1 Hipbone 2 months ago Just replaced the el84 tubes in my main amp, a Vox ac10c1The amp started sounding like crap. The power tubes were microphonic.... made some interesting sounds all on their own.Replaced them with a pair of Mulllard el84s. The amp sounds very good now. My question is... should I replace the preamp and inverter tubes at this time? I gig often and crank this little amp up most of the time. How long do pre-amp tubes last in a little 10watt beast?