2:90 question...

[PG13]

I have a minor question about the 2:90...
I know the 2:90 has an internal 12AX7 inside the unit which lasts a long time. When this tube is failing, how does it manifest itself so I truly know the tube is the issue and not something else? Any insight would be greatly appreciated.

 

[Triaxstasy]

There´s actually 3 12AX7s/ECC83 in the 2:90...
- 1 Driver tube that works both channels, each with 1 of its Triodes
- 2 Phase Inverter tubes

Hard to say what could be identified as a driver or PI tube failing....would be staring into a crystal ball....
Could be a lot of signs. Crackling on one channel could point towards a PI tube.....

 

[Jackie]

I experienced a very "woofy" and muddy tone. And the Presence control was almost like it wasn't working at all, I had to dime it to get any change at all.

I replaced the power tubes and that helped a little, but the "non-operational" Presence knob and slight muddiness was still there so I swapped the internal 12AX7s and it was all good!

 

[PG13]

Thanks for taking the time to explain! I appreciate it. I also did not know the 2:90 contained "3" 12AX7's.

 

[Jackie]

BTW as far as roles go, the rightmost one (when facing the preamp) or should I say the one closest to the inputs is the input buffer/driver tube, the other two are PIs.