One of my preamp tubes has gone microphonic... Mark IV Ques.

[Random Hero]

Basically, it squeals when the volume is above 3 on the output, and it appears to only happen on the Lead Channel, although I haven't had time to perform the "pencil tap test" yet.

I didn't know what the hell was going on earlier! I thought it was something in the power or something, this random ringing after I turned the guitar volume down. I ended up turning the amp off, did some reading up on microphonics and it sounds exactly like what's happening.
Turned it back on 15 minutes ago, nothing plugged in, turned the amp up, and it squealed.
So... what should I get to replace the microphonic tube? I don't know much about preamp tubes, so any help would be great.

Another thing - What actually causes preamp tubes to go microphonic all of a sudden? I had the volume up on 4 yesterday, and there was no sign of it. Happened all of a sudden today.



EDIT: So I just did the pencil tap test, and from what I can tell, it's V2. I swapped them around a bit, and the squealing stopped for now.

Also, from what I can see, they're all 12AX7As, so would Electro Harmonix 12AX7EHs be a good choice? Are these "Russians"?

 

[Platypus]

If your MarkIV is a 'B' then they're all 12ax7s.

Tubes just crap out for no reason sometimes... nothing you probably did at all to it. Did you actually replace V2 or just move it around with another tube? I would replace that one if it was causing microphonics.

And not to bash EH tubes, but almost every single EH preamp tube I've ever had has gone microphonic extremely fast/prematurely.

 

[phyrexia]

Boogie sells the high grade 12AX7s that are more resistant to microphonics. They are SPAX7s.

 

[Random Hero]

Yeh, oddly, I swapped it around. Then I swapped it back. And now, no microphonics...

I'm gonna get a full set anyways.

What do you guys recommend then, Boogie 12AX7s? I thought they just rebranded other tubes and sold them for more?

 

[disassembled]

You should probably contact doug at dougstubes.com for some recommendations. He has probably retubed more amps than most poeple on this forum and stocks a variety of tubes. I believe he tests them before shipping them out but I am not positive on that one.


Greg

 

[Russ]

I wouldn't say stick with the Boogie tubes. SPAX7's kind of suck. Granted they have a nice little damper sleeve on them but there are better choices for tone. You can get the same type of selection from Doug or Bob. GT actually has a great selection if you want a screened tube you can buy just about anywhere. They also do further screening and provide high gain sets like Bob or Doug too. I like GT's because you can literally get them anywhere. Sure you pay a little more than a nonscreened tube but it is worth it in the long run. No gambling. I am sure Bob and Doug can give great service but you really can't beat walking into your local guitar shop and being able to have tubes in hand that day. Ordering from Bob or Doug at best is overnight delivery but that costs more. GT does JJ's too so even if I wanted JJ's I would go with GT's unless I wanted something specific then I would order from Bob but I might consider ordering a spec from GT anyway.

 

[Russ]

That GT 12AX7-C would have been nice in the 2205. Sometimes I like it in my 2204. I haven't blueprinted the 2210 but it might be leaving today or tomorrow.

 

[Boogiebabies]

I got a couple of GT 12AX7M's from Doug. They had gain ratings from 110 to 115. I've fallen into the M's in the V1 and V5 and Ruby 12AX7C9's in the other 3 spots.

Regarding the SPAX7, I disagree with Russ. They don't kinda suck, they just plain suck. :lol:

 

[Russ]

I was trying to be nice... :lol: I bet those M's sound great.