Went to NAMM today and bought JJ Tesla tubes for MK IV but..

[Mach1andy]

I went to NAMM today and bought 12ax7 JJ Tesla tubes for my 1996 Mark IV. I bought 3 12ax7cz Select tubes and 3 12ax7acz High Gain for the preamp and 2 JJ EL34s. I got home and put the 2 high gain tubes in the V4 and V3 spot and the Select in the others and when I turned it on, I heard nothing.

So I swapped the inverter for the mesa 12ax7 that was in there before and it powered up. It sounded great... for about 2 minutes.

Rhythm I-- sounds great.
Rhythm II- sounds great as well
Lead-- crackling like a mofo. Sounded like mucus in its 'throat'.

So I switch back to Rhythm II and I hear crackling in the background. Same with Rhythm I.

Here are the questions::

Is there any rule about not putting in the high gain JJ Tesla 12ax7acz tubes into the V3 and V4 position?

Any explanation of why my 12ax7cz Select preamp tube didnt work in the inverter position?

Any suggestions for making it right?

****!

On a good note, I saw the new Mesa amps coming out. They're called Express and they're replacing the F series amps. They look cool and their wattage is selectable to run on just one power tube. One of them was a 1X10 selling for $1099!! Considering I bought a used MVIV in great shape for a few hundred more, I can't see why they continue to price their small models so high. Back to my rant. Help!!

 

[Shep]

sounds to me like a faulty tube..preamp tube's do this..track down the duff tube and take it back to bob and he will fix you up..

 

[Mach1andy]

I've swapped out the tubes in the V3 and V4 pos with the old tubes and everything seems to be ok. Is there a rule about not using JJ Tesla 12AX7ACZ (High Gain) preamp tubes in these positions?

 

[stokes]

If it is a MKIVA the V4 is your reverb tube and should be a 12AT7 and could possibly cause a problem,if it is a IVB both V3&4 are 12ax7's so it is likely a bad tube,there is no reason you cant use "high gain" AX7's in these positions.The tube that didnt work in the PI position is likely bad.