Rectifier problem - Sudden high pitch sound

[Christian Bonde]

Hi

Just plugged in my Dual Rectifier (the old model) the other day. A high pitch sound started appearing as soon as I cranked up the volume or gain nob. The sound is especially there when no fingers on strings/metal body of the guitar.

Guess this is a tube problem, and if so, could anyone tell me the reason for this/technical explanation for this.

Tried tapping the tubes gently at the socket, and one of the 5U4G tubes made a sound as if something’s loose inside, is this normal?
started.

Hope someone can help me, or maybe experienced the same problem.

Christian

 

[TheBlackman]

definately a tube problem, i'm sure someone else will have a more technical explaination, although that can also happen with extreme gain settings too. Try swapping out the tube in question and see what happens.

 

[BMarchant]

a pre amp tube has gone microphonic. Most likely the V1 tube. The one closest to the transformer. You can test it by lightly tapping it with a pen while the amp is on.

 

[Christian Bonde]

Hi everyone... Went to my local tube dealer today and changed alle the original Mesa tubes with 5 JJ preamp tubes and the 6l6's with 4 JJ EL 34.. plays like a dream againg, but somewhat darker. guess it's the JJ preamp tubes.

 

[BMarchant]

Hi Christian Bonde,

Depending on what pre amp tubes you use, you can fine tune the sound of the amp. The EC83s from JJs have a stronger mid range response but with less high end, which is probably what your hearing. The Sovtek 12AX7LPS is a brighter sounding tube. The Chinese 12AX7C is a good rounded sounding tube. The electro harmonic 12AX7EH can add some high end back. One of my favorite tubes in my Lone Star, yet nasty in my Stiletto Deuce. The best pre amp tube for a Deuce is the GT 12AX7-M (Mullard). The V1 position in the amp is the most critical for sound and quietness. V2 and V3 are the gain stages for the channels. These can also change the sound. Try different types in each V position till you find the ones you like. Then WRITE IT DOWN. Trust me.

Good luck,

Bmarchant