[Problème] Chute de niveau Mesa Express 5:50

Bonjour,

Je suis un heureux possesseur d'un Mesa Express 5:50 depuis 3 ans maintenant.

Je rencontre depuis quelques jours le problème suivant :
Sur le canal Burn : j'ai des chutes de niveau sonore (genre 2 ou 3 fois moins fort) alors que le canal clean est nickel... Pour récupérer le niveau normal sur le canal burn il faut que je le switch en stand by avant de revenir.

Pour info je l'utilise en class A en mode 5 watts.

Dois je suspecter les 12ax7 du préamp ou les 2 6l6 de la partie ampli de puissance?

Je n'ai pas de lampes d'avance donc je voudrais acheter ce qu'il faut...

Merci d'avance.

D'ailleurs si vous connaissez un bon shop en ligne pour des lampes mesa je suis preneur !

Help !

Pourquoi tu veux acheter des tubes mesa ?

SOUND “DROP-OUTS�? / INTERMITTENT SIGNAL

One Possible Cause

Most (but not all) Mesa/Boogie amplifiers have one or two “cathode follower�? tube stages in their preamps. Tube selection is CRITICAL in these stages.

Specifically, in a 12AX7 tube used as a “cathode follower�?, the voltage difference between that present at the cathode, as compared with the heater voltage, can be withstood or tolerated by certain types of tubes, whereas other tubes will fail. The failure of a “cathode follower“ tube will cause sound dropouts or signal loss.

For the past few years, Mesa has been using two types of 12AX7 tubes: ones originating in Russia (Sovtek EH), and ones originating in China. The Russian (Sovtek) tube is NOT reliable as a cathode follower. Of the tubes we are using today (March 200, ONLY THE CHINESE 12AX7 IS RELIABLE AS A CATHODE FOLLOWER.

In conclusion, if you are troubleshooting for signal dropout in a Mesa/Boogie amp, suspect a cathode follower tube, and try replacing it with a Mesa 12AX7 that is marked as “CHINESE�? (silk-screened on the tube itself).

Below is a partial list of Mesa amps and cathode follower tube locations:

GUITAR AMPS BASS AMPS

Lone Star & LS Special: V3
M-Pulse: V2
Stiletto: V3 & V4
Venture: V2
Road King I: V3 & V4
Big Block 750: V4
Road King II: V3 & V5
Titan: V4
Roadster: V3 & V5
M2000: V2
Dual & Triple (2ch or 3ch): V3 & V4
Bass 400+: V2
Tremoverb: V3 & V4

ANOTHER POSSIBLE SCENARIO may occur in the “SPONGY�? (or on some models, “TWEED�?) power setting: the reduced filament voltage may cause very low output from a RUSSIAN preamp tube. Again, the recommended fix is to replace the “sagging�? tube with the CHINESE type of Mesa 12AX7 – which are more immune to this type of failure.

vérifie si c'est russes ou chinois dedans...

Je vais regarder ça... Le son ne se coupe pas par contre c'est juste un baisse du niveau aléatoire qui redevient normal si je met l'ampli en stand by