace all the power and recto tubes as well? I did just start using two cabs in the last week and a half. Both cabs 8ohm, coming out of the 4ohm jacks on the back of the duo rec, as the manual suggests. Not sure is this has anything to do with it.

Any help would be great, I need to figure this out before the weekend gigs!!!

-Sparco

 

[clutch71]

Tubes sometimes are bad right out of the box. Not mentioning the type you have or where you got them leaves a lot of guessing on our part. Tubes are not made like they used to. The benefit of buying tubes online from the likes or Eurotubes, the tubestore, tubedepot, or Dougstubes is that they are tested and burnt in.

The burn in process helps eliminate bad tubes, that said even going through that process you could still have one Fail. The good news is most of the online companies have a warranty or will work with you to change out the bad one. Mesa has a similar process for burning and testing their tubes to weed out the bad ones. So when you by a Mesa tube you stand a better chance of getting good tubes.

What I recommend is to power the amp up and use your fingernil, chop stick, or pencil eraser to tap each tube individually. The one that rings out or feeds back is the bad tube. Change it out with a spare.

I'm fortunate in that I have access to a tube testor so I can check all my tubes properly. The method described above is a quick and somewhat effective.

Good luck.

 

[Sparco]

I bought them here http://thetubestore.com their office is 5 min drive from me, luckily.

I replaced all my AX7's with brand new Electro Harmonix Tubes.

Do you think I'll be able to hear a clear difference if I tap on the actual tube itself? Like I said, the whole head is microphonic now. Even when I placed my car keys on top of the head, it caused noise to come through!

Now that I think of it, the noise was only REALLY apparent when I was using Channel 3, at a high gain setting.

 

[clutch71]

In the manual you should be able to see which tube is responsible for that channel. That is most likely your culprit. Willing to bet when you locate the tube for the 3rd channel and you flick it with your finger it will start ringing.

I prefer to mix and match preamp tubes and have not had very good luck with EH tubes. They may suit you just fine.

When you say gain way up...be advised the 11-1 is about the sweet spot when cranked. Anything more and you just start to mud up. Low volumes around the house jamming it's OK to drive the preamp gain a little higher. Be sure to read through the manual for some suggested settings and to understand the reaactive eq....