#1
I had a pre-amp tube go bad (GT-12AX7 Red-12Ax7WC Sovtek), picked up a Tung-Sol(7025/12A7WA Sovtek) at the closest store on the way to jam. Should there be any issues which a mixed brand of pre-amp tubes? I did notice tonight that playing certain notes, sounded like some vibration noise, but not sure. This did not happen on every note, but seemed to be the higher octave ones. Any thoughts?

Gear:
Epiphone Les Paul Standard - Honeyburst
Fender Hot Rod Deluxe (Red Wine Version)
Tube Screamer T9
Boss Chromatic Tuner TU-2
Metal Muff
Small Clone
Fender G-Dec 15w

#2
using mixed preamp tubes is perfectly acceptable, many people do this on purpose to emphasize certain qualities of different tubes in relation to what they do in the amp. Certain tubes are more susceptible to tube rattle though, especially with combo amps. Even a brand new tube can go microphonic too.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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